POLYMERASE CHAIN REACTION  PCR was invented by Kary B. Mullis in 1983. PCR  The PCR is an in-vitro, enzymatic amplification of a desired sequence of DNA using a pair of oligonucleotide primers.  These primers are complementary to one end of the DNA target sequence.  These are extended towards each other by a thermostable DNA polymerase in a reaction cycle of three steps; denaturation, primer annealing and polymerization (extension). Components of PCR A. Template  PCR can amplify as little as one molecule of starting template. Therefore, any source of DNA that provides one or more target molecules can in principle be used as a template for PCR.  This includes DNA prepared from blood, sperm or any other tissue, from older forensic specimens, from ancient biological samples or in the laboratory from bacterial colonies or plaques as well as purified DNA. B. Primers  Oligonucleotides used for priming, should be atleast 16 nts and preferably 20-24 nts in length.  They should have similar G+C contents so that they anneal to their complementary sequences at similar temperatures.  They are designed to anneal on opposite strands of the target sequence so that they will be extended towards each other by addition of nucleotides to their 3’ ends.  If the DNA sequence being amplified is known, then primer design is relatively easy. C. dNTPs  The 4 dNTPs, dATP, dGTP, dCTP and dTTP, used at saturating concentration (200 m M each). D. Enzymes  Thermostable DNA polymerases from a number of thermophilic bacteria are used for PCR.  The most common is Taq polymerase from Thermusaquaticus. It survives the denaturation step of 95º C for 1-2 min, having a half-life of more than 2hr at this temperature.  It carries a 5’-3’ polymerization dependant exonuclease activity, but lack in 3’-5’ exonuclease activity (proof reading).  Hence, it is more prone for introducing errors. There are high-fiedalitythermostable enzymes with 3’-5’ exonuclease activity. e.g., Vent polymerase, pfu polymerase. E. Buffer  The standard buffer for PCR contains 50 mM KCl, 10 mM Tris.Cl and 1.5 mM MgCl2. pH is approximately 7.2. The presence of divalent cations is critical (Mg2+). PCR cycle  PCR involves a repetitive series of temperature cycles. Each reaction cycle comprises of three stages o Denaturation o Primer annealing and o Extension.  In the first cycle, the target DNA is separated into two strands by heating to 95º C- denaturation.  The temperature is reduced to around 55º C to allow the primers to anneal. The actual temperature depends on the primer lengths and sequences- primer annealing.  After annealing, the temperature is increased to 72º C for optimal polymerization which uses up dNTPs in the reaction mix and requires Mg2+ and new strand of DNA is synthesized.  If PCR was 100% efficient, one target molecule would become 2n after ‘n’ cycles. In practice, 20- 40 cycles are commonly used. Types of PCR There are several types of PCR used. The below mentioned are the most commonly used types of PCR.  RT-PCR  Reverse transcriptase polymerase chain reaction (RT-PCR) is used to convert the RNA template into complementary DNA (cDNA) by using the enzyme reverse transcriptase and then the target is amplified into many copies through PCR steps. RT-PCR is applied to diagnose RNA viruses, mRNA expression etc.  Nested PCR  Nested PCR is a conventional PCR with a second round of amplification using a different set of primers. This second set of primers is specific to a sequence found within the DNA of the initial conventional PCR amplicon. The use of a second amplification step with the "nested" primer set results in a reduced background from products amplified during the initial PCR due to the nested primers’ additional specificity to the region. The amount of amplicon produced is increased as a result of the second round of amplification.  Multiplex PCR  Multiplex PCR is the term used when more than one pair of primers is used in a PCR. The goal of multiplex PCR is to amplify several segments of target DNA simultaneously and thereby to conserve template DNA, save time, and minimize expense. It is a PCR strategy that enables the amplification of multiple DNA targets in one run.  Real time PCR  Real-Time PCR, also called quantitative (real-time) PCR or Real-Time Quantitative PCR (RTQ-PCR), is a method of simultaneous DNA quantification and amplification. Applications  Gene cloning.  Generating template for sequencing.  In-vitro mutagenesis.  Analysis of biological materials for forensic applications.  To study the evolutionary history in the field of molecular palaeontology.  Medical applications such as pre-natal diagnosis of diseases and sexing of embryos.  Detection of infectious diseases. Summary into answer for exam

Here is a concise, exam-ready summary of Polymerase Chain Reaction (PCR):

Polymerase Chain Reaction (PCR)

Definition & Discovery

Invented by Kary B. Mullis in 1983
PCR is an in-vitro enzymatic amplification of a specific DNA sequence using a pair of oligonucleotide primers

Components of PCR

Component	Key Details
Template DNA	As little as one molecule is sufficient; sources include blood, sperm, tissue, forensic/ancient specimens, bacterial colonies
Primers	Oligonucleotides; minimum 16 nt, preferably 20-24 nt; similar G+C content; anneal on opposite strands; extended at 3' ends
dNTPs	All 4 types (dATP, dGTP, dCTP, dTTP) at 200 µM each (saturating concentration)
Enzyme	Taq polymerase (from Thermus aquaticus); thermostable; half-life >2 hr at 95°C; has 5'→3' exonuclease but lacks 3'→5' proofreading - prone to errors. High-fidelity alternatives: Vent, Pfu polymerase (have 3'→5' exonuclease)
Buffer	50 mM KCl, 10 mM Tris-Cl, 1.5 mM MgCl₂, pH ~7.2; Mg²⁺ is critical

PCR Cycle (3 Steps per Cycle)

Step 1: DENATURATION     → 95°C  → Separates double-stranded DNA
Step 2: PRIMER ANNEALING → ~55°C → Primers bind to complementary sequences
Step 3: EXTENSION        → 72°C  → Taq polymerase synthesizes new strand using dNTPs

Efficiency: 1 molecule → 2ⁿ copies after n cycles (theoretical)
Practical: 20-40 cycles commonly used

Types of PCR

Type	Key Feature	Application
RT-PCR	RNA → cDNA (via reverse transcriptase) → PCR	Diagnose RNA viruses, mRNA expression
Nested PCR	Two rounds of PCR; second set of primers is internal to first amplicon	Increased specificity, reduced background
Multiplex PCR	Multiple primer pairs in one reaction	Amplifies several DNA targets simultaneously; saves time, template, and cost
Real-Time PCR (RTQ-PCR)	Simultaneous amplification + quantification	Quantitative analysis of DNA/RNA

Applications

Gene cloning
Template generation for DNA sequencing
In-vitro mutagenesis
Forensic analysis of biological materials
Molecular palaeontology - evolutionary history studies
Medical/prenatal diagnosis - genetic diseases, embryo sexing
Detection of infectious diseases

High-Yield Exam Points

Taq polymerase: no proofreading (lacks 3'→5' exonuclease) → error-prone
Vent/Pfu polymerases: have proofreading → high fidelity
Mg²⁺ is an essential cofactor for Taq polymerase
Primers must anneal on opposite strands and extend toward each other
RT-PCR converts RNA → cDNA first, then amplifies
Multiplex PCR uses >1 primer pair in a single reaction
Real-Time PCR = quantitative PCR (RTQ-PCR)

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POLYMERASE CHAIN REACTION (PCR)

A Comprehensive Exam Answer - Essay, Flowchart & Table Format

PART I: ESSAY

Introduction & Historical Background

Polymerase Chain Reaction (PCR) was developed by Kary B. Mullis and colleagues (Saiki et al., 1985; Saiki et al., 1988), a milestone in biotechnology that heralded the beginning of molecular diagnostics. Mullis received the Nobel Prize in Chemistry in 1993 for this invention. PCR is a simple in-vitro chemical reaction that permits the synthesis of essentially limitless quantities of a targeted nucleic acid sequence. It is called "Polymerase" because DNA polymerase is the central enzyme. PCR achieves amplification by the action of a thermostable DNA polymerase that, under the right conditions, can copy a strand of DNA.

Definition: PCR is an in-vitro, enzymatic amplification of a desired DNA sequence using a pair of oligonucleotide primers that are complementary to opposite ends of the target sequence, extended toward each other by a thermostable DNA polymerase through repetitive cycles of denaturation, primer annealing, and polymerization (extension).

Components of PCR

A. Template DNA

The template must be DNA - either genomic DNA (gDNA), complementary DNA (cDNA), or plasmid DNA. PCR can amplify as little as one molecule of starting template. Sources include blood, sperm, tissues, ancient/forensic specimens, bacterial colonies, and purified DNA. The template DNA should ideally be highly pure with an absorbance ratio (A260/A280) of ~1.8. A quantity of 0.1 to 200 µg can be used, with an ideal quantity of 30-50 µg.

B. Primers

Primers are synthetic oligonucleotides, typically 18-30 nucleotides in length (minimum 16 nt, preferably 20-24 nt). Design rules:

Similar G+C content so both primers anneal at similar temperatures
Anneal on opposite strands of the target, oriented so that extension proceeds toward each other (5'→3' direction)
Avoid self-complementarity (hairpin loops) or primer-dimer formation
The annealing temperature (Tm) is typically estimated as: Tm ≈ 4(G+C) + 2(A+T) °C
Used at final concentrations of 0.1-0.5 µM in the reaction

C. dNTPs

All four deoxynucleotide triphosphates - dATP, dGTP, dCTP, and dTTP - used at a saturating concentration of 200 µM each (equimolar mixture). They serve as the building blocks incorporated by DNA polymerase.

D. Thermostable DNA Polymerase

Enzyme	Source Organism	Proofreading (3'→5')	Error Rate	Notes
Taq polymerase	Thermus aquaticus	Absent	Higher	Most common; half-life >2 hr at 95°C; has 5'→3' exonuclease activity
Vent polymerase	Thermococcus litoralis	Present	Lower	High-fidelity; preferred when accuracy is critical
Pfu polymerase	Pyrococcus furiosus	Present	Lowest	Highest fidelity thermostable polymerase

Taq polymerase carries a 5'→3' polymerization-dependent exonuclease activity but lacks 3'→5' exonuclease proofreading activity, making it error-prone (~1 error per 10⁵ bases). Vent and Pfu have proofreading activity, making them preferred for cloning and sequencing.

E. Buffer System

The standard buffer contains: 50 mM KCl, 10 mM Tris-HCl (pH ~7.2-8.4), and 1.5 mM MgCl₂. Mg²⁺ is a critical cofactor - it activates the DNA polymerase and stabilizes the primer-template interaction. Mg²⁺ concentration must be optimized carefully: too little reduces yield; too much can cause mispriming.

