---

Your Complete Clinical Biochemistry Exam Notes are Ready!

---

---

UNIT VI — NUCLEIC ACID METABOLISM (10 Marks)

Key Points

• Nucleotide = Nitrogenous Base + Pentose Sugar + Phosphate group
• Purines (A, G) = double ring; Pyrimidines (C, T, U) = single ring
• Catabolism: Purines → Uric acid | Pyrimidines → CO2 + NH3 + Beta-alanine

De Novo Purine Synthesis Flowchart

Ribose-5-P (HMP shunt)
       ↓
    PRPP (PRPP synthetase)
       ↓
    PRA (amidoPRTase — RATE-LIMITING STEP)
       ↓
   10 more steps (Gly, Gln, Asp, CO2, Formate)
       ↓
    IMP (Inosine Monophosphate) — 1st purine
       ↓              ↓
   AMP (2 steps)   GMP (2 steps)
       ↓              ↓
   ATP            GTP → DNA/RNA

De Novo Pyrimidine Synthesis Flowchart

CO2 + Glutamine + ATP → Carbamoyl phosphate (CPS II — cytoplasmic)
       ↓
Carbamoyl phosphate + Aspartate
       ↓
   Dihydroorotate → Orotate
       ↓
   Orotate + PRPP → OMP
       ↓
   OMP → UMP (1st pyrimidine nucleotide)
       ↓           ↓
   UTP → CTP     dUDP → dTMP

Salvage Pathway

DNA Replication (Semi-Conservative)

Helicase (unwinds) → SSB proteins (stabilize) → Primase (RNA primer)
→ DNA Pol III [Leading strand: continuous | Lagging strand: Okazaki fragments]
→ DNA Pol I (removes primers) → DNA Ligase (seals) → 2 daughter DNA molecules

---

UNIT VII — INTRODUCTION TO CLINICAL CHEMISTRY (10 Marks)

Kidney Function

• GFR = 125 mL/min; measured by Creatinine Clearance
• Formula: Clearance = (Urine Creatinine × Urine Volume) / Serum Creatinine
• Normal: 80-120 mL/min

NPN (Non-Protein Nitrogen) Constituents

Abnormal Urine Findings

Urinary Stones (Calculi)

• Calcium Oxalate (80%) — most common, hard, radiopaque
• Uric Acid — radiolucent (invisible on X-ray), associated with gout
• Cystine — rare, cystinuria (amino acid transport defect)

---

UNIT VIII — LIVER FUNCTION TESTS (10 Marks)

Functions of Liver — Mnemonic: MEDS-PC

• Metabolism (glucose, protein, lipid)
• Excretion (bilirubin, bile)
• Detoxification (ammonia → urea, drugs)
• Synthesis (albumin, clotting factors I, II, V, VII, IX, X)
• Production (bile acids from cholesterol)
• Conjugation (bilirubin + glucuronic acid)

Bilirubin Metabolism Flowchart

Haemoglobin (RBC breakdown)
       ↓
Haem → Biliverdin → Unconjugated Bilirubin (indirect, fat-soluble, TOXIC)
       ↓ binds Albumin → transported to liver
Liver: UDP-glucuronyltransferase
       ↓
Conjugated Bilirubin (direct, water-soluble) → secreted into bile
       ↓ intestine
Urobilinogen → Stercobilin (brown stool) | some reabsorbed → Urobilin (yellow urine)

3 Types of Jaundice

SGOT vs SGPT

• SGPT (ALT) = Alanine Aminotransferase = liver-specific (most sensitive)
• SGOT (AST) = found in liver, heart, muscle, kidney
• De Ritis Ratio = AST/ALT: >2 = alcoholic liver disease; <1 = viral hepatitis

---

UNIT IX — LIPID PROFILE TESTS (10 Marks)

Lipoproteins Table

Total Cholesterol — Liebermann-Burchard Method

Serum + Acetic Anhydride + H2SO4
       ↓
Green colour develops
       ↓
Read at 620 nm → Calculate from standard curve
Normal: <200 mg/dL

LDL Calculation — Friedewald Formula

LDL = Total Cholesterol - HDL - (Triglycerides / 5)
Valid only when TG <400 mg/dL

RIA (Radioimmunoassay)

Labelled Ag* + Unknown Ag + Limited Ab
       ↓ Competition for binding
Ag*-Ab (bound) separated from free Ag*
       ↓
Measure radioactivity (Gamma counter)
More Ag in sample → Less Ag* bound → Less radioactivity → Higher concentration

• Advantage: Extremely sensitive (detects picograms), highly specific
• Disadvantage: Radioactive hazard, expensive, short shelf life

ELISA (Sandwich Type)

Ab1 coated on microtitre plate
       ↓ + Patient sample
Ag binds Ab1 (wash)
       ↓ + Enzyme-linked Ab2
Sandwich formed (wash)
       ↓ + Substrate (TMB)
Coloured product → Stop with H2SO4
       ↓
Read absorbance at 450 nm → Concentration

• Advantage: No radioactivity, safe, cheap, automated

---

UNIT X — ELECTROLYTES (10 Marks)

Body Fluid Compartments

Normal Values (Memory Trick: 135-145-95-3.5-5)

• Na+ = 135-145 mEq/L
• K+ = 3.5-5.0 mEq/L
• Cl- = 95-105 mEq/L

Aldosterone / RAAS Flowchart

Low BP / Low Na+ → Kidney JG cells → Renin
       ↓
Angiotensinogen → Angiotensin I → (ACE) → Angiotensin II
       ↓
Adrenal cortex → Aldosterone
       ↓
DCT/CD: ↑ Na+ reabsorption + ↑ K+ excretion + Water retention
       ↓
BP and ECF volume restored

Hyponatraemia vs Hypernatraemia

ORS Composition (WHO)

• NaCl + KCl + Sodium Citrate + Glucose (drives Na+ absorption in gut)

---

PDF includes:

• Color-coded flowcharts for every pathway
• Complete tables for every topic
• Exam answer templates showing exactly how to score all 10 marks per question
• Full-page MIND MAP comparing all 5 units side by side
• Last-Minute Summary Table at the end