Q.1 – Which of the following is a common compound shared by the TCA and Urea cycles?
A) α-Ketoglutarate
B) Succinyl-CoA
C) Oxaloacetate
D) Fumarate
Answer: D) Fumarate
Explanation: Fumarate is a common compound in both the TCA (Tricarboxylic Acid) and urea cycles. In the TCA cycle, fumarate is formed from succinate by the enzyme succinate dehydrogenase. In the urea cycle, fumarate is generated as a by-product of the conversion of argininosuccinate to arginine.
Q.2 – Which of the following is a common nitrogen acceptor for all reactions involving transaminases?
A) α-Keto glutarate
B) Pyruvate
C) Oxaloacetate
D) Acetoacetate
Answer: A) α-Keto glutarate
Explanation: α-Ketoglutarate is a key nitrogen acceptor in amino acid transamination reactions. It accepts an amino group to form glutamate, facilitating the transfer of nitrogen between amino acids and the metabolic pathway.
Q.3 – In a 55-year-old man diagnosed with cirrhosis of the liver, ammonia is not getting detoxified and can damage the brain. Which of the following amino acids can covalently bind ammonia, transport it, and store it in a non-toxic form?
A) Aspartate
B) Glutamate
C) Serine
D) Cysteine
Answer: B) Glutamate
Explanation: Glutamate plays a critical role in ammonia detoxification by binding with ammonia to form glutamine, a process catalyzed by the enzyme glutamine synthetase. This reaction safely stores ammonia in a non-toxic form, which can then be transported to the liver for further processing.
Q.4 – In a newborn presenting with refusal to feed and irritability, a deficiency of Cystathionine β-synthase has been diagnosed. Which of the following compounds is expected to be elevated in blood?
A) Serine
B) Glutamate
C) Homocysteine
D) Valine
Answer: C) Homocysteine
Explanation: Homocysteine levels are expected to be elevated in the blood due to a deficiency in Cystathionine β-synthase, an enzyme crucial for converting homocysteine to cystathionine in the methionine metabolism pathway.
Q.5 – A 3-month-old child is being evaluated for vomiting and an episode of convulsions. Laboratory results show hyperammonemia and orotic aciduria. Which of the following enzyme defects is likely to be there?
A) Glutaminase
B) Arginase
C) Arginosuccinic acid synthase
D) Ornithine Transcarbamoylase
Answer: D) Ornithine Transcarbamoylase
Explanation: Ornithine Transcarbamoylase deficiency is characterized by hyperammonemia and orotic aciduria. This enzyme is crucial in the urea cycle for the conversion of ornithine and carbamoyl phosphate to citrulline, and its deficiency leads to the accumulation of ammonia and orotic acid.
Q.6 – Which of the following amino acids is not converted to Succinyl-CoA?
A) Methionine
B) Valine
C) Isoleucine
D) Histidine
Answer: D) Histidine
Explanation: Histidine is not converted into Succinyl-CoA. Instead, it is metabolized into urocanate and then to formiminoglutamate in the histidine degradation pathway. Methionine, Valine, and Isoleucine, however, are part of the catabolic pathways that lead to the production of Succinyl-CoA.
Q.7 – All of the following compounds are synthesized by transmethylation reactions, except-
A) Choline
B) Epinephrine
C) Creatine
D) Ethanolamine
Answer: D) Ethanolamine
Explanation: Ethanolamine is not typically synthesized by transmethylation reactions. Instead, it is produced by the decarboxylation of serine. Choline, Epinephrine, and Creatine, on the other hand, are all involved in transmethylation processes in various metabolic pathways.
Q.8 – A patient diagnosed with Hartnup disease, which is due to a deficiency of the transporter required for the absorption of amino acid tryptophan, has been brought in with skin rashes and suicidal tendencies. Tryptophan is a precursor for many compounds, the deficiencies of which can cause the said symptoms. Which of the following compounds is not synthesized from tryptophan?
A) Serotonin
B) Epinephrine
C) Melatonin
D) Niacin
Answer: B) Epinephrine
Explanation: Epinephrine is not synthesized from tryptophan but from the amino acid tyrosine. Tryptophan is a precursor for serotonin, melatonin, and niacin, which play roles in mood regulation, sleep, and metabolism, respectively.