F. Thermocycler

The whole procedure is carried out in a programmable thermal cycler that precisely controls (1) the temperature at each step, (2) the dwell time at each temperature, and (3) the total number of cycles.

The PCR Cycle - Step by Step

A PCR cycle consists of three steps at different temperatures. Two-step cycling (combined annealing/extension) is also common in diagnostic assays when annealing temperature is close enough to extension temperature.

PART II: FLOWCHART

╔═══════════════════════════════════════════════════════════════╗
║           POLYMERASE CHAIN REACTION - PROCESS FLOW           ║
╚═══════════════════════════════════════════════════════════════╝

        ┌────────────────────────────────────┐
        │  REACTION SETUP (Pre-PCR)          │
        │  Mix: Template DNA + Forward &     │
        │  Reverse Primers + dNTPs +         │
        │  Taq Polymerase + Mg²⁺ Buffer      │
        │  Load into Thermocycler            │
        └──────────────┬─────────────────────┘
                       │
                       ▼
        ┌────────────────────────────────────┐
        │  INITIAL DENATURATION              │
        │  95°C for 2-5 minutes              │
        │  (Activates hot-start Taq;         │
        │   fully separates template)        │
        └──────────────┬─────────────────────┘
                       │
                       ▼
        ┌══════════════════════════════════════════════╗
        ║          CYCLE BEGINS (Repeat 20-40x)        ║
        ╠══════════════════════════════════════════════╣
        ║                                              ║
        ║  STEP 1: DENATURATION                        ║
        ║  ┌──────────────────────────────────────┐    ║
        ║  │ 94-95°C for 30-60 seconds            │    ║
        ║  │ Heat breaks H-bonds between strands  │    ║
        ║  │ dsDNA ──────────────► 2 x ssDNA      │    ║
        ║  └──────────────┬───────────────────────┘    ║
        ║                 │                            ║
        ║                 ▼                            ║
        ║  STEP 2: PRIMER ANNEALING                    ║
        ║  ┌──────────────────────────────────────┐    ║
        ║  │ 50-65°C for 30-60 seconds            │    ║
        ║  │ Primers bind complementary sequences │    ║
        ║  │ Forward primer → 5'→3' on one strand │    ║
        ║  │ Reverse primer → 5'→3' on other strand│   ║
        ║  │ Both oriented TOWARD each other      │    ║
        ║  └──────────────┬───────────────────────┘    ║
        ║                 │                            ║
        ║                 ▼                            ║
        ║  STEP 3: EXTENSION / POLYMERIZATION          ║
        ║  ┌──────────────────────────────────────┐    ║
        ║  │ 72°C for 30-120 seconds              │    ║
        ║  │ Taq polymerase adds dNTPs to 3' end  │    ║
        ║  │ of primers (5'→3' synthesis)         │    ║
        ║  │ Rate: ~1000 bp/minute                │    ║
        ║  │ New complementary strands formed     │    ║
        ║  └──────────────┬───────────────────────┘    ║
        ║                 │                            ║
        ║         ← ─ ─ ─ ┘  (Repeat cycle)           ║
        ╚══════════════════════════════════════════════╝
                       │
                       │  After n cycles: 2ⁿ copies
                       │  Practical formula: (1+e)ⁿ
                       │  where e = efficiency (0-1)
                       ▼
        ┌────────────────────────────────────┐
        │  FINAL EXTENSION                   │
        │  72°C for 5-10 minutes             │
        │  Ensures all amplicons fully       │
        │  extended and complete             │
        └──────────────┬─────────────────────┘
                       │
                       ▼
        ┌────────────────────────────────────┐
        │  PRODUCT ANALYSIS / DETECTION      │
        │  • Agarose gel electrophoresis +   │
        │    ethidium bromide staining        │
        │  • Capillary electrophoresis       │
        │  • Probe hybridization             │
        │  • Real-time fluorescence          │
        │  • Mass spectrometry               │
        └────────────────────────────────────┘

Amplification Mathematics:

Cycle	Copies (theoretical)	Notes
0	1	Original template
1	2	First doubling
10	~1,000	Thousand-fold
20	~1,000,000	Million-fold
30	~1,000,000,000	Billion-fold
n	2ⁿ	Theoretical maximum

Practical formula: Total amplification = (1 + e)ⁿ, where e = efficiency (0 < e < 1) and n = number of cycles.

PART III: COMPREHENSIVE TABLES

Table 1 - Components of PCR at a Glance

Component	Specification	Function	Critical Notes
Template DNA	Any DNA source; as little as 1 molecule	Provides the sequence to be amplified	A260/A280 ratio ~1.8 for purity
Forward Primer	18-30 nt; 0.1-0.5 µM	Anneals to antisense strand; initiates synthesis	Must not form hairpins or primer-dimers
Reverse Primer	18-30 nt; 0.1-0.5 µM	Anneals to sense strand; initiates synthesis in opposite direction	Similar Tm to forward primer
dATP	200 µM	Adenine building block	Equimolar with all dNTPs
dGTP	200 µM	Guanine building block	Equimolar with all dNTPs
dCTP	200 µM	Cytosine building block	Equimolar with all dNTPs
dTTP	200 µM	Thymine building block	Equimolar with all dNTPs
Taq Polymerase	0.05 units/µL	Catalyzes 5'→3' DNA synthesis	Lacks proofreading; error-prone
KCl	50 mM	Stabilizes polymerase	Part of standard buffer
Tris-HCl	10 mM, pH ~7.2	Maintains pH	Part of standard buffer
MgCl₂	1.5 mM	Activates Taq; cofactor	Concentration is critical; too much → non-specific bands

Table 2 - Temperature Steps in a Standard PCR Cycle

Step	Temperature	Duration	What Happens
Initial denaturation	95°C	2-5 min	Full template strand separation; hot-start activation
Denaturation	94-95°C	30-60 sec	Breaks hydrogen bonds between complementary strands
Primer annealing	50-65°C	30-60 sec	Primers hybridize to their complementary sequences
Extension	72°C	30-120 sec	Taq adds dNTPs at 3' end of primer (~1 kb/min)
Final extension	72°C	5-10 min	Completes any partial strands
Hold	4-15°C	Indefinite	Reaction storage until analysis

Table 3 - Types of PCR

Type	Principle	Key Feature	Applications
Standard (Conventional) PCR	Basic 3-step cycling	Single primer pair; qualitative	Gene detection, cloning, sequencing templates
RT-PCR	RNA → cDNA (by reverse transcriptase), then PCR	Works with RNA template	RNA virus detection, mRNA expression; e.g., SARS-CoV-2, HIV
Nested PCR	Two successive rounds; second primer set is internal to first amplicon	Increased sensitivity + specificity; 15-30 cycles per round	Rare pathogen detection; confirms first-round identity
Hemi-nested PCR	Variant of nested; one primer is shared between rounds	Slightly less specific than fully nested	Diagnostic microbiology
Multiplex PCR	Multiple primer pairs in one reaction	Amplifies several targets simultaneously	Pathogen panels, deletion analysis, STR genotyping
Real-Time PCR (qPCR)	Fluorescent dyes/probes monitor amplification in real time	Simultaneous amplification + quantification; no post-PCR processing	Viral load quantification, gene expression, food pathogen testing
Digital PCR (dPCR)	Sample partitioned into thousands of droplets; each undergoes independent PCR	Absolute quantification without standard curve; counts positive vs negative partitions	Rare mutation detection, copy number variation, viral load, liquid biopsy
Allele-Specific PCR (AS-PCR)	3' end of primer is specific for a mutant allele	Amplifies only mutant/wild-type allele	SNP genotyping, somatic mutation detection
Long-Range PCR	Special polymerase blends (Taq + proofreading enzyme)	Amplifies 5-30 kb fragments	Structural genomic analysis, large deletions
Hot-Start PCR	Taq is inhibited at low temp; activates only at high temp	Reduces non-specific priming and primer-dimers	Improved specificity for difficult targets
COLD-PCR	Selective denaturation enriches minor alleles	Enriches low-frequency mutant alleles	Cancer mutation detection, liquid biopsy

Table 4 - Comparison of DNA Polymerases Used in PCR

Polymerase	Source	5'→3' Synthesis	5'→3' Exonuclease	3'→5' Proofreading	Fidelity	Best Used For
Taq	Thermus aquaticus	Yes	Yes	No	Low	Routine diagnostic PCR
Vent	Thermococcus litoralis	Yes	No	Yes	High	Cloning, sequencing
Pfu	Pyrococcus furiosus	Yes	No	Yes	Highest	High-accuracy cloning
Tth	Thermus thermophilus	Yes	Yes	No	Low	RT-PCR (has RT activity)

Table 5 - PCR Applications (Expanded)

Domain	Application	Example
Diagnostics	Detection of infectious diseases	COVID-19 (SARS-CoV-2), TB (M. tuberculosis), HIV, Hepatitis
Oncology	Somatic mutation detection, minimal residual disease	KRAS, BRAF mutations; BCR-ABL in CML
Forensics	DNA fingerprinting, identity testing	Crime scene blood/hair identification
Genetics	Prenatal diagnosis, carrier screening	Sickle cell disease, cystic fibrosis, Down's syndrome
Reproductive Medicine	Embryo sexing, PGD	Pre-implantation genetic diagnosis (IVF)
Molecular Palaeontology	Ancient DNA analysis	Evolutionary studies of extinct species
Research	Gene cloning, mutagenesis, sequencing template	Site-directed mutagenesis, cDNA library construction
Microbiology	Pathogen identification, antibiotic resistance genes	mecA (MRSA), vanA (VRE)
Blood Banking	Donor screening	NAT testing for HIV, HCV, HBV
Food Safety	Pathogen detection, GMO detection	Salmonella, E. coli O157:H7

Table 6 - Common PCR Problems and Solutions (Troubleshooting)

Problem	Likely Cause	Solution
No amplification	Insufficient template; primer misdesign; Mg²⁺ too low	Check template quality/quantity; re-design primers; optimize Mg²⁺
Non-specific bands	Annealing temp too low; Mg²⁺ too high	Increase annealing temperature; reduce MgCl₂; use hot-start Taq
Primer-dimer	Primer self-complementarity	Redesign primers; use hot-start PCR
Smear on gel	Over-amplification; template degradation	Reduce cycle number; improve template quality
False positives	Carry-over contamination (prior PCR products)	Use dUTP + UNG (uracil-N-glycosylase); closed-tube/real-time methods; UV decontamination

