Amino Acid Metabolism Practice Questions

Q: VMA is excreted in urine in which condition -

Pheochromocytoma. ***Pheochromocytoma*** - Pheochromocytoma is characterized by excessive secretion of catecholamines, leading to increased levels of **vanillylmandelic acid (VMA)** in the urine. - It is often associated with symptoms like **hypertension**, palpitations, and sweating due to catecholamine release. *Alkaptonuria* - Caused by a deficiency in **homogentisate oxidase**, leading to the accumulation of **homogentisic acid**, not VMA. - Clinically presents with **dark urine** and can lead to **ochronosis**, but does not involve catecholamines. *Phenylketonuria* - A metabolic disorder resulting from a deficiency in **phenylalanine hydroxylase**, leading to elevated levels of **phenylalanine** rather than VMA. - Symptoms include intellectual disability and musty odor, unrelated to catecholamine metabolism. *Diabetic ketoacidosis* - This is a condition caused by severe **insulin deficiency**, resulting in elevated ketone bodies and glucose levels, but does not cause increased VMA excretion. - Symptoms include **fruity breath**, dehydration, and metabolic acidosis, focusing on ketone production rather than catecholamine metabolism.

Q: In which condition is 5-Hydroxyindoleacetic acid (HIAA) elevated in urine?

Carcinoid. ***Carcinoid*** - **Carcinoid tumors** can synthesize and release large amounts of **serotonin**, which is metabolized in the body to **5-HIAA**. - Elevated **urinary 5-HIAA** is a key diagnostic marker for **carcinoid syndrome**, indicating excessive serotonin production. *Alkaptonuria* - This is a rare genetic disorder characterized by the accumulation of **homogentisic acid** in the body, leading to dark urine upon standing and ultimately **ochronosis**. - It does not involve abnormalities in serotonin metabolism or 5-HIAA levels. *Albinism* - Albinism is a group of inherited disorders characterized by very **little or no melanin pigment production**, commonly affecting the skin, hair, and eyes. - This condition is related to **tyrosine metabolism** and has no direct link to 5-HIAA levels. *Phenylketonuria* - **PKU** is a metabolic disorder caused by a deficiency in the enzyme **phenylalanine hydroxylase**, leading to a buildup of **phenylalanine** in the body. - This condition primarily affects phenylalanine metabolism and has no direct relationship with 5-HIAA levels, which are associated with serotonin metabolism.

Q: Which of the following compounds is not formed with the involvement of glycine?

Thyroxine. ***Thyroxine*** - **Thyroxine** (and other thyroid hormones) are derived from the amino acid **tyrosine**. - Their synthesis involves iodination and coupling reactions of tyrosine residues within the protein **thyroglobulin**. *Heme* - **Glycine** is a direct precursor for the initial step in **heme synthesis**. - It condenses with **succinyl CoA** to form α-amino-β-ketoadipate, which then decarboxylates to form δ-aminolevulinate (ALA). *Purines* - **Glycine** contributes part of its structure to the **purine ring**. - Specifically, the **nitrogen at position 7** and the **carbons at positions 4 and 5** of the purine ring are derived from glycine. *Glutathione* - **Glutathione** is a tripeptide composed of three amino acids: **glutamate**, **cysteine**, and **glycine**. - **Glycine** is the C-terminal amino acid of glutathione and is essential for its structure and function as an antioxidant.

Q: Creatinine is formed from -

Creatine. ***Creatine*** - **Creatinine** is a waste product formed from the non-enzymatic, irreversible degradation of **creatine** and **creatine phosphate**, primarily in muscles. - **Creatine** itself is synthesized endogenously from three amino acids: **glycine, arginine, and methionine** (as S-adenosylmethionine) through a two-step enzymatic process in the kidney and liver. - The amount of creatinine produced daily is relatively constant and directly proportional to an individual's **muscle mass**, making it a useful marker for renal function. *Lysine* - **Lysine** is an **essential amino acid** and a precursor for various compounds like **carnitine** but is not involved in creatinine or creatine formation. - Deficiency can lead to impaired protein synthesis but does not impact creatinine levels. *Leucine* - **Leucine** is another **essential amino acid** and a **branched-chain amino acid (BCAA)** crucial for muscle protein synthesis and repair. - It does not serve as a direct precursor for creatinine or creatine. *Histidine* - **Histidine** is an **essential amino acid** and a precursor for **histamine** and other important compounds, but not creatinine or creatine. - It plays roles in immune response and gastric acid secretion.

