Q.1 Which of the following amino acids is essential in humans?
Glycine
Alanine
Leucine
Glutamine
Explanation - Leucine is an essential amino acid, meaning it cannot be synthesized by the human body and must be obtained from the diet.
Correct answer is: Leucine
Q.2 What is the primary site for amino acid catabolism in the human body?
Kidney
Liver
Muscle
Pancreas
Explanation - The liver is the main site for amino acid breakdown, including deamination and urea synthesis.
Correct answer is: Liver
Q.3 Which enzyme catalyzes the first step in amino acid degradation?
Transaminase
Urease
Amylase
Lipase
Explanation - Transaminases (or aminotransferases) catalyze the transfer of amino groups from amino acids to α-ketoglutarate, forming glutamate.
Correct answer is: Transaminase
Q.4 The nitrogen from amino acid catabolism is primarily excreted as:
Ammonia
Urea
Uric acid
Creatinine
Explanation - In humans, excess nitrogen from amino acids is converted into urea in the liver and excreted via urine.
Correct answer is: Urea
Q.5 Which amino acid is the main nitrogen donor for the urea cycle?
Glutamine
Glutamate
Aspartate
Alanine
Explanation - Aspartate provides one of the nitrogen atoms that enter the urea cycle, which is essential for urea synthesis.
Correct answer is: Aspartate
Q.6 Phenylketonuria (PKU) results from a defect in which enzyme?
Phenylalanine hydroxylase
Tyrosine aminotransferase
Homogentisate oxidase
Ornithine transcarbamylase
Explanation - PKU is caused by a deficiency of phenylalanine hydroxylase, leading to accumulation of phenylalanine.
Correct answer is: Phenylalanine hydroxylase
Q.7 Which amino acid is glucogenic but not ketogenic?
Leucine
Lysine
Alanine
Phenylalanine
Explanation - Alanine can be converted into pyruvate and subsequently glucose, making it purely glucogenic.
Correct answer is: Alanine
Q.8 Which amino acid is both glucogenic and ketogenic?
Leucine
Lysine
Isoleucine
Methionine
Explanation - Isoleucine can be broken down into both acetyl-CoA (ketogenic) and succinyl-CoA (glucogenic) intermediates.
Correct answer is: Isoleucine
Q.9 What is the primary function of transamination reactions?
Convert ammonia to urea
Transfer amino groups to α-keto acids
Break peptide bonds
Synthesize fatty acids
Explanation - Transamination transfers the amino group from an amino acid to an α-keto acid, forming a new amino acid and α-keto acid.
Correct answer is: Transfer amino groups to α-keto acids
Q.10 Which compound is a common α-keto acid acceptor in transamination?
α-Ketoglutarate
Pyruvate
Oxaloacetate
All of the above
Explanation - α-Ketoglutarate, pyruvate, and oxaloacetate all act as amino group acceptors in different transamination reactions.
Correct answer is: All of the above
Q.11 Urea cycle occurs primarily in which cellular compartment?
Cytosol
Mitochondria
Both mitochondria and cytosol
Endoplasmic reticulum
Explanation - The urea cycle begins in the mitochondria and is completed in the cytosol.
Correct answer is: Both mitochondria and cytosol
Q.12 Which amino acid serves as a precursor for neurotransmitter synthesis?
Tryptophan
Glycine
Proline
Serine
Explanation - Tryptophan is converted into serotonin, an important neurotransmitter.
Correct answer is: Tryptophan
Q.13 Which amino acid is exclusively ketogenic?
Leucine
Isoleucine
Phenylalanine
Tyrosine
Explanation - Leucine is broken down into acetyl-CoA and acetoacetate and cannot be converted into glucose.
Correct answer is: Leucine
Q.14 Maple syrup urine disease is caused by a defect in metabolism of:
Branched-chain amino acids
Aromatic amino acids
Sulfur-containing amino acids
All amino acids
Explanation - It is caused by defective branched-chain α-keto acid dehydrogenase, leading to accumulation of leucine, isoleucine, and valine.
Correct answer is: Branched-chain amino acids
Q.15 Which coenzyme is required for transaminase activity?
NAD+
FAD
Pyridoxal phosphate (PLP)
Coenzyme A
Explanation - PLP, derived from vitamin B6, serves as a coenzyme in transamination reactions.
Correct answer is: Pyridoxal phosphate (PLP)
Q.16 Which amino acid is a key nitrogen transporter in the blood?
Glutamine
Arginine
Cysteine
Lysine
Explanation - Glutamine carries ammonia safely in the blood to the liver and kidneys.
Correct answer is: Glutamine
Q.17 Which enzyme converts ammonia and CO2 into carbamoyl phosphate in the urea cycle?
Carbamoyl phosphate synthetase I
Ornithine transcarbamylase
Arginase
Argininosuccinate synthetase
Explanation - This is the rate-limiting step of the urea cycle, occurring in mitochondria.
Correct answer is: Carbamoyl phosphate synthetase I
Q.18 Excess dietary amino acids are primarily converted to:
Glucose or fatty acids
Ketone bodies
Uric acid
None of the above
Explanation - Excess amino acids are deaminated and their carbon skeletons enter gluconeogenesis or lipogenesis pathways.
Correct answer is: Glucose or fatty acids
Q.19 Which amino acid is a precursor for nitric oxide synthesis?
Arginine
Citrulline
Glutamate
Histidine
Explanation - Nitric oxide synthase converts arginine into nitric oxide and citrulline.
Correct answer is: Arginine
Q.20 Glucogenic amino acids can be converted into:
Acetyl-CoA
Pyruvate or TCA cycle intermediates
Ketone bodies only
Cholesterol
Explanation - Glucogenic amino acids are converted into substrates for gluconeogenesis.
Correct answer is: Pyruvate or TCA cycle intermediates
Q.21 Which enzyme deficiency leads to hyperammonemia?
Ornithine transcarbamylase
Arginase
Phenylalanine hydroxylase
Branched-chain α-ketoacid dehydrogenase
Explanation - OTC deficiency blocks the urea cycle, causing ammonia accumulation in the blood.
Correct answer is: Ornithine transcarbamylase
Q.22 Which amino acid is used for creatine synthesis in muscle?
Arginine
Methionine
Glycine
All of the above
Explanation - Creatine synthesis requires arginine, glycine, and methylation by methionine.
Correct answer is: All of the above
Q.23 Which amino acid is a sulfur donor for cysteine synthesis?
Methionine
Serine
Tryptophan
Tyrosine
Explanation - Methionine provides sulfur for the synthesis of cysteine via the transsulfuration pathway.
Correct answer is: Methionine
Q.24 Ammonia detoxification in the brain primarily occurs via:
Glutamate dehydrogenase
Glutamine synthetase
Urease
Transaminase
Explanation - Glutamine synthetase in astrocytes converts ammonia and glutamate into glutamine, reducing neurotoxicity.
Correct answer is: Glutamine synthetase
Q.25 Which amino acid degradation produces fumarate as an intermediate?
Phenylalanine
Leucine
Lysine
Valine
Explanation - Phenylalanine is converted to tyrosine, eventually producing fumarate and acetoacetate.
Correct answer is: Phenylalanine