Table 7 - Post-PCR Detection Methods

Method	Principle	Use
Agarose gel electrophoresis + EtBr	Size-based separation; intercalating dye	Classical; confirms product size
Capillary electrophoresis	High-resolution size discrimination	Finer band sizing, fragment analysis
Probe hybridization	Probe binds specifically to product	Confirms identity; used in real-time PCR
Real-time fluorescence (SYBR/TaqMan)	Fluorescent signal during amplification	Quantitative; no post-PCR steps
Mass spectrometry	Precise molecular weight of product	Accurate sizing, multiplexing
DNA sequencing	Sequence determination of amplicon	Gold standard for product verification

Key Textbook-Sourced Points

The PCR development was a "milestone in biotechnology that heralded the beginning of molecular diagnostics" - Henry's Clinical Diagnosis and Management by Laboratory Methods, 23rd Ed.
"After 20 cycles of PCR, a million-fold amplification is achieved, and after 30 cycles, a billion-fold" - Henry's Clinical Diagnosis, p. 1597
Nested PCR's "major disadvantage is the high rate of contamination that can occur during the transfer of first-round products to the second tube" - Henry's Clinical Diagnosis, p. 1597
Digital PCR offers "absolute quantification without the need for standards" and counts positive vs. negative partitions using Poisson statistics - Henry's Clinical Diagnosis, p. 1602
RT-PCR originally used two enzymes (heat-labile AMV-RT + thermostable Taq), but modern single-enzyme systems using thermostable polymerases from Thermus spp. have improved specificity and efficiency - Henry's Clinical Diagnosis, p. 1597

PCR Target Amplification Diagram - Cycles 1 through additional showing exponential amplification of amplicon

Fig: PCR target amplification - showing forward (pink) and reverse (green) primers, and exponential amplification over successive cycles. From Medical Microbiology 9e.

HIGH-YIELD EXAM SUMMARY BOX

┌─────────────────────────────────────────────────────────┐
│              PCR - MUST REMEMBER FACTS                  │
├─────────────────────────────────────────────────────────┤
│ • Inventor: Kary B. Mullis, 1983 (Nobel 1993)           │
│ • Primer length: 18-30 nt (min 16 nt)                  │
│ • dNTPs: 200 µM each (4 types)                          │
│ • Taq: from Thermus aquaticus; NO proofreading          │
│ • Pfu/Vent: HAVE proofreading → high fidelity           │
│ • Mg²⁺ (1.5 mM MgCl₂): CRITICAL cofactor               │
│ • Denaturation: 94-95°C | Annealing: ~55°C              │
│ • Extension: 72°C (optimal for Taq)                     │
│ • Amplification: 2ⁿ (theory); (1+e)ⁿ (practical)       │
│ • 20 cycles = ~10⁶ fold; 30 cycles = ~10⁹ fold         │
│ • RT-PCR: RNA → cDNA first, then amplify                │
│ • Nested: 2 rounds, inner primers → ↑ sensitivity       │
│ • Multiplex: >1 primer pair in same tube                │
│ • qPCR = quantitative = Real-Time PCR                   │
│ • Digital PCR = absolute quantification, no standards  │
└─────────────────────────────────────────────────────────┘

Make it concise form exam writing

POLYMERASE CHAIN REACTION (PCR)

Definition

PCR is an in-vitro enzymatic amplification of a specific DNA sequence using a pair of oligonucleotide primers, extended by a thermostable DNA polymerase through repetitive cycles of denaturation, annealing, and extension.

Invented by Kary B. Mullis, 1983 (Nobel Prize in Chemistry, 1993)

Components

Component	Details
Template DNA	As little as 1 molecule; sources - blood, tissue, forensic/ancient specimens
Primers	18-30 nt long; similar G+C content; anneal on opposite strands; oriented toward each other
dNTPs	dATP, dGTP, dCTP, dTTP - each at 200 µM (saturating)
Taq Polymerase	From Thermus aquaticus; thermostable; has 5'→3' exonuclease; lacks 3'→5' proofreading
Buffer	50 mM KCl + 10 mM Tris-HCl (pH 7.2) + 1.5 mM MgCl₂ (Mg²⁺ is critical)

High-fidelity alternatives to Taq: Vent polymerase, Pfu polymerase - both have 3'→5' proofreading

PCR Cycle - Flowchart

REACTION SETUP
(Template + Primers + dNTPs + Taq + Mg²⁺ Buffer)
            │
            ▼
INITIAL DENATURATION ── 95°C / 2-5 min
(Full strand separation)
            │
            ▼
    ┌───────────────────────────────┐
    │   CYCLE (Repeat 20-40 times) │
    │                               │
    │  STEP 1: DENATURATION         │
    │  94-95°C / 30-60 sec          │
    │  dsDNA → 2 × ssDNA            │
    │           │                   │
    │           ▼                   │
    │  STEP 2: PRIMER ANNEALING     │
    │  50-65°C / 30-60 sec          │
    │  Primers bind complementary   │
    │  sequences on each strand     │
    │           │                   │
    │           ▼                   │
    │  STEP 3: EXTENSION            │
    │  72°C / 30-120 sec            │
    │  Taq adds dNTPs at 3' end     │
    │  New strand synthesized 5'→3' │
    └───────────────────────────────┘
            │
            ▼
FINAL EXTENSION ── 72°C / 5-10 min
(Completes all partial strands)
            │
            ▼
PRODUCT DETECTION
(Gel electrophoresis / qPCR / Sequencing)

Amplification Mathematics

Cycles	Theoretical Copies	Fold Amplification
10	2¹⁰	~1,000×
20	2²⁰	~1,000,000×
30	2³⁰	~1,000,000,000×

Theoretical: 2ⁿ copies after n cycles
Practical: (1 + e)ⁿ where e = efficiency (0 to 1)

Types of PCR

Type	Key Principle	Application
RT-PCR	RNA → cDNA (reverse transcriptase) → PCR	RNA virus detection; mRNA expression
Nested PCR	2 rounds; 2nd primers are internal to 1st amplicon	↑ Sensitivity + specificity; rare pathogens
Multiplex PCR	Multiple primer pairs in one reaction	Simultaneous amplification of several targets
Real-Time (qPCR)	Fluorescence monitors amplification in real time	Quantification of DNA/RNA
Digital PCR (dPCR)	Sample partitioned into droplets; count positive vs negative	Absolute quantification; no standard curve needed
Allele-Specific PCR	3' primer end matches only mutant/wild-type allele	SNP + mutation detection
Hot-Start PCR	Taq inactive at low temp; activates at 95°C	Reduces non-specific bands and primer-dimers

Applications

Gene cloning and in-vitro mutagenesis
Template generation for DNA sequencing
Forensic analysis - DNA fingerprinting
Infectious disease detection - HIV, TB, COVID-19
Prenatal diagnosis - genetic diseases; embryo sexing
Molecular palaeontology - evolutionary studies
Cancer - somatic mutation detection, minimal residual disease
Blood bank NAT screening (HIV, HCV, HBV)

Polymerase Comparison

Polymerase	Organism	Proofreading	Use
Taq	T. aquaticus	✗ No	Routine PCR
Pfu	P. furiosus	✓ Yes	High-fidelity cloning
Vent	T. litoralis	✓ Yes	High-fidelity cloning

Must-Remember Points (High-Yield)

Fact	Value
Inventor	Kary B. Mullis, 1983
Primer length	18-30 nt (min 16 nt)
dNTP concentration	200 µM each
Denaturation temp	94-95°C
Annealing temp	~50-65°C
Extension temp	72°C (optimal for Taq)
Critical cofactor	Mg²⁺ (1.5 mM MgCl₂)
Taq proofreading	Absent (error-prone)
Cycles used	20-40
RT-PCR converts	RNA → cDNA first
Nested PCR advantage	↑ Sensitivity + ↑ Specificity
Digital PCR advantage	Absolute quantification, no standards

Need the above as pdf with images of pcr included as easy drawing

Reading File

Running Command

mkdir -p /tmp/workspace/pcr-pdf && ls /tmp/workspace/pcr-pdf/

Writing File

~/pcr-pdf/make_diagrams.py

"""
Generate PCR diagrams as PNG images for embedding in PDF.
Diagram 1: PCR Cycle Flowchart
Diagram 2: DNA Strand amplification sketch (easy drawing style)
Diagram 3: Types of PCR overview
"""

import matplotlib
matplotlib.use('Agg')
import matplotlib.pyplot as plt
import matplotlib.patches as mpatches
from matplotlib.patches import FancyArrowPatch, FancyBboxPatch, Arc
import matplotlib.patheffects as pe
import numpy as np

# ─────────────────────────────────────────
# DIAGRAM 1: PCR CYCLE FLOWCHART
# ─────────────────────────────────────────
fig1, ax1 = plt.subplots(figsize=(8, 11))
ax1.set_xlim(0, 10)
ax1.set_ylim(0, 14)
ax1.axis('off')
fig1.patch.set_facecolor('#FAFAFA')

def rounded_box(ax, x, y, w, h, label, sublabel='', color='#2196F3', text_color='white', fontsize=11):
    box = FancyBboxPatch((x - w/2, y - h/2), w, h,
                         boxstyle="round,pad=0.15",
                         facecolor=color, edgecolor='white',
                         linewidth=2, zorder=3)
    ax.add_patch(box)
    if sublabel:
        ax.text(x, y + 0.18, label, ha='center', va='center',
                fontsize=fontsize, fontweight='bold', color=text_color, zorder=4)
        ax.text(x, y - 0.25, sublabel, ha='center', va='center',
                fontsize=8.5, color=text_color, zorder=4, style='italic')
    else:
        ax.text(x, y, label, ha='center', va='center',
                fontsize=fontsize, fontweight='bold', color=text_color, zorder=4)

def arrow_down(ax, x, y_top, y_bot, color='#555555'):
    ax.annotate('', xy=(x, y_bot + 0.05), xytext=(x, y_top - 0.05),
                arrowprops=dict(arrowstyle='->', color=color, lw=2))

# Title
ax1.text(5, 13.5, 'PCR CYCLE FLOWCHART', ha='center', va='center',
         fontsize=15, fontweight='bold', color='#1A237E')
ax1.axhline(13.1, color='#1A237E', lw=2, xmin=0.05, xmax=0.95)

