Give me answers of the following biochemistry questions

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Biochemistry Questions — Theory & Viva Answers

LONG ANSWER QUESTIONS

Q1. Explain the principle, working, calibration and applications of a pH meter

What is pH? pH = −log[H⁺]. A neutral solution has pH 7; acidic < 7; alkaline > 7.

Principle A pH meter measures the difference in electrical potential (voltage) between a glass electrode (pH-sensitive) and a reference electrode. The glass membrane of the pH electrode is permeable to H⁺ ions; the selective diffusion of H⁺ across it creates a potential difference proportional to the H⁺ concentration of the solution. This voltage is amplified and displayed as a pH value.

Components

Glass electrode — a thin glass bulb filled with a buffered internal solution (usually 0.1 M HCl). The glass membrane selectively responds to H⁺ activity.
Reference electrode — typically a calomel (Hg/Hg₂Cl₂) or silver/silver chloride (Ag/AgCl) electrode that provides a stable, constant reference potential.
Voltmeter / amplifier — measures the potential difference and converts it to pH units.
Temperature compensator — adjusts for the effect of temperature on electrode response (Nernst equation: 59.16 mV per pH unit at 25°C).

Working When the glass electrode is immersed in a test solution, H⁺ ions exchange with ions in the glass membrane surface. This creates a potential (E) described by the Nernst equation:

E = E₀ − 0.0592 × pH (at 25°C)

The voltmeter measures E and the instrument displays the corresponding pH.

Calibration The meter is calibrated using standard buffer solutions of known pH (e.g., pH 4.0, 7.0, 9.2). The two-point calibration corrects for:

Offset (zero-point) — using pH 7.0 buffer
Slope — using a second buffer (e.g., pH 4.0 or 9.2)

The instrument is then ready to measure unknown samples.

Applications

Blood gas analysis (arterial blood pH, acid–base disorders)
Urine pH measurement (renal disease, calculi)
Monitoring fermentation and culture media
Quality control in food, beverages, and pharmaceuticals
Enzyme activity studies (optimal pH determination)
Measurement of gastric acid, CSF, and other body fluids

Q2. Define chromatography. Describe the principle, types, and applications in biochemical analysis

Definition Chromatography is a separation technique in which components of a mixture are distributed between a stationary phase (solid or liquid) and a mobile phase (liquid or gas) that moves through or over the stationary phase. Components separate based on differences in their affinity for the two phases.

Principle Separation depends on the differential migration of solutes. A component with greater affinity for the stationary phase moves slowly; one with greater affinity for the mobile phase moves faster. The ratio of distance traveled by a solute to that traveled by the solvent front is the Rf (retention factor).

Types

Type	Stationary Phase	Mobile Phase	Basis of Separation
Paper chromatography	Cellulose paper (water)	Organic solvent	Partition
Thin layer chromatography (TLC)	Silica gel/alumina on plate	Organic solvent	Adsorption
Column chromatography	Solid packed in column	Liquid	Adsorption/partition
Ion-exchange chromatography	Charged resin	Buffer	Ionic charge
Gel filtration (size-exclusion)	Porous beads	Buffer	Molecular size
Affinity chromatography	Ligand-bound matrix	Buffer	Biological affinity
Gas chromatography (GC)	Liquid/solid	Inert gas	Volatility/partition
HPLC	Silica-based	Solvent under pressure	Multiple mechanisms

Paper Chromatography

Simple, inexpensive technique using cellulose paper as the stationary phase.
Mobile phase (solvent) moves by capillary action.
Used to separate amino acids, sugars, vitamins.
Rf = distance traveled by substance / distance traveled by solvent.

Thin Layer Chromatography (TLC)

Stationary phase is silica gel or alumina coated on a glass/aluminium plate.
Faster and more sensitive than paper chromatography.
Substances are visualized under UV light or with spray reagents (e.g., ninhydrin for amino acids).
Applications: lipid analysis, drug screening, steroid profiling.