Q.9 – Histamine, a chemical mediator of allergies and anaphylaxis, is synthesized from the amino acid Histidine by which of the following processes?
A) Deamination
B) Decarboxylation
C) Transamination
D) Dehydrogenation
Answer: B) Decarboxylation
Explanation: Histamine is formed from Histidine through a decarboxylation reaction catalyzed by the enzyme histidine decarboxylase. This process removes the carboxyl group from Histidine, converting it into histamine.
Q.10 – The synthesis of all of the following compounds except one is deficient in a patient suffering from Phenylketonuria-
A) Melanin
B) Melatonin
C) Catecholamines
D) Thyroid hormone
Answer: C) Melatonin
Explanation: Melatonin synthesis does not involve phenylalanine. Phenylketonuria (PKU) primarily affects the conversion of phenylalanine to tyrosine, which is crucial for the synthesis of melanin, thyroid hormone, and catecholamines.
Q.11 – The diet of a child suffering from Maple syrup urine disease (an amino acid disorder) should be low in which of the following amino acids?
A) Branched-chain amino acids
B) Phenylalanine
C) Methionine
D) Tryptophan
Answer: A) Branched-chain amino acids
Explanation: Maple syrup urine disease is characterized by a deficiency in the enzyme complex responsible for the breakdown of branched-chain amino acids (leucine, isoleucine, and valine). A diet low in these amino acids is essential to manage this condition effectively.
Q.12 – Which of the following amino acids is not required for creatine synthesis?
A) Methionine
B) Serine
C) Glycine
D) Arginine
Answer: B) Serine
Explanation: Creatine synthesis primarily involves the amino acids arginine, glycine, and methionine. Serine does not directly contribute to the synthesis of creatine.
Q.13 – All of the following substances are synthesized from cysteine, except-
A) Taurine
B) Mercaptoethanolamine
C) Melanin
D) Pyruvate
Answer: C) Melanin
Explanation: Melanin is not synthesized from cysteine; it is derived from the amino acid tyrosine. Cysteine is a precursor for substances like taurine and mercaptoethanolamine and plays a role in metabolic pathways leading to products like pyruvate.
Q.14 – Urea is synthesized in –
A) Cytoplasm
B) Mitochondria
C) Both cytoplasm and mitochondria
D) In lysosomes
Answer: C) Both cytoplasm and mitochondria
Explanation: Urea is synthesized in both the mitochondria and the cytoplasm. The urea cycle starts in the mitochondria with the formation of carbamoyl phosphate and then continues in the cytoplasm, where most of the cycle’s reactions occur.
Q.15 – Blood urea decreases in all of the following conditions, except-
A) Liver cirrhosis
B) Pregnancy
C) Renal failure
D) Urea cycle disorders
Answer: C) Renal failure
Explanation: In renal failure, blood urea levels typically increase due to decreased kidney function and impaired urea excretion. In conditions like liver cirrhosis, pregnancy, and urea cycle disorders, blood urea levels can decrease due to reduced urea synthesis or dilution.
Q.16 – All of the following amino acids are donors of one carbon compounds except-
A) Histidine
B) Tyrosine
C) Tryptophan
D) Serine
Answer: B) Tyrosine
Explanation: Tyrosine is not a donor of one-carbon units. It is primarily involved in the synthesis of hormones and neurotransmitters. Serine, Histidine, and Tryptophan can donate one-carbon units in various metabolic pathways.
Q.17 – The two nitrogens of urea are derived from-
A) Aspartate and ammonia
B) Glutamate and ammonia
C) Arginosuccinate and ammonia
D) Alanine and ammonia
Answer: A) Aspartate and ammonia
Explanation: The urea cycle utilizes nitrogen from ammonia and aspartate. Ammonia provides one nitrogen directly, and aspartate contributes the second nitrogen through its conversion into fumarate and then urea.
Q.18 – Which of the following amino acids is not required for the synthesis of glutathione?