# Boxes top to bottom
boxes = [
    (5, 12.4, 7.5, 0.75, 'REACTION SETUP', 'Template + Primers + dNTPs + Taq + Mg²⁺ Buffer', '#37474F'),
    (5, 11.2, 7.5, 0.75, 'INITIAL DENATURATION', '95°C  |  2-5 minutes  |  Complete strand separation', '#B71C1C'),
]
for bx in boxes:
    rounded_box(ax1, *bx)

arrow_down(ax1, 5, 12.05, 11.6)
arrow_down(ax1, 5, 10.85, 10.2)

# Cycle box
cycle_rect = FancyBboxPatch((0.4, 7.3), 9.2, 2.75,
                             boxstyle="round,pad=0.2",
                             facecolor='#E8F5E9', edgecolor='#2E7D32',
                             linewidth=2.5, zorder=2)
ax1.add_patch(cycle_rect)
ax1.text(5, 10.22, '⟳  CYCLE  (Repeat 20–40 times)', ha='center', va='center',
         fontsize=11, fontweight='bold', color='#2E7D32')

# Three steps inside cycle
step_data = [
    (2.4, 9.3, 2.8, 0.85, 'STEP 1\nDENATURATION', '94-95°C\n30-60 sec\ndsDNA → 2×ssDNA', '#C62828'),
    (5.0, 9.3, 2.8, 0.85, 'STEP 2\nANNEALING', '50-65°C\n30-60 sec\nPrimers bind', '#1565C0'),
    (7.6, 9.3, 2.8, 0.85, 'STEP 3\nEXTENSION', '72°C\n30-120 sec\nTaq synthesizes', '#2E7D32'),
]
for sx, sy, sw, sh, sl, ss, sc in step_data:
    box = FancyBboxPatch((sx - sw/2, sy - sh/2), sw, sh,
                         boxstyle="round,pad=0.12",
                         facecolor=sc, edgecolor='white', linewidth=1.5, zorder=4)
    ax1.add_patch(box)
    lines = sl.split('\n')
    ax1.text(sx, sy + 0.22, lines[0], ha='center', va='center',
             fontsize=8.5, fontweight='bold', color='white', zorder=5)
    ax1.text(sx, sy - 0.05, lines[1], ha='center', va='center',
             fontsize=7.5, fontweight='bold', color='white', zorder=5)
    for i, line in enumerate(ss.split('\n')):
        ax1.text(sx, sy - 0.27 - i*0.18, line, ha='center', va='center',
                 fontsize=7, color='#FFECB3', zorder=5)

# Arrows between steps
ax1.annotate('', xy=(3.85, 9.3), xytext=(3.25, 9.3),
             arrowprops=dict(arrowstyle='->', color='#555', lw=1.8))
ax1.annotate('', xy=(6.4, 9.3), xytext=(5.85, 9.3),
             arrowprops=dict(arrowstyle='->', color='#555', lw=1.8))

# Cycle arrow (looping back)
ax1.annotate('', xy=(1.0, 8.6), xytext=(1.0, 7.8),
             arrowprops=dict(arrowstyle='->', color='#2E7D32', lw=2,
                             connectionstyle='arc3,rad=-0.5'))
ax1.text(0.25, 8.2, 'Repeat', ha='center', va='center',
         fontsize=8, color='#2E7D32', fontweight='bold', rotation=90)

arrow_down(ax1, 5, 7.3, 6.75)

# Final extension box
rounded_box(ax1, 5, 6.35, 7.5, 0.75,
            'FINAL EXTENSION', '72°C  |  5-10 minutes  |  Completes all partial strands', '#4527A0')

arrow_down(ax1, 5, 5.98, 5.45)

# Amplification note
ax1.text(5, 5.2, '2ⁿ copies  (theoretical)      (1+e)ⁿ copies  (practical)',
         ha='center', va='center', fontsize=9.5, color='#333',
         bbox=dict(boxstyle='round,pad=0.3', facecolor='#FFF9C4', edgecolor='#F9A825'))

arrow_down(ax1, 5, 4.95, 4.45)

# Detection
rounded_box(ax1, 5, 4.1, 7.5, 0.65,
            'PRODUCT DETECTION', 'Gel Electrophoresis  |  qPCR Fluorescence  |  Sequencing', '#00695C')

# Amplification table
ax1.text(5, 3.45, 'Amplification at key cycles:', ha='center', va='center',
         fontsize=9.5, fontweight='bold', color='#333')

tbl_data = [['Cycles', '10', '20', '30', '40'],
            ['Copies', '~1,000×', '~1,000,000×', '~10⁹×', '~10¹²×']]
col_colors = ['#BBDEFB', '#E3F2FD', '#E3F2FD', '#E3F2FD', '#E3F2FD']
tbl = ax1.table(cellText=tbl_data,
                loc='center',
                bbox=[0.08, 0.14, 0.84, 0.12])
tbl.auto_set_font_size(False)
tbl.set_fontsize(9)
for (r, c), cell in tbl.get_celld().items():
    cell.set_edgecolor('#90CAF9')
    if r == 0:
        cell.set_facecolor('#1565C0')
        cell.set_text_props(color='white', fontweight='bold')
    else:
        cell.set_facecolor('#E3F2FD')

plt.tight_layout()
plt.savefig('/tmp/workspace/pcr-pdf/diagram1_cycle.png', dpi=150, bbox_inches='tight',
            facecolor='#FAFAFA')
plt.close()
print("Diagram 1 saved.")


# ─────────────────────────────────────────
# DIAGRAM 2: DNA STRAND AMPLIFICATION (Easy Drawing)
# ─────────────────────────────────────────
fig2, axes = plt.subplots(1, 3, figsize=(13, 7))
fig2.patch.set_facecolor('#F8F9FA')

colors = {'fwd': '#E91E63', 'rev': '#4CAF50', 'orig': '#1565C0', 'new': '#FF8F00'}

def draw_dna_strand(ax, y, x_start, x_end, color, lw=4, label='', label_x=None, label_y=None):
    ax.plot([x_start, x_end], [y, y], color=color, lw=lw, solid_capstyle='round')
    if label:
        lx = label_x if label_x else (x_start + x_end)/2
        ly = label_y if label_y else y + 0.15
        ax.text(lx, ly, label, ha='center', va='bottom', fontsize=8, color=color, fontweight='bold')

def draw_primer(ax, x_start, x_end, y, color, direction='right'):
    ax.plot([x_start, x_end], [y, y], color=color, lw=6, solid_capstyle='butt',
            alpha=0.9)
    if direction == 'right':
        ax.annotate('', xy=(x_end + 0.05, y), xytext=(x_end - 0.01, y),
                    arrowprops=dict(arrowstyle='->', color=color, lw=2))
    else:
        ax.annotate('', xy=(x_start - 0.05, y), xytext=(x_start + 0.01, y),
                    arrowprops=dict(arrowstyle='->', color=color, lw=2))

def hbonds(ax, x1, x2, y_top, y_bot, n=8, color='#9E9E9E'):
    xs = np.linspace(x1 + 0.1, x2 - 0.1, n)
    for x in xs:
        ax.plot([x, x], [y_top, y_bot], color=color, lw=1, ls='--', alpha=0.6)

for idx, (ax, title, step_color) in enumerate(zip(
        axes,
        ['STEP 1: DENATURATION\n(94-95°C)',
         'STEP 2: ANNEALING\n(50-65°C)',
         'STEP 3: EXTENSION\n(72°C)'],
        ['#C62828', '#1565C0', '#2E7D32'])):

    ax.set_xlim(-0.2, 5.2)
    ax.set_ylim(-0.5, 5.8)
    ax.axis('off')
    ax.set_facecolor('#FFFFFF')

    # Step title
    title_box = FancyBboxPatch((-0.15, 4.9), 5.3, 0.75,
                               boxstyle='round,pad=0.1',
                               facecolor=step_color, edgecolor='none')
    ax.add_patch(title_box)
    lines = title.split('\n')
    ax.text(2.5, 5.45, lines[0], ha='center', va='center',
            fontsize=9.5, fontweight='bold', color='white')
    ax.text(2.5, 5.1, lines[1], ha='center', va='center',
            fontsize=9, color='#FFE082')

    if idx == 0:
        # Double-stranded DNA with H-bonds
        draw_dna_strand(ax, 3.5, 0, 5, colors['orig'], lw=5, label="5'─────────────────3'", label_y=3.75)
        draw_dna_strand(ax, 2.8, 0, 5, colors['orig'], lw=5, label="3'─────────────────5'", label_y=2.55)
        hbonds(ax, 0, 5, 3.5, 2.8, n=10)
        ax.text(2.5, 4.3, 'Double-stranded DNA (dsDNA)', ha='center', fontsize=8.5,
                color='#333', style='italic')
        # Heat arrow
        ax.annotate('', xy=(2.5, 1.9), xytext=(2.5, 2.6),
                    arrowprops=dict(arrowstyle='->', color='#FF5722', lw=2.5))
        ax.text(2.5, 1.65, '🔥  HEAT  →  H-bonds break', ha='center', fontsize=8.5,
                color='#FF5722', fontweight='bold')
        # Two separated strands
        draw_dna_strand(ax, 1.3, 0, 5, colors['orig'], lw=5)
        ax.text(0, 1.5, "5'", fontsize=8, color=colors['orig'], fontweight='bold')
        ax.text(4.85, 1.5, "3'", fontsize=8, color=colors['orig'], fontweight='bold')
        draw_dna_strand(ax, 0.6, 0, 5, colors['orig'], lw=5)
        ax.text(0, 0.78, "3'", fontsize=8, color=colors['orig'], fontweight='bold')
        ax.text(4.85, 0.78, "5'", fontsize=8, color=colors['orig'], fontweight='bold')
        ax.text(2.5, 0.15, '2 × Single-stranded DNA (ssDNA)', ha='center', fontsize=8.5,
                color='#333', style='italic')

    elif idx == 1:
        # Two separated strands + primers annealing
        draw_dna_strand(ax, 3.8, 0, 5, colors['orig'], lw=5)
        ax.text(0, 4.0, "5'", fontsize=8, color=colors['orig'], fontweight='bold')
        ax.text(4.85, 4.0, "3'", fontsize=8, color=colors['orig'], fontweight='bold')
        # Reverse primer on top strand (anneals 3' end)
        draw_primer(ax, 3.2, 4.9, 3.35, colors['rev'], direction='left')
        ax.text(4.05, 3.55, 'Rev primer', fontsize=7.5, color=colors['rev'], fontweight='bold')

