Transamination MCQs With Answer — Master the core concepts of transamination essential for B.Pharm students studying amino acid metabolism, enzymology and clinical biochemistry. This concise, keyword-rich introduction covers aminotransferases (transaminases), the vital cofactor pyridoxal phosphate (PLP), reaction mechanisms, role in nitrogen transfer and links to the urea cycle and gluconeogenesis. Understanding transamination is critical for interpreting liver function tests (ALT/AST), drug effects on vitamin B6-dependent enzymes, and metabolic pathways of non-essential amino acid synthesis. Clear explanations and practice questions will help you retain mechanism details, tissue distribution, clinical relevance and experimental inhibitors. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the primary chemical change in a transamination reaction?
- Transfer of a carboxyl group between two amino acids
- Transfer of an amino group between an amino acid and an α-keto acid
- Removal of ammonia as free NH3 from amino acids
- Oxidation of the amino acid side chain
Correct Answer: Transfer of an amino group between an amino acid and an α-keto acid
Q2. Which cofactor is absolutely required for aminotransferase (transaminase) activity?
- Thiamine pyrophosphate (TPP)
- Pyridoxal 5′-phosphate (PLP)
- Flavin adenine dinucleotide (FAD)
- Biotin
Correct Answer: Pyridoxal 5′-phosphate (PLP)
Q3. Aminotransferases are commonly known by which other name?
- Dehydrogenases
- Transaminases
- Hydrolases
- Isomerases
Correct Answer: Transaminases
Q4. Alanine aminotransferase (ALT) catalyzes which reaction?
- Alanine + pyruvate → oxaloacetate + glutamate
- Alanine + α-ketoglutarate → pyruvate + glutamate
- Alanine + oxaloacetate → pyruvate + aspartate
- Alanine + α-ketoglutarate → oxaloacetate + glutamine
Correct Answer: Alanine + α-ketoglutarate → pyruvate + glutamate
Q5. Aspartate aminotransferase (AST) converts aspartate and α-ketoglutarate into which pair of products?
- Alanine and oxaloacetate
- Glutamate and oxaloacetate
- Glutamate and pyruvate
- Glutamine and malate
Correct Answer: Glutamate and oxaloacetate
Q6. During the PLP-dependent mechanism, PLP initially forms what type of bond with the enzyme?
- Peptide bond with an active site serine
- Carbamate linkage with CO2
- Schiff base (internal aldimine) with an active site lysine
- Disulfide bond with a cysteine residue
Correct Answer: Schiff base (internal aldimine) with an active site lysine
Q7. Which kinetic mechanism characterizes most transaminase-catalyzed reactions?
- Ordered sequential
- Random sequential
- Ping-pong (double displacement)
- Single displacement
Correct Answer: Ping-pong (double displacement)
Q8. Which α-keto acid is the most common amino-group acceptor in transamination reactions of amino acid catabolism?
- Oxaloacetate
- Pyruvate
- α-Ketoglutarate
- Succinyl-CoA
Correct Answer: α-Ketoglutarate
Q9. In the alanine cycle, which amino acid transports nitrogen from muscle to liver?
- Glutamine
- Alanine
- Leucine
- Glycine
Correct Answer: Alanine
Q10. Where is alanine aminotransferase (ALT) predominantly localized in hepatocytes?
- Mitochondrial matrix
- Cytosol
- Lysosome
- Golgi apparatus
Correct Answer: Cytosol
Q11. Clinically, an isolated significant rise in ALT is most suggestive of which condition?
- Cardiac infarction
- Renal failure
- Hepatocellular injury
- Muscle hypertrophy
Correct Answer: Hepatocellular injury
Q12. An AST:ALT ratio greater than 2 is classically associated with which etiology?
- Viral hepatitis
- Ischemic hepatitis
- Alcoholic liver disease
- Autoimmune hepatitis
Correct Answer: Alcoholic liver disease
Q13. Pyridoxine (vitamin B6) deficiency affects transamination because it reduces levels of which active cofactor?
- NAD+
- Pyridoxal 5′-phosphate (PLP)
- Tetrahydrofolate
- Coenzyme A
Correct Answer: Pyridoxal 5′-phosphate (PLP)
Q14. Which amino acid is classically resistant to transamination due to its side chain structure?
- Alanine
- Lysine
- Serine
- Leucine
Correct Answer: Lysine
Q15. Transamination reactions contribute directly to the biosynthesis of which non-essential amino acids?
- Cysteine and methionine
- Alanine, aspartate and glutamate
- Lysine and histidine
- Phenylalanine and tyrosine
Correct Answer: Alanine, aspartate and glutamate
Q16. Which two interchangeable coenzyme forms are involved in aminotransferase catalysis?