A) Serine
B) Cysteine
C) Glutamic acid
D) Glycine
Answer: A) Serine
Explanation: Glutathione synthesis requires cysteine, glutamic acid, and glycine. Serine is not involved in this process.
Q.19 – The first line of defense in the brain in conditions of hyperammonemia is-
A) Urea formation
B) Glutamine synthesis
C) Glutamate synthesis
D) Asparagine formation
Answer: B) Glutamine synthesis
Explanation: Glutamine synthesis is a critical mechanism for detoxifying ammonia in the brain. Ammonia is rapidly converted to glutamine by glutamine synthetase, helping to prevent neurotoxicity.
Q.20 – Which coenzyme is required for the oxidative deamination of most amino acids?
A) Folic acid
B) Pyridoxal-P
C) FMN
D) FAD
Answer: C) FMN
Explanation: FMN is essential for the oxidative deamination of amino acids, facilitating the removal of an amino group as part of the catabolism of amino acids.
Q.21 – Choose the incorrect statement about the amino acid glycine-
A) One carbon donor
B) Required for the synthesis of heme
C) Forms oxalates upon catabolism
D) Both glucogenic and ketogenic
Answer: D) Both glucogenic and ketogenic
Explanation: The statement that glycine is both glucogenic and ketogenic is incorrect. Glycine is primarily glucogenic, meaning it can be converted into glucose via gluconeogenesis, but it is not ketogenic; it does not lead to the production of ketone bodies.
Q.22 – Which of the following is required as a coenzyme for the transamination reactions?
A) Coenzyme A
B) Pyridoxal-P
C) Folic acid
D) Cobalamin
Answer: B) Pyridoxal-P
Explanation: Pyridoxal phosphate (vitamin B6) is a coenzyme that is essential for transamination reactions. These reactions involve the transfer of an amino group from an amino acid to a keto acid, forming new amino acids.
Q.23 – A patient diagnosed with Homocystinuria should be supplemented with all of the following vitamins except-
A) Vitamin C
B) Folic acid
C) Vitamin B12
D) Pyridoxal-P
Answer: A) Vitamin C
Explanation: Vitamin C is not directly involved in the metabolic pathways affected by Homocystinuria, which is characterized by elevated levels of homocysteine due to deficiencies in enzymes or cofactors like folic acid, vitamin B12, and pyridoxal phosphate (vitamin B6). These nutrients are essential for homocysteine metabolism.
Q.24 – In a patient suffering from Cystinuria, which of the following amino acids is not seen in the urine of affected patients?
A) Arginine
B) Methionine
C) Lysine
D) Ornithine
Answer: B) Methionine
Explanation: Cystinuria is a genetic disorder that leads to impaired transport of certain amino acids in the kidney, causing an excess excretion of cystine, ornithine, arginine, and lysine in the urine. Methionine is not typically excreted in increased amounts in this condition.
Q.25 – Positive nitrogen balance is seen in all of the following conditions except-
A) Pregnancy
B) Growth
C) Fever
D) Convalescence
Answer: C) Fever
Explanation: Positive nitrogen balance, where nitrogen intake exceeds nitrogen loss, is typically seen during periods of growth, pregnancy, and convalescence when the body is building tissues. In contrast, fever often leads to a negative nitrogen balance due to increased protein breakdown and loss.
Q.26 – The L-amino acids are absorbed from the intestine by which of the following?
A) Active transport
B) Passive diffusion
C) Pinocytosis
D) Facilitated diffusion
Answer: A) Active transport
Explanation: L-amino acids are primarily absorbed through active transport mechanisms in the intestine. This process uses energy to transport amino acids against their concentration gradient, ensuring efficient uptake into the body.
Q.27 – A child presented with increased frequency of urination, photophobia, and impairment of vision. Which of the following defects could be responsible for the said symptoms?
A) Tyrosinosis
B) Cystinosis
C) Alkaptonuria
D) Albinism
Answer: B) Cystinosis
Explanation: Cystinosis is a metabolic disorder where cystine accumulates in the body’s cells and tissues, leading to kidney problems (increased urination). It can also affect the eyes, causing photophobia and vision issues. The other listed conditions do not typically present with these symptoms.