Q: Which of the following is classified as an essential amino acid?

Lysine. ***Lysine*** - **Essential amino acids** cannot be synthesized by the human body and must be obtained through the diet. - Lysine is one of the **nine essential amino acids** necessary for **protein synthesis**, collagen formation, calcium absorption, and other metabolic functions. - Remembered by the mnemonic: **PVT TIM HALL** (Phe, Val, Thr, Trp, Ile, Met, His, Arg*, Leu, Lys). *Aspartic acid* - Aspartic acid is a **non-essential amino acid**, meaning the body can synthesize it from oxaloacetate through transamination. - It plays a role in the **urea cycle** and **gluconeogenesis**. - Functions as an excitatory neurotransmitter in the central nervous system. *Glutamic acid* - Glutamic acid is also a **non-essential amino acid** that the body can readily produce from α-ketoglutarate. - It is a crucial excitatory **neurotransmitter** and a precursor for other amino acids like **glutamine** and **proline**. - Important in nitrogen metabolism and the urea cycle. *None of the options* - This option is incorrect because **lysine** is clearly an essential amino acid that must be obtained from dietary sources.

Q: Which of the following is required in the synthesis of acetylcholine -

Choline. ***Choline*** - **Choline** is a **precursor** to acetylcholine, providing the **choline moiety** for its synthesis. - The enzyme **choline acetyltransferase** combines choline with acetyl-CoA (which provides the acetyl group) to form acetylcholine. *Inositol* - **Inositol** is a sugar alcohol that plays a role in **cell signaling** and as a secondary messenger in various pathways. - It is not directly involved as a substrate in the synthesis of acetylcholine. *Carnitine* - **Carnitine** is essential for the **transport of fatty acids** into the mitochondria for beta-oxidation. - It does not participate in the enzymatic reactions that produce acetylcholine. *Glycine* - **Glycine** is an amino acid that functions as an **inhibitory neurotransmitter** in the central nervous system. - While it is a neurotransmitter, it is not a component or precursor for acetylcholine synthesis.

Q: Which coenzyme is not required in the formation of glutamate?

Thiamine pyrophosphate. ***Thiamine pyrophosphate*** - **Thiamine pyrophosphate (TPP)** is a coenzyme derived from **vitamin B1** that is essential for reactions involving decarboxylation, such as those catalyzed by pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase. - The formation of glutamate primarily involves transamination or reductive amination, which do not require TPP. *Pyridoxal phosphate* - **Pyridoxal phosphate (PLP)**, derived from **vitamin B6**, is a crucial coenzyme for **transamination reactions**, which are a major pathway for glutamate synthesis (e.g., from alpha-ketoglutarate). - It also plays a role in decarboxylation and deamination reactions of amino acids. *Niacin* - **Niacin (vitamin B3)** is a precursor for **NAD+** and **NADP+**, which are essential coenzymes in many metabolic pathways. - **NADPH**, derived from NADP+, is required as a reductant in the **reductive amination** of **alpha-ketoglutarate** to form glutamate, catalyzed by glutamate dehydrogenase. *None of the above* - This option is incorrect because **thiamine pyrophosphate** is indeed not required for the formation of glutamate. - The other two coenzymes, **pyridoxal phosphate** and **niacin (as NAD(P)H)**, are involved in glutamate synthesis.

Q: Fumarate is formed from which amino acid?

Tyrosine. ***Tyrosine*** - **Tyrosine** is a **glucogenic and ketogenic amino acid** that is catabolized to acetoacetate and fumarate. - **Fumarate** then enters the **citric acid cycle (Krebs cycle)**, whereas acetoacetate is a ketone body. *Methionine* - **Methionine** is an **essential amino acid** and a precursor for **S-adenosylmethionine (SAM)**, a methyl donor in many reactions. - Its catabolism produces **succinyl CoA**, not fumarate, through a series of steps via propionyl CoA. *Valine* - **Valine** is a **branched-chain amino acid (BCAA)** that is exclusively **glucogenic**. - Its catabolism ultimately leads to the formation of **succinyl CoA**, which can enter the citric acid cycle. *Histidine* - **Histidine** is an **essential amino acid** that is catabolized to **formiminoglutamate (FIGLU)**. - FIGLU is then converted to **glutamate**, which can eventually be deaminated to α-ketoglutarate, a citric acid cycle intermediate, but not directly fumarate.