- FMN and FAD
- PLP and PMP (pyridoxamine phosphate)
- ATP and ADP
- CoA and acetyl-CoA
Correct Answer: PLP and PMP (pyridoxamine phosphate)
Q17. The internal aldimine (enzyme-PLP) is converted to an external aldimine during catalysis by reaction with which group?
- Carboxyl group of the substrate
- Amino group of the substrate amino acid
- Side chain hydroxyl of serine
- Terminal phosphate of ATP
Correct Answer: Amino group of the substrate amino acid
Q18. Which compound is a commonly used experimental inhibitor of PLP-dependent transaminases?
- Allopurinol
- Aminooxyacetate (AOA)
- EDTA
- Atropine
Correct Answer: Aminooxyacetate (AOA)
Q19. When glutamate donates its amino group in transamination, which α-keto acid commonly accepts it to form aspartate?
- Pyruvate
- Oxaloacetate
- Acetoacetate
- Fumarate
Correct Answer: Oxaloacetate
Q20. How does transamination link to the urea cycle?
- Transamination removes carbamoyl phosphate
- Transamination generates aspartate which supplies a nitrogen for urea synthesis
- Transamination directly converts ammonia to urea
- Transamination produces argininosuccinate which becomes urea
Correct Answer: Transamination generates aspartate which supplies a nitrogen for urea synthesis
Q21. Which aminotransferase reaction directly provides pyruvate for gluconeogenesis during fasting?
- Glutamate aminotransferase
- Alanine aminotransferase (ALT)
- Aspartate aminotransferase (AST)
- Branched-chain amino acid transaminase (BCAT)
Correct Answer: Alanine aminotransferase (ALT)
Q22. Which statement correctly describes the subcellular distribution of AST isoenzymes?
- All AST is exclusively cytosolic
- There are cytosolic and mitochondrial isoenzymes of AST
- AST is only found in the endoplasmic reticulum
- AST is localized to the nucleus
Correct Answer: There are cytosolic and mitochondrial isoenzymes of AST
Q23. Which amino acid is produced when α-ketoglutarate accepts an amino group during transamination?
- Glutamate
- Alanine
- Aspartate
- Proline
Correct Answer: Glutamate
Q24. The direction of a transaminase-catalyzed reaction in vivo is primarily determined by what factor?
- Temperature only
- pH only
- Relative concentrations of substrates and products (mass action)
- Presence of oxygen
Correct Answer: Relative concentrations of substrates and products (mass action)
Q25. Many clinical assays for transaminase activity rely on monitoring which cofactor in a coupled reaction?
- NADH/NAD+
- ATP/ADP
- CoA
- FADH2/FAD
Correct Answer: NADH/NAD+
Q26. Branched-chain aminotransferase (BCAT) activity is highest in which tissue, reflecting branched-chain amino acid catabolism?
- Liver
- Skeletal muscle
- Pancreas
- Adipose tissue
Correct Answer: Skeletal muscle
Q27. What is the immediate biochemical fate of the amino group transferred to α-ketoglutarate during transamination?
- It is released as free ammonia immediately
- It is incorporated into glutamate
- It is converted to urea directly
- It is attached to pyruvate to form alanine
Correct Answer: It is incorporated into glutamate
Q28. Under the EC (Enzyme Commission) classification, aminotransferases are grouped under which main class?
- Oxidoreductases
- Transferases
- Hydrolases
- Lyases
Correct Answer: Transferases
Q29. During prolonged fasting, what is the expected effect on muscle transamination activity supplying alanine for gluconeogenesis?
- Transamination decreases markedly
- Transamination remains unchanged
- Transamination increases to supply alanine
- Transamination is replaced by direct proteolysis only
Correct Answer: Transamination increases to supply alanine
Q30. Why is transamination important for maintaining nitrogen balance in the body?
- It removes carbon skeletons for excretion
- It irreversibly destroys amino groups
- It enables reversible transfer of amino groups for biosynthesis and disposal
- It synthesizes urea directly from amino acids
Correct Answer: It enables reversible transfer of amino groups for biosynthesis and disposal
Q31. During transamination, PLP is converted transiently to which form after accepting an amino group?
- Pyridoxamine phosphate (PMP)
- Thiamine monophosphate (TMP)
- NADP+
- Biotinyl-lysine
Correct Answer: Pyridoxamine phosphate (PMP)
Q32. Which enzyme regenerates α-ketoglutarate from glutamate during oxidative deamination, complementing transamination pathways?
- Glutamate dehydrogenase
- Alanine aminotransferase
- Aspartate aminotransferase
- Glutamine synthetase
Correct Answer: Glutamate dehydrogenase
Q33. Which statement contrasts transamination with oxidative deamination?