Q.28 – Which of the following statements about Glutamate dehydrogenase is correct?
A) Required for transamination reactions
B) Universally present in all the cells of the body
C) Can utilize either NAD+ or NADP+
D) Catalyzes conversion of glutamate to glutamine
Answer: C) Can utilize either NAD+ or NADP+
Explanation: Glutamate dehydrogenase can utilize either NAD+ or NADP+ as coenzymes in its reaction, which involves the reversible oxidative deamination of glutamate into α-ketoglutarate and ammonia. This enzyme does not catalyze the conversion of glutamate to glutamine; that reaction is carried out by glutamine synthetase.
Q.29 – A child was brought to the pediatric OPD with a complaint of the passage of black-colored urine. A disorder of Phenylalanine metabolism was diagnosed. A low phenylalanine diet and supplementation of vitamin C were recommended. Which enzyme defect is expected in this child?
A) Phenylalanine hydroxylase
B) Tyrosine transaminase
C) Homogentisic acid oxidase
D) Hydrolase
Answer: C) Homogentisic acid oxidase
Explanation: This child likely has Alkaptonuria, a disorder characterized by the accumulation and excretion of homogentisic acid, leading to the darkening of urine upon exposure to air. The defect is in the enzyme homogentisic acid oxidase, part of the pathway that breaks down phenylalanine and tyrosine.
Q.30 – Dopamine is synthesized from which of the following amino acids?
A) Tyrosine
B) Tryptophan
C) Histidine
D) Methionine
Answer: A) Tyrosine
Explanation: Dopamine is synthesized from tyrosine, an amino acid that is hydroxylated to form L-DOPA, which is then decarboxylated to produce dopamine. This pathway is crucial for the production of an important neurotransmitter involved in brain function and mood regulation.
Q.31 – In mammalian tissue, serine can be a biosynthetic precursor for which amino acid?
A) Methionine
B) Glycine
C) Arginine
D) Lysine
Answer: B) Glycine
Explanation: In mammalian tissues, serine can be directly converted to glycine through a simple enzyme-catalyzed reaction involving serine hydroxymethyltransferase. This reaction is important for the production of glycine, a versatile amino acid used in various metabolic processes.
Q.32 – Hydroxylation of Phenylalanine to Tyrosine requires all except
A) Glutathione
B) Tetrahydrobiopterin
C) Molecular oxygen
D) NADPH
Answer: A) Glutathione
Explanation: The conversion of phenylalanine to tyrosine is catalyzed by the enzyme phenylalanine hydroxylase, which requires tetrahydrobiopterin, molecular oxygen, and NADPH as cofactors. Glutathione is not involved in this particular biochemical reaction.
Q.33 – The amino acid that undergoes oxidative deamination at the highest rate is-
A) Glutamine
B) Glutamate
C) Aspartate
D) Alanine
Answer: B) Glutamate
Explanation: Glutamate undergoes oxidative deamination at a high rate, catalyzed by the enzyme glutamate dehydrogenase. This reaction plays a critical role in ammonia detoxification and in the metabolic pathways linking amino acid catabolism to the Krebs cycle.
Q.34 – All of the following statements regarding serotonin are true except-
A) Causes vasodilation
B) Causes bronchoconstriction
C) Metabolized to 5-hydroxyindole acetic acid
D) Causes diarrhea
Answer: A) Causes vasodilation
Explanation: Serotonin typically causes vasoconstriction rather than vasodilation. It is also involved in bronchoconstriction, is metabolized to 5-hydroxyindole acetic acid, and can cause diarrhea due to its effects on the gastrointestinal tract.
Q.35 – Choose the incorrect statement about cysteine-
A) Carbon skeleton is provided by serine
B) Sulfur group is provided by methionine
C) Forms hippuric acid for detoxification of xenobiotics
D) Required for bile salt formation
Answer: C) Forms hippuric acid for detoxification of xenobiotics
Explanation: Cysteine does not form hippuric acid; rather, hippuric acid is formed from benzoic acid and glycine. Cysteine’s carbon skeleton is indeed derived from serine, and its sulfur comes from methionine. It is also important for the synthesis of bile salts.