Ion-Exchange Chromatography

Uses resins with charged groups (cation exchange = negative resin; anion exchange = positive resin).
Separates molecules based on charge; used for amino acid analysis, protein purification.

Gel Filtration (Size-Exclusion)

Porous beads (e.g., Sephadex) separate molecules by size — small molecules enter pores and elute later; large molecules elute first.
Used for protein purification and molecular weight estimation.

Affinity Chromatography

Most specific technique; uses a ligand (e.g., antibody, enzyme substrate) bound to a matrix.
Used for protein purification (e.g., insulin, enzymes, monoclonal antibodies).

Applications in Biochemical Analysis

Separation and identification of amino acids, lipids, sugars
Purification of proteins and enzymes
Drug analysis and toxicology screening
Separation of nucleotides, vitamins, hormones
Clinical diagnosis (e.g., HbA1c by ion-exchange HPLC)

Q3. Define mutation. Classify different types of mutations and discuss their significance in human diseases

Definition A mutation is a permanent, heritable change in the nucleotide sequence of DNA that can alter gene function. Mutations may arise spontaneously (errors in DNA replication) or be induced by mutagens (radiation, chemicals).

Classification

A. Point Mutations — change in a single base pair

Subtype	Description	Example	Disease
Silent	Codon changes but same amino acid encoded (degeneracy of genetic code)	CGA → CGG (both = Arg)	Usually no disease; rare splice-site effects (e.g., Hutchinson-Gilford Progeria)
Missense	Different amino acid substituted	GAG → GTG (Glu → Val)	Sickle cell anemia (β-globin E6V)
Nonsense	Stop codon introduced; premature chain termination	CGA → UGA (Arg → Stop)	β-thalassemia, Duchenne muscular dystrophy

B. Frameshift Mutations — insertion or deletion of one or more bases (not in multiples of 3) shifts the reading frame of all downstream codons, usually causing a nonfunctional protein. Example: Duchenne muscular dystrophy (deletion in dystrophin gene).

C. Splice-Site Mutations — alter consensus sequences at intron–exon boundaries, causing defective mRNA splicing. Example: β-thalassemia.

D. Chromosomal Mutations — large-scale changes:

Deletion — loss of a chromosomal segment (e.g., cri-du-chat syndrome)
Duplication — extra copy of a segment
Inversion — segment reversed (e.g., hemophilia A)
Translocation — segment moves to another chromosome (e.g., Philadelphia chromosome in CML: t(9;22))

E. Trinucleotide Repeat Expansions — unstable repetitions of 3-nucleotide sequences. Examples: Huntington disease (CAG repeats in HTT gene), Fragile X syndrome (CGG in FMR1).

Significance in Human Diseases

Oncogenes / tumor suppressor mutations → cancer (e.g., p53, BRCA1, RAS mutations)
Inborn errors of metabolism (e.g., PKU — PAH gene; albinism — TYR gene)
Hemoglobinopathies — sickle cell anemia, thalassemias
Immunodeficiency — mutations in ADA (adenosine deaminase) → SCID
Pharmacogenomics — mutations in CYP450 genes affect drug metabolism

Q4. Describe the process of transcription in prokaryotes with suitable diagrams

Definition Transcription is the process by which the DNA template strand is read by RNA polymerase to synthesize a complementary RNA molecule (mRNA, tRNA, or rRNA). It is the first step in gene expression.

Key Enzyme: RNA Polymerase (Prokaryotes) Prokaryotes have a single RNA polymerase composed of subunits (α₂ββ'ω = core enzyme). The sigma (σ) factor associates with the core to form the holoenzyme, which recognizes and binds to promoters. Different sigma factors recognize different classes of genes.

Stages of Transcription

1. Initiation

The holoenzyme (α₂ββ'ωσ) scans the DNA and binds to the promoter — a specific sequence upstream of the gene.
In E. coli, the key promoter elements are:
- Pribnow box (−10 region): consensus sequence TATAAT — recognized by the σ factor.
- −35 region: consensus sequence TTGACA.
The σ factor causes local unwinding of DNA (forming an open complex), and RNA synthesis begins at the +1 (start) site.
The first nucleotide is usually a purine (A or G).
RNA polymerase synthesizes RNA 5'→3', reading the template strand 3'→5'.

