Amino Acid Metabolism

Question 1

Assertion: Glutamine is the major carrier of ammonia from peripheral tissues. Reason: Glutamine synthetase converts ammonia into glutamine.

Answer 1

A

Question 2

Assertion: Ammonia is toxic to cells. Reason: It interferes with α-ketoglutarate formation by reversing the glutamate dehydrogenase reaction.

Answer 2

A

Question 3

Assertion: In peripheral tissues, excess ammonia is converted into glutamine. Reason: This detoxification protects tissues from ammonia toxicity.

Answer 3

A

Question 4

Assertion: Alanine serves as an ammonia transporter from muscle to liver. Reason: The alanine-glucose cycle transfers nitrogen and carbon skeletons to the liver.

Answer 4

A

Question 5

Assertion: Transamination reactions help assimilate ammonia. Reason: They funnel amino nitrogen from many amino acids into key intermediates.

Answer 5

A

Question 6

Assertion: Glutamate dehydrogenase regulates ammonia levels. Reason: It catalyzes the reversible conversion between glutamate and α-ketoglutarate with ammonia release.

Answer 6

A

Question 7

Assertion: The urea cycle occurs in the liver. Reason: Its enzymes are divided between the mitochondria and cytosol of hepatocytes.

Answer 7

A

Question 8

Assertion: Carbamoyl phosphate synthetase I initiates the urea cycle. Reason: It requires N‑acetylglutamate (NAG) as an allosteric activator.

Answer 8

A

Question 9

Assertion: Blood ammonia levels are a sensitive indicator of liver function. Reason: Impaired urea synthesis leads to ammonia accumulation in the blood.

Answer 9

A

Question 10

Assertion: Hepatic glutaminase converts glutamine to glutamate. Reason: This reaction releases ammonia for urea synthesis in the liver.

Answer 10

A

Question 11

Assertion: Transaminases require pyridoxal phosphate (PLP) as a coenzyme. Reason: Vitamin B6 is essential for transamination reactions.

Answer 11

A

Question 12

Assertion: Converting ammonia to urea prevents toxic ammonia buildup. Reason: Urea is non-toxic and is excreted via the kidneys.

Answer 12

A

Question 13

Assertion: In skeletal muscle, ammonia is converted to alanine. Reason: The resulting alanine is transported to the liver for gluconeogenesis and urea production.

Answer 13

A

Question 14

Assertion: Glutamine is shuttled to the liver in the blood. Reason: Hepatic glutaminase breaks down glutamine to provide ammonia for the urea cycle.

Answer 14

A

Question 15

Assertion: The alanine-glucose cycle links muscle and liver metabolism. Reason: It transfers both carbon and nitrogen between these tissues.

Answer 15

A

Question 16

Assertion: Urea synthesis consumes ATP. Reason: ATP is required to form carbamoyl phosphate from ammonia for the urea cycle.

Answer 16

A

Question 17

Assertion: Urea cycle enzyme activity increases with high protein intake. Reason: Elevated amino acids lead to increased ammonia, stimulating urea synthesis.

Answer 17

A

Question 18

Assertion: Excess ammonia causes encephalopathy. Reason: Elevated ammonia disrupts neurotransmitter synthesis and energy metabolism in the brain.

Answer 18

A

Question 19

Assertion: Ammonia accumulation can alter acid-base balance. Reason: High ammonia levels shift the equilibrium to form ammonium ions, affecting pH.

Answer 19

A

Question 20

Assertion: Hormonal signals regulate urea cycle enzyme expression. Reason: Glucagon upregulates and insulin downregulates these enzymes in the liver.

Answer 20

A

Question 21

Assertion: N-acetylglutamate (NAG) is essential for urea cycle activity. Reason: It is an allosteric activator of carbamoyl phosphate synthetase I.

Answer 21

A

Question 22

Assertion: The urea cycle spans both the mitochondria and cytosol. Reason: Some enzymes are mitochondrial while others operate in the cytosol for efficient flux.