Q: Boiled cabbage or rancid butter smelling urine is seen in

Isovaleric Acidaemia. ***Isovaleric Acidaemia*** - **Boiled cabbage or rancid butter odor** in urine is a classic feature of isovaleric acidemia, caused by the accumulation of isovaleric acid. - This **inborn error of metabolism** affects **leucine metabolism** due to deficiency of isovaleryl-CoA dehydrogenase. *Tyrosinemia* - Does NOT present with boiled cabbage or rancid butter odor. The characteristic features are **liver dysfunction** and **renal tubular defects**. - Tyrosinemia Type I is caused by deficiency of **fumarylacetoacetate hydrolase**, leading to accumulation of tyrosine metabolites. *Phenylketonuria* - Characterized by a **mousy or musty odor** in urine, resulting from the accumulation of phenylacetic acid. - The defect is in the enzyme **phenylalanine hydroxylase**, not associated with boiled cabbage odor. *Multiple carboxylase deficiency* - Typically presents with a **"cat urine" smell** due to the accumulation of various organic acids. - The deficiency impairs the function of several **biotin-dependent carboxylases**, not specifically linked to the boiled cabbage odor.

Q: Which amino acid is not involved in transamination?

Lysine. ***Lysine*** - **Lysine** cannot undergo transamination because it lacks the structural requirements for typical transaminase enzymes. - While lysine has both an **α-amino group** and an **ε-amino group**, its metabolic pathway involves **oxidative deamination** rather than transamination. - Along with **threonine**, lysine is one of only two amino acids that do not participate in transamination reactions. *Alanine* - **Alanine** is a major substrate for transamination, readily converting to pyruvate via **alanine transaminase (ALT)**. - This reaction involves the transfer of its **α-amino group** to an α-keto acid, typically α-ketoglutarate, forming glutamate. *Aspartate* - **Aspartate** is actively involved in transamination, converting to oxaloacetate via **aspartate transaminase (AST)**. - Its **α-amino group** is easily transferred to α-ketoglutarate, forming glutamate. *Histidine* - **Histidine** can undergo transamination, though less commonly cited as a primary substrate compared to aspartate and alanine. - It can transfer its **α-amino group** to an α-keto acid, leading to the formation of imidazolepyruvate.

Question 1

VMA is excreted in urine in which condition -

Accepted Answer

Pheochromocytoma

Answer

Alkaptonuria

Answer

Phenylketonuria

Answer

Diabetic ketoacidosis

Question 2

In which condition is 5-Hydroxyindoleacetic acid (HIAA) elevated in urine?

Accepted Answer

Carcinoid

Answer

Alkaptonuria

Answer

Albinism

Answer

Phenylketonuria

Question 3

Which of the following compounds is not formed with the involvement of glycine?

Accepted Answer

Thyroxine

Answer

Purines

Answer

Glutathione

Answer

Heme

Question 4

Creatinine is formed from -

Accepted Answer

Creatine

Answer

Lysine

Answer

Leucine

Answer

Histidine

Question 5

Which of the following is classified as an essential amino acid?

Accepted Answer

Lysine

Answer

Aspartic acid

Answer

Glutamic acid

Answer

None of the options

Question 6

Which of the following is required in the synthesis of acetylcholine -

Accepted Answer

Choline

Answer

Inositol

Answer

Carnitine

Answer

Glycine

Question 7

Which coenzyme is not required in the formation of glutamate?

Accepted Answer

Thiamine pyrophosphate

Answer

None of the above

Answer

Pyridoxal phosphate

Answer

Niacin

Question 8

Fumarate is formed from which amino acid?

Accepted Answer

Tyrosine

Answer

Methionine

Answer

Valine

Answer

Histidine

Question 9

Boiled cabbage or rancid butter smelling urine is seen in

Accepted Answer

Isovaleric Acidaemia

Answer

Tyrosinemia

Answer

Phenylketonuria

Answer

Multiple carboxylase deficiency

Question 10

Which amino acid is not involved in transamination?

Accepted Answer

Lysine

Answer

Alanine

Answer

Aspartate

Answer

Histidine

Amino Acid Metabolism — MCQs

Amino Acid Metabolism — MCQs

On this page

Practice by Chapter

Want unlimited practice?