2. Elongation

The σ factor dissociates; the core enzyme moves along the DNA.
Ribonucleoside triphosphates (ATP, GTP, CTP, UTP) are incorporated, with pyrophosphate released with each addition.
A transcription bubble (∼17 bp) moves with the polymerase as upstream DNA re-anneals.
RNA is synthesized complementarily to the template (coding/non-template strand = same sequence as RNA, except T→U).

3. Termination Two mechanisms:

Rho-independent (intrinsic) termination: The RNA forms a GC-rich hairpin loop followed by a run of U residues. The hairpin destabilizes the RNA–DNA hybrid, releasing the RNA.
Rho-dependent termination: The Rho protein (a helicase) binds a rut (Rho utilization) site on the RNA and tracks along until it reaches a paused polymerase at a termination site, then unwinds the RNA–DNA hybrid.

Product The RNA produced is a primary transcript (pre-mRNA in eukaryotes). In prokaryotes, translation begins even before transcription is complete (coupled transcription–translation).

Differences from Eukaryotic Transcription (brief note)

Prokaryotes: one RNA polymerase, no nucleus, coupled with translation, no post-transcriptional processing needed before translation.
Eukaryotes: three RNA polymerases (I, II, III), transcription in nucleus, extensive post-transcriptional modifications (5' cap, 3' poly-A tail, splicing of introns).

SHORT ANSWER QUESTIONS

1. Glass Electrode in pH Meter

The glass electrode consists of a thin glass bulb (made of special pH-sensitive glass) at its tip, filled with 0.1 M HCl. An internal reference electrode (Ag/AgCl wire) is immersed in this solution. The glass membrane selectively allows H⁺ to exchange, generating a potential proportional to the external H⁺ activity. The voltage produced follows the Nernst equation and is proportional to the pH of the test solution.

2. Buffer Solutions Used in pH Meter Calibration

Standard buffers used:

pH 4.00 — potassium hydrogen phthalate (acid buffer)
pH 7.00 — phosphate buffer (neutral reference)
pH 9.18 / 10.01 — borax buffer (alkaline buffer)

Two-point calibration (e.g., pH 4.0 and pH 7.0) corrects both offset and slope of the electrode response.

3. Paper Chromatography

A separation technique using cellulose paper as the stationary phase (water held within cellulose fibers) and an organic solvent as the mobile phase. The sample is spotted at the origin, and the solvent ascends by capillary action, carrying solutes at rates proportional to their solubility in the mobile phase vs. affinity for water. Rf values identify substances. Used to separate amino acids, sugars, nucleotides, and vitamins.

4. Thin Layer Chromatography (TLC)

TLC uses a thin layer of silica gel or alumina coated on a rigid plate as the stationary phase. Separation is primarily by adsorption. It is faster, more sensitive, and gives sharper spots than paper chromatography. Spots are detected by UV fluorescence or chemical sprays. Used for lipids, steroids, drugs, and pigments.

6. Point Mutation

A point mutation is a change in a single nucleotide base in the DNA sequence. It can be:

Silent — same amino acid encoded
Missense — different amino acid (e.g., Glu→Val in sickle cell anemia)
Nonsense — stop codon introduced, truncating the protein

7. Central Dogma

The central dogma of molecular biology states:

DNA → (Transcription) → RNA → (Translation) → Protein

Additionally, reverse transcription (RNA → DNA, by retroviruses) and RNA replication (RNA → RNA, by RNA viruses) are recognized exceptions. DNA can also replicate to produce daughter DNA molecules.