        draw_dna_strand(ax, 1.8, 0, 5, colors['orig'], lw=5)
        ax.text(0, 2.0, "3'", fontsize=8, color=colors['orig'], fontweight='bold')
        ax.text(4.85, 2.0, "5'", fontsize=8, color=colors['orig'], fontweight='bold')
        # Forward primer on bottom strand
        draw_primer(ax, 0.1, 1.8, 1.35, colors['fwd'], direction='right')
        ax.text(0.9, 1.5, 'Fwd primer', fontsize=7.5, color=colors['fwd'], fontweight='bold')

        ax.text(2.5, 0.8, "Cool down → Primers bind\ncomplementary sequences",
                ha='center', fontsize=8.5, color='#333', style='italic')
        ax.text(2.5, 0.25, "Primers oriented TOWARD each other →",
                ha='center', fontsize=8, color='#1565C0', fontweight='bold')

    elif idx == 2:
        # Extension: new strands being synthesized
        # Top template
        draw_dna_strand(ax, 4.0, 0, 5, colors['orig'], lw=5)
        ax.text(0, 4.2, "5'", fontsize=8, color=colors['orig'], fontweight='bold')
        ax.text(4.85, 4.2, "3'", fontsize=8, color=colors['orig'], fontweight='bold')
        draw_primer(ax, 3.2, 4.9, 3.55, colors['rev'], direction='left')
        # New strand growing from rev primer
        draw_dna_strand(ax, 3.55, 0.1, 3.15, colors['new'], lw=4)
        ax.text(1.6, 3.7, 'New strand', fontsize=7.5, color=colors['new'], fontweight='bold')
        # Taq symbol
        ax.text(3.0, 3.75, 'Taq→', fontsize=8, color='#FF6F00', fontweight='bold')

        # Bottom template
        draw_dna_strand(ax, 2.0, 0, 5, colors['orig'], lw=5)
        ax.text(0, 2.2, "3'", fontsize=8, color=colors['orig'], fontweight='bold')
        ax.text(4.85, 2.2, "5'", fontsize=8, color=colors['orig'], fontweight='bold')
        draw_primer(ax, 0.1, 1.8, 1.55, colors['fwd'], direction='right')
        draw_dna_strand(ax, 1.55, 1.85, 4.9, colors['new'], lw=4)
        ax.text(3.4, 1.7, 'New strand', fontsize=7.5, color=colors['new'], fontweight='bold')
        ax.text(2.0, 1.75, '←Taq', fontsize=8, color='#FF6F00', fontweight='bold')

        ax.text(2.5, 0.9, "Taq polymerase adds dNTPs\nat 3' end of each primer",
                ha='center', fontsize=8.5, color='#333', style='italic')
        ax.text(2.5, 0.35, "72°C  |  ~1000 bp/minute",
                ha='center', fontsize=9, color='#2E7D32', fontweight='bold')

# Legend
legend_elements = [
    mpatches.Patch(color=colors['orig'], label='Original template strand'),
    mpatches.Patch(color=colors['fwd'], label='Forward primer (pink)'),
    mpatches.Patch(color=colors['rev'], label='Reverse primer (green)'),
    mpatches.Patch(color=colors['new'], label='Newly synthesized strand'),
]
fig2.legend(handles=legend_elements, loc='lower center', ncol=4,
            fontsize=8.5, framealpha=0.9,
            bbox_to_anchor=(0.5, -0.02))

plt.suptitle('PCR DNA STRAND AMPLIFICATION - Three Steps of One Cycle',
             fontsize=13, fontweight='bold', color='#1A237E', y=1.01)
plt.tight_layout(pad=1.0)
plt.savefig('/tmp/workspace/pcr-pdf/diagram2_strands.png', dpi=150, bbox_inches='tight',
            facecolor='#F8F9FA')
plt.close()
print("Diagram 2 saved.")


# ─────────────────────────────────────────
# DIAGRAM 3: TYPES OF PCR
# ─────────────────────────────────────────
fig3, ax3 = plt.subplots(figsize=(12, 7))
ax3.set_xlim(0, 12)
ax3.set_ylim(0, 8)
ax3.axis('off')
fig3.patch.set_facecolor('#F8F9FA')

ax3.text(6, 7.55, 'TYPES OF PCR', ha='center', va='center',
         fontsize=15, fontweight='bold', color='#1A237E')

# Central hub
hub = plt.Circle((6, 4), 0.9, color='#1A237E', zorder=5)
ax3.add_patch(hub)
ax3.text(6, 4.1, 'PCR', ha='center', va='center',
         fontsize=14, fontweight='bold', color='white', zorder=6)
ax3.text(6, 3.7, 'Types', ha='center', va='center',
         fontsize=9, color='#90CAF9', zorder=6)

# Satellite nodes: (angle_deg, label, sublabel, color)
nodes = [
    (90,  'Standard\nPCR',        'Qualitative detection\nSingle primer pair',       '#C62828'),
    (45,  'RT-PCR',               'RNA→cDNA→PCR\nFor RNA viruses, mRNA',              '#AD1457'),
    (0,   'Nested\nPCR',          '2 rounds, inner primers\n↑ Sensitivity + Specificity', '#6A1B9A'),
    (315, 'Multiplex\nPCR',       'Multiple primer pairs\nSeveral targets at once',   '#1565C0'),
    (270, 'Real-Time\nqPCR',      'Fluorescence detection\nQuantitative',             '#00695C'),
    (225, 'Digital\nPCR (dPCR)',  'Droplet partitioning\nAbsolute quantification',   '#E65100'),
    (180, 'Hot-Start\nPCR',       'Taq activated at 95°C\n↓ Non-specific products',  '#37474F'),
    (135, 'Allele-Specific\nPCR', '3\' primer end specific\nSNP & mutation detection','#558B2F'),
]

radius = 2.8
for angle_deg, label, sublabel, color in nodes:
    angle_rad = np.radians(angle_deg)
    cx = 6 + radius * np.cos(angle_rad)
    cy = 4 + radius * np.sin(angle_rad)

    # Spoke
    spoke_x = 6 + 0.95 * np.cos(angle_rad)
    spoke_y = 4 + 0.95 * np.sin(angle_rad)
    end_x = 6 + (radius - 0.7) * np.cos(angle_rad)
    end_y = 4 + (radius - 0.7) * np.sin(angle_rad)
    ax3.plot([spoke_x, end_x], [spoke_y, end_y], color=color, lw=2, alpha=0.7, zorder=3)

    # Node box
    bw, bh = 2.0, 1.0
    box = FancyBboxPatch((cx - bw/2, cy - bh/2), bw, bh,
                         boxstyle='round,pad=0.1',
                         facecolor=color, edgecolor='white', linewidth=1.5, zorder=4)
    ax3.add_patch(box)
    lines = label.split('\n')
    ax3.text(cx, cy + 0.22, lines[0], ha='center', va='center',
             fontsize=9, fontweight='bold', color='white', zorder=5)
    if len(lines) > 1:
        ax3.text(cx, cy - 0.02, lines[1], ha='center', va='center',
                 fontsize=8, color='white', zorder=5)
    for i, sline in enumerate(sublabel.split('\n')):
        ax3.text(cx, cy - 0.3 - i * 0.2, sline, ha='center', va='center',
                 fontsize=7, color='#FFECB3', zorder=5)

plt.tight_layout()
plt.savefig('/tmp/workspace/pcr-pdf/diagram3_types.png', dpi=150, bbox_inches='tight',
            facecolor='#F8F9FA')
plt.close()
print("Diagram 3 saved.")
print("All diagrams done.")

Running Command

cd /tmp/workspace/pcr-pdf && python make_diagrams.py 2>&1

Writing File

~/pcr-pdf/make_pdf.py

"""
Generate full PCR exam notes PDF using ReportLab.
Pages:
  1. Cover + Definition + History
  2. Components table
  3. Diagram 1 - PCR Cycle Flowchart
  4. Diagram 2 - DNA Strand Steps
  5. Types of PCR table
  6. Diagram 3 - Types of PCR radial
  7. Polymerase comparison + Applications
  8. High-yield summary box
"""

from reportlab.lib.pagesizes import A4
from reportlab.lib import colors
from reportlab.lib.units import cm, mm
from reportlab.lib.styles import getSampleStyleSheet, ParagraphStyle
from reportlab.lib.enums import TA_CENTER, TA_LEFT, TA_JUSTIFY
from reportlab.platypus import (
    SimpleDocTemplate, Paragraph, Spacer, Table, TableStyle,
    Image, PageBreak, HRFlowable, KeepTogether
)
from reportlab.platypus.flowables import BalancedColumns
from reportlab.lib.colors import HexColor, white, black
import os

# ── Paths ──────────────────────────────────────────────
OUT = '/tmp/workspace/pcr-pdf/PCR_Exam_Notes.pdf'
D1  = '/tmp/workspace/pcr-pdf/diagram1_cycle.png'
D2  = '/tmp/workspace/pcr-pdf/diagram2_strands.png'
D3  = '/tmp/workspace/pcr-pdf/diagram3_types.png'

# ── Colour palette ──────────────────────────────────────
NAVY   = HexColor('#1A237E')
BLUE   = HexColor('#1565C0')
LBLUE  = HexColor('#E3F2FD')
GREEN  = HexColor('#2E7D32')
LGREEN = HexColor('#E8F5E9')
RED    = HexColor('#B71C1C')
LRED   = HexColor('#FFEBEE')
PURPLE = HexColor('#4527A0')
AMBER  = HexColor('#F57F17')
LAMBER = HexColor('#FFF9C4')
GREY   = HexColor('#37474F')
LGREY  = HexColor('#ECEFF1')
TEAL   = HexColor('#00695C')
LTEAL  = HexColor('#E0F2F1')

# ── Styles ─────────────────────────────────────────────
styles = getSampleStyleSheet()

def S(name, **kw):
    return ParagraphStyle(name, **kw)

title_style = S('Title',
    fontName='Helvetica-Bold', fontSize=22, textColor=white,
    alignment=TA_CENTER, spaceAfter=4)

h1 = S('H1',
    fontName='Helvetica-Bold', fontSize=14, textColor=NAVY,
    spaceBefore=10, spaceAfter=4, borderPad=3)

h2 = S('H2',
    fontName='Helvetica-Bold', fontSize=11, textColor=BLUE,
    spaceBefore=7, spaceAfter=3)

body = S('Body',
    fontName='Helvetica', fontSize=9.5, textColor=GREY,
    leading=14, spaceAfter=3, alignment=TA_JUSTIFY)

bullet = S('Bullet',
    fontName='Helvetica', fontSize=9.5, textColor=GREY,
    leading=13, leftIndent=14, spaceAfter=2,
    bulletFontName='Helvetica', bulletFontSize=9.5)

caption = S('Caption',
    fontName='Helvetica-Oblique', fontSize=8.5, textColor=GREY,
    alignment=TA_CENTER, spaceAfter=4)

highlight = S('Highlight',
    fontName='Helvetica-Bold', fontSize=9.5, textColor=NAVY,
    leading=14, spaceAfter=2)

small = S('Small',
    fontName='Helvetica', fontSize=8.5, textColor=GREY, leading=12)