- Transamination transfers an amino group; oxidative deamination removes it as ammonia
- Both reactions produce free ammonia directly
- Transamination requires oxygen, oxidative deamination does not
- Oxidative deamination uses PLP as cofactor
Correct Answer: Transamination transfers an amino group; oxidative deamination removes it as ammonia
Q34. A drug that causes vitamin B6 deficiency would most likely have what effect on aminotransferase activities?
- No effect because B6 is not involved
- Decrease aminotransferase activity due to PLP depletion
- Increase aminotransferase activity by inducing enzyme synthesis
- Convert aminotransferases to dehydrogenases
Correct Answer: Decrease aminotransferase activity due to PLP depletion
Q35. Transamination of phenylalanine primarily yields which α-keto acid?
- Phenylpyruvate
- β-Hydroxyphenylpyruvate
- Homogentisate
- Oxaloacetate
Correct Answer: Phenylpyruvate
Q36. The covalent intermediate formed between PLP and substrate during transamination is known as what?
- Internal Schiff base only
- External aldimine
- Carbanion radical
- Enamine complex
Correct Answer: External aldimine
Q37. Which mechanistic feature correctly describes aminotransferase catalysis?
- Substrates bind simultaneously and react in a ternary complex
- The enzyme forms a covalently bound PLP-substrate intermediate and releases a product before the second substrate binds
- It requires molecular oxygen as an electron acceptor
- It phosphorylates substrates using ATP
Correct Answer: The enzyme forms a covalently bound PLP-substrate intermediate and releases a product before the second substrate binds
Q38. What is the stoichiometry of amino group transfer in a single transamination event?
- Two amino groups transferred per reaction
- One amino group transferred per reaction
- Zero amino groups are transferred
- Three amino groups transferred per reaction
Correct Answer: One amino group transferred per reaction
Q39. AST is also commonly abbreviated as which of the following in clinical reports?
- SGPT
- ALT
- SGOT
- ALP
Correct Answer: SGOT
Q40. Which laboratory unit is commonly used to report serum aminotransferase activity?
- mg/dL
- moles/L
- International units per liter (IU/L)
- g/L
Correct Answer: International units per liter (IU/L)
Q41. Which anti-tuberculosis drug is notorious for causing functional PLP deficiency and can secondarily impair transaminases?
- Rifampicin
- Isoniazid
- Ethambutol
- Pyrazinamide
Correct Answer: Isoniazid
Q42. Which amino acid is less likely to undergo classical transamination due to its secondary amine structure?
- Proline
- Glycine
- Valine
- Threonine
Correct Answer: Proline
Q43. How does transamination support neurotransmitter metabolism in the brain?
- By synthesizing dopamine directly from phenylalanine
- By maintaining pools of glutamate and aspartate used as neurotransmitters or precursors
- By converting GABA to glycine
- By producing acetylcholine from serine
Correct Answer: By maintaining pools of glutamate and aspartate used as neurotransmitters or precursors
Q44. Which enzyme catalyzes the oxidative deamination of glutamate to release free ammonia and regenerate α-ketoglutarate?
- Aspartate aminotransferase
- Glutamate dehydrogenase
- Glutamine synthetase
- Alanine aminotransferase
Correct Answer: Glutamate dehydrogenase
Q45. Are transamination reactions reversible under physiological conditions?
- No, they are strictly irreversible
- Yes, they are readily reversible depending on substrate/product concentrations
- They are irreversible unless ATP is present
- They require oxygen to be reversible
Correct Answer: Yes, they are readily reversible depending on substrate/product concentrations
Q46. Which amino acid is synthesized directly from pyruvate by a transamination reaction?
- Aspartate
- Alanine
- Serine
- Glutamine
Correct Answer: Alanine
Q47. Which amino acid is produced by transamination of oxaloacetate?
- Glutamate
- Aspartate
- Alanine
- Tyrosine
Correct Answer: Aspartate
Q48. Which statement best describes substrate specificity of aminotransferases?
- Each aminotransferase acts on only one amino acid and one keto acid exclusively
- Aminotransferases often have preferred substrates but can act on multiple related amino acids and keto acids
- Aminotransferases are non-specific and act on any small organic molecule
- They act only on branched-chain amino acids
Correct Answer: Aminotransferases often have preferred substrates but can act on multiple related amino acids and keto acids
Q49. Which laboratory technique can be used to separate AST isoenzymes (mitochondrial vs cytosolic)?
- Mass spectrometry without separation
- Electrophoresis or isoenzyme electrophoretic separation
- Simple colorimetric assay that cannot distinguish isoenzymes
- PCR amplification of AST mRNA
Correct Answer: Electrophoresis or isoenzyme electrophoretic separation
Q50. Transamination of leucine yields which corresponding α-keto acid?
- α-Ketobutyrate
- α-Ketoisocaproate
- Phenylpyruvate
- Pyruvate
Correct Answer: α-Ketoisocaproate
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
Mail- Sachin@pharmacyfreak.com