8. RNA Polymerase

RNA polymerase is the enzyme responsible for transcribing DNA into RNA. In prokaryotes, one type of RNA polymerase (with subunits α₂ββ'ω + σ factor) transcribes all RNA classes. In eukaryotes:

RNA Pol I → rRNA (28S, 18S, 5.8S)
RNA Pol II → mRNA (protein-coding genes) + snRNA
RNA Pol III → tRNA, 5S rRNA, small RNAs

RNA polymerase does not require a primer and synthesizes RNA 5'→3'.

9. Post-Transcriptional Modifications

In eukaryotes, the primary RNA transcript (pre-mRNA, hnRNA) undergoes processing before becoming mature mRNA:

5' Capping — addition of 7-methylguanosine cap at the 5' end; protects mRNA from degradation, aids ribosome binding.
3' Polyadenylation — addition of 150–250 adenine residues (poly-A tail) to the 3' end; increases mRNA stability.
Splicing — removal of introns (non-coding sequences) and joining of exons by spliceosomes.
RNA editing — rare modification of specific bases in mRNA (e.g., apolipoprotein B).

10. Differences Between Replication and Transcription

Feature	DNA Replication	Transcription
Template	Both strands	Only template (antisense) strand
Product	DNA	RNA
Enzyme	DNA polymerase	RNA polymerase
Primer needed	Yes	No
Nucleotides used	dNTPs (dATP, dGTP, dCTP, dTTP)	NTPs (ATP, GTP, CTP, UTP)
Extent	Entire genome	Specific gene segments
Occurs	S phase of cell cycle	G1, G2, S phase (continuously)
Fidelity	Very high (proofreading)	Lower (errors tolerated)

ONE-LINER / VIVA QUESTIONS

1. What is pH?

pH = −log[H⁺]. It is a measure of the hydrogen ion concentration (activity) of a solution. pH 7 is neutral; < 7 is acidic; > 7 is alkaline.

2. Name the electrode commonly used in a pH meter.

Glass electrode (for H⁺ measurement) and calomel or Ag/AgCl reference electrode. Modern meters often combine both in a single combination electrode.

3. Which chromatography technique is used for protein purification?

Affinity chromatography is the most specific and efficient method for protein purification, exploiting the specific binding of a protein to an immobilized ligand (e.g., antigen-antibody, enzyme-substrate interactions). Ion-exchange chromatography and gel filtration are also widely used.

5. Define mutation.

A mutation is a permanent heritable change in the base sequence of DNA that alters genetic information. It may or may not affect the phenotype depending on the nature and location of the change.

6. What is a silent mutation?

A silent (synonymous) mutation is a point mutation in which the base change does not alter the amino acid sequence of the protein, because the new codon still codes for the same amino acid (due to degeneracy of the genetic code). Example: CGA → CGG both encode Arginine.

7. Name the enzyme involved in transcription.

RNA polymerase. In prokaryotes, one multimeric RNA polymerase handles all transcription. In eukaryotes, RNA polymerase II is responsible for mRNA synthesis.

8. Which RNA carries amino acids to ribosomes?

Transfer RNA (tRNA). Each tRNA has an anticodon that recognizes the corresponding mRNA codon, and carries the appropriate amino acid at its 3' CCA terminus to the ribosome during translation.

9. What is the first step of transcription called?

Initiation — when RNA polymerase holoenzyme binds to the promoter region of DNA, unwinds the double helix (open complex), and begins synthesizing the RNA chain at the +1 start site.

10. Name the RNA synthesized during transcription.

mRNA (messenger RNA) — carries the genetic code from DNA to ribosomes.
tRNA (transfer RNA) — adaptor molecule for translation.
rRNA (ribosomal RNA) — structural and catalytic component of ribosomes.
snRNA, hnRNA, miRNA and other non-coding RNAs are also transcription products.

The primary transcript is called heterogeneous nuclear RNA (hnRNA) in eukaryotes, which is processed into mature mRNA.

Sources: Basic Medical Biochemistry – A Clinical Approach 6e (Lippincott); Guyton & Hall Textbook of Medical Physiology; Tietz Textbook of Laboratory Medicine 7e; Lippincott's Illustrated Reviews: Biochemistry 8e.

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