# ── Helper functions ───────────────────────────────────
def colored_header(text, bg=NAVY, fg=white, size=13):
    """Return a single-cell table that acts as a coloured heading."""
    t = Table([[Paragraph(f'<b>{text}</b>',
                          ParagraphStyle('ch', fontName='Helvetica-Bold',
                                         fontSize=size, textColor=fg,
                                         alignment=TA_LEFT))]],
              colWidths=[17*cm])
    t.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,-1), bg),
        ('TOPPADDING',    (0,0), (-1,-1), 6),
        ('BOTTOMPADDING', (0,0), (-1,-1), 6),
        ('LEFTPADDING',   (0,0), (-1,-1), 10),
        ('ROUNDEDCORNERS', [4,4,4,4]),
    ]))
    return t

def info_box(text, bg=LAMBER, border=AMBER):
    t = Table([[Paragraph(text, ParagraphStyle('ib', fontName='Helvetica-Bold',
                fontSize=9.5, textColor=HexColor('#5D4037'), leading=14))]],
              colWidths=[17*cm])
    t.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,-1), bg),
        ('BOX', (0,0), (-1,-1), 1.5, border),
        ('TOPPADDING',    (0,0), (-1,-1), 7),
        ('BOTTOMPADDING', (0,0), (-1,-1), 7),
        ('LEFTPADDING',   (0,0), (-1,-1), 12),
    ]))
    return t

def plain_table(header_row, data_rows, col_widths,
                header_bg=BLUE, row_bg1=LBLUE, row_bg2=white):
    all_rows = [header_row] + data_rows
    t = Table(all_rows, colWidths=col_widths, repeatRows=1)
    style = [
        ('BACKGROUND', (0,0), (-1,0), header_bg),
        ('TEXTCOLOR',  (0,0), (-1,0), white),
        ('FONTNAME',   (0,0), (-1,0), 'Helvetica-Bold'),
        ('FONTSIZE',   (0,0), (-1,-1), 9),
        ('GRID',       (0,0), (-1,-1), 0.5, HexColor('#B0BEC5')),
        ('ROWBACKGROUNDS', (0,1), (-1,-1), [row_bg1, row_bg2]),
        ('VALIGN',     (0,0), (-1,-1), 'MIDDLE'),
        ('TOPPADDING',    (0,0), (-1,-1), 4),
        ('BOTTOMPADDING', (0,0), (-1,-1), 4),
        ('LEFTPADDING',   (0,0), (-1,-1), 6),
        ('RIGHTPADDING',  (0,0), (-1,-1), 6),
        ('FONTNAME',   (0,1), (-1,-1), 'Helvetica'),
    ]
    t.setStyle(TableStyle(style))
    return t

# ── Page template (header/footer) ──────────────────────
def on_page(canvas, doc):
    canvas.saveState()
    w, h = A4
    # Footer
    canvas.setFillColor(NAVY)
    canvas.rect(0, 0, w, 1.0*cm, fill=1, stroke=0)
    canvas.setFillColor(white)
    canvas.setFont('Helvetica', 8)
    canvas.drawCentredString(w/2, 0.35*cm, f'PCR Exam Notes  •  Page {doc.page}  •  Orris Study Aid')
    # Top accent bar
    canvas.setFillColor(NAVY)
    canvas.rect(0, h - 0.4*cm, w, 0.4*cm, fill=1, stroke=0)
    canvas.restoreState()

# ── Build story ────────────────────────────────────────
story = []

# ════════════════════════════════════════
# COVER BANNER
# ════════════════════════════════════════
cover_data = [[
    Paragraph('POLYMERASE CHAIN REACTION', title_style),
]]
cover_sub  = [[
    Paragraph('Concise Exam Notes  •  With Diagrams  •  Key Tables',
              ParagraphStyle('cs', fontName='Helvetica', fontSize=12,
                             textColor=HexColor('#BBDEFB'), alignment=TA_CENTER)),
]]
cover = Table(cover_data, colWidths=[17*cm])
cover.setStyle(TableStyle([
    ('BACKGROUND', (0,0), (-1,-1), NAVY),
    ('TOPPADDING',    (0,0), (-1,-1), 20),
    ('BOTTOMPADDING', (0,0), (-1,-1), 8),
]))
cover_sub_t = Table(cover_sub, colWidths=[17*cm])
cover_sub_t.setStyle(TableStyle([
    ('BACKGROUND', (0,0), (-1,-1), BLUE),
    ('TOPPADDING',    (0,0), (-1,-1), 8),
    ('BOTTOMPADDING', (0,0), (-1,-1), 12),
]))
story += [cover, cover_sub_t, Spacer(1, 0.4*cm)]

# ════════════════════════════════════════
# SECTION 1 - Definition & History
# ════════════════════════════════════════
story.append(colored_header('1.  DEFINITION & HISTORICAL BACKGROUND'))
story.append(Spacer(1, 0.2*cm))
story.append(Paragraph(
    'PCR is an <b>in-vitro enzymatic amplification</b> of a specific DNA sequence using a pair of '
    'oligonucleotide primers, extended by a <b>thermostable DNA polymerase</b> through repetitive '
    'cycles of denaturation, primer annealing, and extension. It is the most common '
    'nucleic acid amplification (NAA) technique used in clinical and research laboratories.',
    body))
story.append(Spacer(1, 0.2*cm))

hist_data = [
    ['Inventor',   'Kary B. Mullis (with colleagues Saiki et al., 1985; 1988)'],
    ['Year',       '1983 (conceptualized); published 1985'],
    ['Nobel Prize','Chemistry, 1993 (Kary B. Mullis)'],
    ['Significance','Milestone that heralded the beginning of molecular diagnostics'],
]
ht = plain_table(['Detail', 'Information'], hist_data,
                 [4*cm, 13*cm], header_bg=GREY)
story += [ht, Spacer(1, 0.3*cm)]

story.append(info_box(
    'KEY CONCEPT:  "PCR is a simple in-vitro chemical reaction that permits synthesis of essentially '
    'limitless quantities of a targeted nucleic acid sequence."  — Henry\'s Clinical Diagnosis, 23rd Ed.'))
story.append(Spacer(1, 0.35*cm))

# ════════════════════════════════════════
# SECTION 2 - Components
# ════════════════════════════════════════
story.append(colored_header('2.  COMPONENTS OF PCR'))
story.append(Spacer(1, 0.2*cm))

comp_data = [
    ['Template\nDNA',      'Any source', 'As little as 1 molecule\nA260/A280 ratio ~1.8 (purity)',
     'Blood, tissue, forensic specimens,\nancient samples, plasmid, colonies'],
    ['Primers\n(Forward\n& Reverse)', '18-30 nt\n(min 16 nt)', 'Similar G+C content;\nanneal on OPPOSITE strands;\noriented TOWARD each other;\nfinal conc. 0.1-0.5 µM',
     'If sequence unknown, degenerate\nprimers used; avoid hairpins\nand primer-dimers'],
    ['dNTPs\n(4 types)', '200 µM each\n(saturating)', 'dATP, dGTP, dCTP, dTTP\nEquimolar mixture',
     'Building blocks for new strand;\ndepleted with excess cycles'],
    ['Taq\nPolymerase', 'From\nThermus\naquaticus', '5\'→3\' synthesis + 5\'→3\' exonuclease;\nNO 3\'→5\' proofreading;\nhalf-life >2 hr at 95°C',
     'Error-prone (~1/10⁵ bases);\nhot-start variants available;\nalternatives: Vent, Pfu (proofreading)'],
    ['Buffer', 'pH ~7.2-8.4', '50 mM KCl\n10 mM Tris-HCl\n1.5 mM MgCl₂',
     'Mg²⁺ is CRITICAL cofactor;\ntoo low → no product;\ntoo high → non-specific bands'],
]
ct = Table(
    [['Component', 'Amount /\nSource', 'Key Properties', 'Important Notes']] + comp_data,
    colWidths=[2.8*cm, 2.5*cm, 5.5*cm, 6.2*cm], repeatRows=1)
ct.setStyle(TableStyle([
    ('BACKGROUND',    (0,0), (-1,0), BLUE),
    ('TEXTCOLOR',     (0,0), (-1,0), white),
    ('FONTNAME',      (0,0), (-1,0), 'Helvetica-Bold'),
    ('FONTSIZE',      (0,0), (-1,-1), 8.5),
    ('GRID',          (0,0), (-1,-1), 0.5, HexColor('#B0BEC5')),
    ('ROWBACKGROUNDS',(0,1), (-1,-1), [LBLUE, white]),
    ('VALIGN',        (0,0), (-1,-1), 'TOP'),
    ('FONTNAME',      (0,1), (-1,-1), 'Helvetica'),
    ('TOPPADDING',    (0,0), (-1,-1), 5),
    ('BOTTOMPADDING', (0,0), (-1,-1), 5),
    ('LEFTPADDING',   (0,0), (-1,-1), 5),
    # Highlight Mg2+ row
    ('TEXTCOLOR',  (0,4), (-1,4), HexColor('#B71C1C')),
    ('FONTNAME',   (0,4), (-1,4), 'Helvetica-Bold'),
]))
story += [ct, Spacer(1, 0.3*cm)]

# Polymerase comparison
story.append(colored_header('   Polymerase Comparison', bg=GREY, size=11))
story.append(Spacer(1, 0.15*cm))
pol_data = [
    ['Taq',  'Thermus aquaticus',    '✓ Yes',  '✗ No',  'Low',     'Routine diagnostic PCR'],
    ['Pfu',  'Pyrococcus furiosus',  '✓ Yes',  '✓ Yes', 'Highest', 'High-fidelity cloning / sequencing'],
    ['Vent', 'Thermococcus litoralis','✓ Yes', '✓ Yes', 'High',    'High-fidelity cloning'],
    ['Tth',  'Thermus thermophilus', '✓ Yes',  '✗ No',  'Low',     'RT-PCR (has reverse transcriptase activity)'],
]
pt = plain_table(
    ['Enzyme', 'Source Organism', '5\'→3\'\nSynthesis', '3\'→5\'\nProofreading', 'Fidelity', 'Best Used For'],
    pol_data,
    [1.8*cm, 4*cm, 2*cm, 2.2*cm, 2*cm, 5*cm])
story += [pt, Spacer(1, 0.2*cm)]

story.append(PageBreak())

