Amino Acids Metabolism_2024

Which enzyme catalyzes the rate-limiting step of the urea cycle?

• A. Argininosuccinase

• B. Ornithine Transcarbamylase

• C. Carbamoyl Phosphate Synthetase

• D. Arginase

Answer: C. Carbamoyl Phosphate Synthetase

What is the fate of ammonia in peripheral tissues?

• A. Conversion to urea

• B. Formation of glutamine

• C. Binding to α-ketoglutarate

• D. Direct excretion

Answer: B. Formation of glutamine

then to liver to be converted into urea

Which coenzyme is required for aminotransferase activity?

• A. Biotin

• B. Pyridoxal phosphate

• C. Folic acid

• D. NADPH

Answer: B. Pyridoxal phosphate

Which amino acid is exclusively ketogenic?

• A. Alanine

• B. Leucine

• C. Phenylalanine

• D. Tyrosine

Answer: B. Leucine

What is the primary function of transamination?

• A. Ammonia excretion

• B. Protein synthesis

• C. Transfer of amino groups to α-ketoglutarate

• D. Glutamine production

Answer: C. Transfer of amino groups to α-ketoglutarate

What is the significance of elevated AST and ALT levels?

• A. Enhanced protein synthesis

• B. Increased ammonia production

• C. Liver or muscle damage

• D. Active urea synthesis

Answer: C. Liver or muscle damage

Which intermediate links the urea cycle and the Krebs cycle?

• A. Fumarate

• B. Pyruvate

• C. Citrulline

• D. Acetyl-CoA

Answer: A. Fumarate

Which amino acid is a major nitrogen donor in transamination?

• A. Alanine

• B. Glutamate

• C. Aspartate

• D. Tyrosine

Answer: B. Glutamate

Which molecule provides the first nitrogen in the urea cycle?

• A. Aspartate

• B. Glutamine

• C. Ammonia

• D. Ornithine

Answer: C. Ammonia

What distinguishes glucogenic from ketogenic amino acids?

• A. Their participation in transamination

• B. Their end products during catabolism

• C. Their role in protein synthesis

• D. Their ability to form ammonia

Answer: B. Their end products during catabolism

Glutamate is the only amino acid that undergoes rapid oxidative deamination.

Answer: True

Transamination occurs only in the liver.

• Answer: False
  Explanation: Transamination occurs in multiple tissues, including muscle and kidney.

Hyperammonemia is harmless under normal physiological conditions.

Answer: False
Explanation: Elevated ammonia levels are toxic to the CNS.

Urea synthesis occurs exclusively in the cytosol.

• Answer: False
  Explanation: The urea cycle involves both mitochondrial and cytosolic enzymes.

Ketogenic amino acids can be converted into glucose.

Answer: False
Explanation: Ketogenic amino acids are converted into ketone bodies, not glucose.

ALT and AST are involved in the urea cycle.

Answer: False
Explanation: ALT and AST catalyze transamination reactions, not the urea cycle.

Alanine serves as a nitrogen transporter from muscle to the liver.

Answer: True

Pyridoxal phosphate is derived from Vitamin B6.

Answer: True

The urea cycle requires energy in the form of ATP.

Answer: True

Fumarate produced in the urea cycle is a substrate for gluconeogenesis.

Answer: True

What is the primary nitrogen source for the urea cycle?

Answer: Ammonia and aspartate.

Name two amino acids that are both glucogenic and ketogenic.

Answer: Phenylalanine and Tyrosine.

What is the role of glutamine synthetase in ammonia transport?

• Answer: Converts glutamate and ammonia into glutamine for safe transport to the liver.

Which enzyme is responsible for oxidative deamination in amino acid catabolism?

Answer: Glutamate dehydrogenase.

How does the urea cycle connect to the Krebs cycle?

Answer: Through fumarate, which enters the Krebs cycle for further metabolism.