Biochemist - Category Number 232/2024

Sample Questions

Question 1

Q: Which type of chromatography is most suitable for separating small polar biomolecules such as amino acids and sugars?

Answer: Ion-exchange chromatography (particularly anion or cation exchange depending on molecule charge) or HPLC with appropriate polar stationary phase; for many small polar molecules, ion-exchange is commonly used.

Question 2

Q: Describe the Michaelis–Menten constant (Km) and its significance in enzyme kinetics.

Answer: Km is the substrate concentration at which the reaction rate is half of Vmax. It reflects the affinity of the enzyme for its substrate (lower Km = higher affinity) under Michaelis–Menten conditions.

Question 3

Q: What is the primary clinical significance of elevated serum alanine aminotransferase (ALT)?

Answer: Elevated ALT is primarily a marker of hepatocellular injury or liver cell damage and is commonly used to assess liver disease or acute hepatic injury.

Question 4

Q: Name two quality control measures commonly used in clinical laboratories to ensure reliability of test results.

Answer: Internal quality control (use of control samples with known values run with patient samples) and external quality assessment (proficiency testing schemes where labs are sent blinded samples to evaluate performance).

Question 5

Q: Explain the basic principle of polymerase chain reaction (PCR).

Answer: PCR amplifies a specific DNA sequence through repeated cycles of denaturation, annealing of primers, and extension by a thermostable DNA polymerase, producing exponential copies of the target sequence.

Question 6

Q: A patient’s lab report shows an unexpectedly high creatinine value. List three pre-analytical factors that could falsely elevate the result.

Answer: Hemoconcentration from prolonged tourniquet use, delayed sample separation (cells leaking substances), and ingestion of interfering substances or drugs (e.g., cephalosporins in some assays) can falsely affect measured creatinine.

Question 7

Q: Identify the main structural information each technique provides: NMR and mass spectrometry.

Answer: NMR provides detailed information about molecular structure, chemical environment of atoms, and stereochemistry; mass spectrometry provides accurate molecular mass, elemental composition, and fragmentation patterns useful for identifying and characterizing molecules.

Question 8

Q: Briefly explain first-order versus zero-order kinetics in pharmacokinetics.

Answer: First-order kinetics means the rate of drug elimination is proportional to its concentration (a constant fraction is eliminated per unit time). Zero-order kinetics means a constant amount of drug is eliminated per unit time regardless of concentration (e.g., high-dose ethanol or phenytoin at saturating levels).

Question 9

Q: In clinical enzymology, why is the measurement of troponin preferred over CK-MB for diagnosing acute myocardial infarction?

Answer: Cardiac troponins (I and T) are more specific and sensitive for myocardial injury, they remain elevated longer than CK-MB, and they have lower false-positive rates from non-cardiac muscle injury.

Question 10

Q: What is the role of allosteric regulation in enzyme activity? Give one example.

Answer: Allosteric regulation modulates enzyme activity through binding of effectors at sites other than the active site, causing conformational changes that increase or decrease activity. Example: Phosphofructokinase-1 (PFK-1) is activated by AMP and inhibited by ATP/citrate in glycolysis regulation.

Question 11

Q: What is the main buffer system of human blood, and what is its normal physiological pH range?

Answer: The bicarbonate buffer system (HCO₃⁻/H₂CO₃) is the primary buffer of blood. Normal blood pH is maintained between 7.35 and 7.45.

Question 12

Q: Name the coenzyme required by transaminases (aminotransferases) for catalytic activity.

Answer: Pyridoxal phosphate (PLP), the active form of vitamin B6, is required as a coenzyme by aminotransferases.

Question 13

Q: Which laboratory test is commonly used as a marker of long-term glucose control in diabetic patients?

Answer: Glycated hemoglobin (HbA1c) is used as a marker for average blood glucose control over the past 2–3 months.

Question 14

Q: In electrophoresis, what is the basis of separation of biomolecules?

Answer: Molecules are separated based on their charge-to-mass ratio and size as they migrate in an electric field through a supporting medium.

Question 15

Q: Which plasma protein is most important in maintaining colloid osmotic pressure?

Answer: Albumin is the major plasma protein responsible for maintaining colloid osmotic pressure.

Question 16

Q: What is the biochemical basis of jaundice?

Answer: Jaundice occurs due to accumulation of bilirubin in the blood, caused by excessive production (hemolysis), impaired conjugation (liver disease), or obstruction of bile flow.

Question 17

Q: What is the principle behind ELISA (Enzyme-Linked Immunosorbent Assay)?

Answer: ELISA uses antigen-antibody specificity combined with an enzyme-linked secondary antibody that produces a detectable signal (usually color change) upon reaction with a substrate.

Question 18

Q: Which vitamin deficiency causes scurvy, and what is the biochemical reason?

Answer: Vitamin C deficiency causes scurvy due to impaired hydroxylation of proline and lysine in collagen synthesis, leading to defective connective tissue.

Question 19

Q: State one key difference between competitive and non-competitive enzyme inhibition.

Answer: In competitive inhibition, the inhibitor binds to the active site, increasing Km but not affecting Vmax. In non-competitive inhibition, the inhibitor binds to a different site, reducing Vmax without changing Km.

Question 20

Q: What is the clinical importance of measuring serum lactate levels?

Answer: Elevated serum lactate indicates lactic acidosis, which may occur in shock, hypoxia, sepsis, or mitochondrial dysfunction, and helps assess tissue oxygenation status.

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