# ════════════════════════════════════════
# SECTION 3 - PCR Cycle Flowchart Diagram
# ════════════════════════════════════════
story.append(colored_header('3.  PCR CYCLE - STEP BY STEP'))
story.append(Spacer(1, 0.2*cm))
story.append(Paragraph(
    'Each cycle consists of <b>three steps</b>: Denaturation → Annealing → Extension. '
    'Two-step cycling (combined annealing/extension) is also used in diagnostic assays '
    'when annealing temperature is close to extension temperature.',
    body))
story.append(Spacer(1, 0.2*cm))

# Temperature table
temp_data = [
    ['Initial Denaturation', '95°C',   '2-5 min',    'Full template strand separation; hot-start activation'],
    ['Denaturation',         '94-95°C','30-60 sec',   'Breaks H-bonds; dsDNA → 2×ssDNA'],
    ['Primer Annealing',     '50-65°C','30-60 sec',   'Primers bind complementary sequences on each strand'],
    ['Extension',            '72°C',   '30-120 sec',  'Taq adds dNTPs at 3\' end of primers (~1 kb/min)'],
    ['Final Extension',      '72°C',   '5-10 min',    'Completes all partial amplicon strands'],
    ['Hold',                 '4-15°C', 'Indefinite',  'Reaction storage; prevents degradation'],
]
tt = plain_table(['Step', 'Temp', 'Duration', 'What Happens'],
                 temp_data, [3.6*cm, 2*cm, 2.4*cm, 9*cm],
                 header_bg=RED)
story += [tt, Spacer(1, 0.3*cm)]

# Diagram 1
story.append(Image(D1, width=14*cm, height=18*cm, hAlign='CENTER'))
story.append(Paragraph('Fig 1: PCR Cycle Flowchart showing all steps, temperatures, and amplification mathematics.',
                        caption))
story.append(PageBreak())

# ════════════════════════════════════════
# SECTION 4 - DNA Strand Diagram
# ════════════════════════════════════════
story.append(colored_header('4.  DNA STRAND AMPLIFICATION - VISUAL GUIDE'))
story.append(Spacer(1, 0.15*cm))
story.append(Image(D2, width=17*cm, height=9.5*cm, hAlign='CENTER'))
story.append(Paragraph(
    'Fig 2: Easy drawing of the three PCR steps at the DNA level. '
    'Pink = forward primer, Green = reverse primer, Blue = original template, Orange = newly synthesized strand.',
    caption))
story.append(Spacer(1, 0.3*cm))

# Amplification maths box
story.append(colored_header('   Amplification Mathematics', bg=GREEN, size=11))
story.append(Spacer(1, 0.15*cm))
amp_data = [
    ['10',  '2¹⁰',  '~1,000×',         'Thousand-fold'],
    ['20',  '2²⁰',  '~1,000,000×',     'Million-fold'],
    ['30',  '2³⁰',  '~1,000,000,000×', 'Billion-fold'],
    ['n',   '2ⁿ',   '(1+e)ⁿ practical', 'e = efficiency (0–1)'],
]
mt = plain_table(['Cycles (n)', 'Theoretical Copies', 'Amplification', 'Notes'],
                 amp_data, [3.5*cm, 4*cm, 5*cm, 4.5*cm],
                 header_bg=GREEN, row_bg1=LGREEN)
story += [mt, Spacer(1, 0.2*cm)]

story.append(info_box(
    'After 20 cycles → ~1,000,000-fold amplification.  After 30 cycles → ~1,000,000,000-fold.  '
    'In practice, total amplification = (1+e)ⁿ where e is efficiency.  '
    'Inhibitors (blood heme, bile salts, urine urea) reduce e and can cause false negatives.'))
story.append(PageBreak())

# ════════════════════════════════════════
# SECTION 5 - Types of PCR
# ════════════════════════════════════════
story.append(colored_header('5.  TYPES OF PCR'))
story.append(Spacer(1, 0.15*cm))
story.append(Image(D3, width=16.5*cm, height=9.5*cm, hAlign='CENTER'))
story.append(Paragraph('Fig 3: Radial overview of major PCR types.', caption))
story.append(Spacer(1, 0.25*cm))

types_data = [
    ['Standard PCR',         'Single primer pair; 3-step cycling',
     'Qualitative; gene detection',  'Routine detection, cloning'],
    ['RT-PCR',               'RNA → cDNA (reverse transcriptase) → PCR',
     'Targets RNA; cDNA intermediate', 'RNA viruses (HIV, COVID-19), mRNA expression'],
    ['Nested PCR',           '2 rounds; 2nd primers internal to 1st amplicon\n(15-30 cycles each round)',
     '↑ Sensitivity + ↑ Specificity;\nrisk: carry-over contamination', 'Rare pathogen detection; confirms 1st-round identity'],
    ['Hemi-Nested PCR',      'One primer shared between both rounds',
     'Slightly less specific than full nested', 'Diagnostic microbiology'],
    ['Multiplex PCR',        'Multiple primer pairs in one reaction',
     'Several targets amplified simultaneously;\nsaves time, template, cost', 'Pathogen panels, STR genotyping, deletion analysis'],
    ['Real-Time qPCR',       'Fluorescence (SYBR/TaqMan probe) monitors\namplification in real time',
     'Simultaneous amplification + quantification;\nno post-PCR gel step', 'Viral load, gene expression, food pathogen quantification'],
    ['Digital PCR (dPCR)',   'Sample partitioned into thousands of droplets;\neach undergoes independent PCR',
     'Absolute quantification WITHOUT standard curve;\ncounts +ve vs -ve droplets (Poisson correction)', 'Rare mutation detection, copy number variation,\nviral load, ctDNA liquid biopsy'],
    ['Allele-Specific PCR',  '3\' end of primer matches ONLY mutant or wild-type allele',
     'Amplifies one allele selectively', 'SNP genotyping, somatic mutation detection'],
    ['Hot-Start PCR',        'Taq inhibited at low temp (Ab or chemical);\nactivates only at 95°C',
     'Reduces non-specific bands and primer-dimers', 'Difficult/GC-rich targets; improved specificity'],
    ['COLD-PCR',             'Selective denaturation enriches minor alleles',
     'Enriches low-frequency mutant alleles', 'Cancer mutation detection, liquid biopsy'],
    ['Long-Range PCR',       'Taq + proofreading enzyme blend',
     'Amplifies 5-30 kb fragments', 'Structural genomic analysis, large deletions'],
]
tyt = Table(
    [['Type', 'Principle', 'Key Feature', 'Applications']] + types_data,
    colWidths=[2.8*cm, 4.5*cm, 4.5*cm, 5.2*cm], repeatRows=1)
tyt.setStyle(TableStyle([
    ('BACKGROUND',    (0,0), (-1,0), PURPLE),
    ('TEXTCOLOR',     (0,0), (-1,0), white),
    ('FONTNAME',      (0,0), (-1,0), 'Helvetica-Bold'),
    ('FONTSIZE',      (0,0), (-1,-1), 8),
    ('GRID',          (0,0), (-1,-1), 0.5, HexColor('#CE93D8')),
    ('ROWBACKGROUNDS',(0,1), (-1,-1), [HexColor('#F3E5F5'), white]),
    ('VALIGN',        (0,0), (-1,-1), 'TOP'),
    ('FONTNAME',      (0,1), (-1,-1), 'Helvetica'),
    ('TOPPADDING',    (0,0), (-1,-1), 4),
    ('BOTTOMPADDING', (0,0), (-1,-1), 4),
    ('LEFTPADDING',   (0,0), (-1,-1), 5),
]))
story += [tyt, PageBreak()]

# ════════════════════════════════════════
# SECTION 6 - Applications
# ════════════════════════════════════════
story.append(colored_header('6.  APPLICATIONS OF PCR'))
story.append(Spacer(1, 0.15*cm))

app_data = [
    ['Infectious Disease\nDiagnosis',   'Detection of bacteria, viruses, fungi, parasites\nin clinical specimens',
     'COVID-19 (SARS-CoV-2), HIV, TB (M. tuberculosis),\nHBV, HCV, HSV, CMV, MRSA, VRE'],
    ['Oncology',                        'Somatic mutation detection; minimal residual disease;\nctDNA in liquid biopsy',
     'KRAS, BRAF, BCR-ABL (CML monitoring), TP53'],
    ['Prenatal Diagnosis',              'Genetic disease screening of fetus;\nembryo sexing in IVF',
     'Sickle cell disease, cystic fibrosis,\npre-implantation genetic diagnosis (PGD)'],
    ['Forensic Science',                'DNA fingerprinting; identity confirmation;\ncrime scene evidence',
     'STR profiling, paternity testing,\ncrime scene blood/hair/saliva identification'],
    ['Blood Banking (NAT)',             'Nucleic acid testing of donor blood\nfor transfusion safety',
     'HIV, HCV, HBV window period detection;\nprevents transfusion-transmitted infections'],
    ['Gene Cloning &\nResearch',        'Amplifying target genes for cloning;\nin-vitro mutagenesis;\nsequencing template',
     'Site-directed mutagenesis, cDNA library\nconstruction, gene expression studies'],
    ['Molecular\nPalaeontology',        'Amplification of ancient DNA from\nextinct organisms',
     'Evolutionary studies, species identification\nfrom museum specimens, fossils'],
    ['Food Safety &\nMicrobiology',     'Pathogen detection in food;\nGMO identification',
     'Salmonella, E. coli O157:H7,\nListeria; GMO labelling compliance'],
    ['Antibiotic\nResistance',          'Detection of resistance genes in\nclinical microbiology',
     'mecA (MRSA), vanA/vanB (VRE),\nKPC (carbapenem resistance)'],
    ['HLA Typing',                      'Tissue matching for organ transplantation',
     'Bone marrow and solid organ\ntransplantation matching'],
]
at = Table(
    [['Domain', 'Description', 'Examples']] + app_data,
    colWidths=[3.5*cm, 6*cm, 7.5*cm], repeatRows=1)
at.setStyle(TableStyle([
    ('BACKGROUND',    (0,0), (-1,0), TEAL),
    ('TEXTCOLOR',     (0,0), (-1,0), white),
    ('FONTNAME',      (0,0), (-1,0), 'Helvetica-Bold'),
    ('FONTSIZE',      (0,0), (-1,-1), 8),
    ('GRID',          (0,0), (-1,-1), 0.5, HexColor('#80CBC4')),
    ('ROWBACKGROUNDS',(0,1), (-1,-1), [LTEAL, white]),
    ('VALIGN',        (0,0), (-1,-1), 'TOP'),
    ('FONTNAME',      (0,1), (-1,-1), 'Helvetica'),
    ('TOPPADDING',    (0,0), (-1,-1), 4),
    ('BOTTOMPADDING', (0,0), (-1,-1), 4),
    ('LEFTPADDING',   (0,0), (-1,-1), 5),
]))
story += [at, Spacer(1, 0.3*cm)]

# ════════════════════════════════════════
# SECTION 7 - Detection Methods
# ════════════════════════════════════════
story.append(colored_header('7.  POST-PCR DETECTION METHODS'))
story.append(Spacer(1, 0.15*cm))
det_data = [
    ['Agarose Gel + EtBr',          'Size-based separation + intercalating dye fluorescence',   'Classical; confirms product size; qualitative'],
    ['Capillary Electrophoresis',   'High-resolution electrophoretic sizing',                    'Fragment analysis; finer band resolution than gel'],
    ['Probe Hybridization',         'Labelled probe binds specifically to amplicon',              'Confirms identity; used in blot-based assays'],
    ['Real-Time Fluorescence',      'SYBR Green (non-specific) or TaqMan probe (specific)',       'Quantitative; no post-PCR gel; closed-tube system'],
    ['Mass Spectrometry',           'Precise molecular weight determination of amplicon',         'Multiplex; accurate sizing; SNP analysis'],
    ['DNA Sequencing',              'Direct sequencing of PCR product',                           'Gold standard; confirms sequence identity'],
    ['Melting Curve Analysis',      'Post-qPCR; monitors fluorescence vs temperature',            'Distinguishes specific product from primer-dimers'],
]
dt = plain_table(['Method', 'Principle', 'Use'], det_data,
                 [4*cm, 6.5*cm, 6.5*cm], header_bg=AMBER)
story += [dt, PageBreak()]

# ════════════════════════════════════════
# SECTION 8 - Troubleshooting
# ════════════════════════════════════════
story.append(colored_header('8.  PCR TROUBLESHOOTING'))
story.append(Spacer(1, 0.15*cm))
tr_data = [
    ['No amplification',       'Insufficient template; Mg²⁺ too low;\nprimers misdesigned; polymerase inactive',
     'Check template quantity/purity; optimize Mg²⁺;\nre-design primers; verify thermocycler program'],
    ['Non-specific bands',     'Annealing temp too low;\nMg²⁺ too high; primer-dimer formation',
     'Raise annealing temp; reduce MgCl₂;\nuse hot-start Taq or touchdown PCR'],
    ['Smear on gel',           'Over-amplification; degraded template;\ntoo many cycles',
     'Reduce cycle number; improve template quality;\ncheck dNTP concentration'],
    ['False positives',        'Carry-over contamination from prior\nPCR products (amplicon contamination)',
     'Use dUTP + UNG (uracil-N-glycosylase);\nclosed-tube real-time PCR; UV decontamination;\nphysical separation of pre/post PCR areas'],
    ['Inhibited reaction',     'Blood heme, bile salts, urine urea,\nheparin, EDTA, SDS',
     'Dilute template; use BSA or betaine;\nswitch to inhibitor-resistant polymerase'],
]
trt = Table(
    [['Problem', 'Likely Cause', 'Solution']] + tr_data,
    colWidths=[3.5*cm, 6cm, 7.5*cm], repeatRows=1)
trt.setStyle(TableStyle([
    ('BACKGROUND',    (0,0), (-1,0), RED),
    ('TEXTCOLOR',     (0,0), (-1,0), white),
    ('FONTNAME',      (0,0), (-1,0), 'Helvetica-Bold'),
    ('FONTSIZE',      (0,0), (-1,-1), 8),
    ('GRID',          (0,0), (-1,-1), 0.5, HexColor('#EF9A9A')),
    ('ROWBACKGROUNDS',(0,1), (-1,-1), [LRED, white]),
    ('VALIGN',        (0,0), (-1,-1), 'TOP'),
    ('FONTNAME',      (0,1), (-1,-1), 'Helvetica'),
    ('TOPPADDING',    (0,0), (-1,-1), 4),
    ('BOTTOMPADDING', (0,0), (-1,-1), 4),
    ('LEFTPADDING',   (0,0), (-1,-1), 5),
]))
story += [trt, Spacer(1, 0.35*cm)]

# ════════════════════════════════════════
# SECTION 9 - HIGH-YIELD SUMMARY BOX
# ════════════════════════════════════════
story.append(colored_header('9.  HIGH-YIELD EXAM SUMMARY', bg=NAVY))
story.append(Spacer(1, 0.2*cm))

hy_data = [
    ['Inventor',                 'Kary B. Mullis, 1983  (Nobel Prize Chemistry 1993)'],
    ['Primer length',            '18-30 nt  (minimum 16 nt)'],
    ['dNTP concentration',       '200 µM each (dATP, dGTP, dCTP, dTTP)'],
    ['Denaturation temp',        '94-95°C'],
    ['Annealing temp',           '~50-65°C  (depends on primer Tm)'],
    ['Extension temp',           '72°C  (optimal for Taq; ~1 kb/min)'],
    ['Critical cofactor',        'Mg²⁺  (1.5 mM MgCl₂)'],
    ['Taq proofreading',         'ABSENT (lacks 3\'→5\' exonuclease) → error-prone'],
    ['Vent / Pfu',               'HAVE proofreading → high fidelity → preferred for cloning'],
    ['Cycles used',              '20-40  (commonly)'],
    ['20 cycles amplification',  '~1,000,000-fold  (10⁶)'],
    ['30 cycles amplification',  '~1,000,000,000-fold  (10⁹)'],
    ['RT-PCR converts',          'RNA → cDNA (by reverse transcriptase) FIRST, then PCR'],
    ['Nested PCR advantage',     '↑ Sensitivity + ↑ Specificity; uses INNER primer set in 2nd round'],
    ['Multiplex PCR',            'Uses >1 primer pair in SAME tube; several targets at once'],
    ['qPCR = ',                  'Quantitative = Real-Time PCR  (simultaneous amplification + detection)'],
    ['Digital PCR advantage',    'Absolute quantification WITHOUT standard curve; droplet partitioning'],
    ['Major inhibitors',         'Blood heme, bile salts, urine urea, heparin, EDTA'],
]
hyt = Table(
    [['Key Point', 'Detail']] + hy_data,
    colWidths=[5.5*cm, 11.5*cm], repeatRows=1)
hyt.setStyle(TableStyle([
    ('BACKGROUND',    (0,0), (-1,0), NAVY),
    ('TEXTCOLOR',     (0,0), (-1,0), white),
    ('FONTNAME',      (0,0), (-1,0), 'Helvetica-Bold'),
    ('FONTSIZE',      (0,0), (-1,-1), 9),
    ('GRID',          (0,0), (-1,-1), 0.5, HexColor('#90CAF9')),
    ('ROWBACKGROUNDS',(0,1), (-1,-1), [LBLUE, white]),
    ('VALIGN',        (0,0), (-1,-1), 'MIDDLE'),
    ('FONTNAME',      (0,1), (0,-1), 'Helvetica-Bold'),
    ('TEXTCOLOR',     (0,1), (0,-1), NAVY),
    ('FONTNAME',      (1,1), (1,-1), 'Helvetica'),
    ('TOPPADDING',    (0,0), (-1,-1), 4),
    ('BOTTOMPADDING', (0,0), (-1,-1), 4),
    ('LEFTPADDING',   (0,0), (-1,-1), 6),
]))
story.append(hyt)

# Footer credit
story.append(Spacer(1, 0.4*cm))
story.append(HRFlowable(width='100%', thickness=1, color=NAVY))
story.append(Paragraph(
    'Sources: Henry\'s Clinical Diagnosis & Management by Laboratory Methods 23e | '
    'Medical Microbiology 9e | Tietz Textbook of Laboratory Medicine 7e | '
    'Saiki et al. 1985 & 1988',
    ParagraphStyle('src', fontName='Helvetica-Oblique', fontSize=7.5,
                   textColor=GREY, alignment=TA_CENTER, spaceBefore=4)))

# ── Build PDF ──────────────────────────────────────────
doc = SimpleDocTemplate(
    OUT,
    pagesize=A4,
    topMargin=1.2*cm,
    bottomMargin=1.5*cm,
    leftMargin=2*cm,
    rightMargin=2*cm,
    title='PCR Exam Notes',
    author='Orris Study Aid',
    subject='Polymerase Chain Reaction - Concise Exam Notes'
)
doc.build(story, onFirstPage=on_page, onLaterPages=on_page)
print(f"PDF saved to: {OUT}")

Running Command

cd /tmp/workspace/pcr-pdf && python make_pdf.py 2>&1

Editing File

~/pcr-pdf/make_pdf.py

Successfully replaced 1 instance(s) of the string in '/tmp/workspace/pcr-pdf/make_pdf.py'

Running Command

cd /tmp/workspace/pcr-pdf && python make_pdf.py 2>&1

Running Command

ls -lh /tmp/workspace/pcr-pdf/

Your PDF is ready! Here's your download link:

PCR Exam Notes

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Section	Content
Cover	Title banner with subtitle
1. Definition & History	Concise definition, history table, key concept quote from textbook
2. Components	Full components table (Template, Primers, dNTPs, Taq, Buffer) + polymerase comparison table (Taq vs Pfu vs Vent vs Tth)
3. PCR Cycle	Temperature/duration table + Fig 1: Full cycle flowchart diagram with all steps, temps, and amplification maths
4. DNA Strand Guide	Fig 2: Easy step-by-step drawing of DNA denaturation, primer annealing, and extension at molecular level (colour-coded strands and primers)
5. Types of PCR	Fig 3: Radial diagram of all 8 types + detailed comparison table (11 types total)
6. Applications	10-domain applications table with examples
7. Detection Methods	Post-PCR detection table (gel, qPCR, sequencing, mass spec etc.)
8. Troubleshooting	Common PCR problems, causes, and solutions
9. High-Yield Summary	18-row must-remember facts table - exam ready

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