Answer 22

A

Question 23

Assertion: Urea is eliminated by the kidneys. Reason: Urea is water-soluble and is filtered by the glomeruli.

Answer 23

A

Question 24

Assertion: Defects in urea cycle enzymes lead to hyperammonemia. Reason: Inherited enzyme deficiencies impair ammonia detoxification.

Answer 24

A

Question 25

Assertion: The glucose-alanine cycle aids in nitrogen disposal from muscle. Reason: Alanine produced in muscle is used by the liver to generate glucose and urea.

Answer 25

A

Question 26

Assertion: Glutamate dehydrogenase plays a dual role in ammonia detoxification and energy metabolism. Reason: It catalyzes the reversible conversion of glutamate to α‑ketoglutarate with ammonia release.

Answer 26

A

Question 27

Assertion: The urea cycle is compartmentalized between the mitochondria and cytosol. Reason: Spatial separation of enzymes ensures a unidirectional flow of intermediates.

Answer 27

A

Question 28

Assertion: N-acetylglutamate synthesis increases with protein intake. Reason: Elevated levels of glutamate and acetyl-CoA stimulate N-acetylglutamate synthase.

Answer 28

A

Question 29

Assertion: The liver’s dual localization of glutaminase and glutamine synthetase is crucial for ammonia regulation. Reason: This compartmentalization allows the liver to both remove and generate ammonia.

Answer 29

A

Question 30

Assertion: Transamination reactions contribute to urea production. Reason: They redistribute amino groups to glutamate, which can be oxidatively deaminated to yield ammonia.

Answer 30

A

Question 31

Assertion: Renal ammoniagenesis is upregulated during metabolic acidosis. Reason: Increased glutamine delivery to the kidney enhances the production of ammonium, aiding acid excretion.

Answer 31

A

Question 32

Assertion: The reversal of the glutamate dehydrogenase reaction depletes TCA cycle intermediates under hyperammonemic conditions. Reason: Excess ammonia pushes the reaction backward, reducing α‑ketoglutarate levels.

Answer 32

A

Question 33

Assertion: The alanine-glucose cycle imposes an energetic cost on the liver. Reason: Gluconeogenesis from alanine requires ATP, diverting energy from other processes.

Answer 33

A

Question 34

Assertion: Blood ammonia is a sensitive indicator of liver failure. Reason: Impaired urea cycle function leads to ammonia accumulation in the blood.

Answer 34

A

Question 35

Assertion: Hormonal regulation influences urea cycle enzyme expression. Reason: Glucagon upregulates while insulin downregulates these enzymes in hepatocytes.

Answer 35

A

Question 36

Assertion: Carbamoyl phosphate synthetase I activity is dependent on N-acetylglutamate. Reason: N-acetylglutamate acts as an essential allosteric activator for CPSI.

Answer 36

A

Question 37

Assertion: The production of fumarate in the urea cycle connects nitrogen metabolism to the TCA cycle. Reason: Fumarate can be converted into oxaloacetate, supporting gluconeogenesis or energy production.

Answer 37

A

Question 38

Assertion: Inherited defects in urea cycle enzymes result in hyperammonemia. Reason: Enzyme deficiencies impede ammonia detoxification, causing its accumulation.

Answer 38

A

Question 39

Assertion: Astrocytic glutamine synthetase protects neurons from ammonia toxicity. Reason: It converts excess ammonia and glutamate into glutamine, reducing neurotoxic levels.

Answer 39

A

Question 40

Assertion: Alternative nitrogen excretion pathways are activated when the urea cycle is impaired. Reason: Nitrogen scavengers conjugate with amino acids to form excretable compounds.

Answer 40

A

Question 41

Assertion: Inherited urea cycle disorders lead to episodic encephalopathy. Reason: Fluctuating protein intake can precipitate acute ammonia surges that impair brain function.

Answer 41

A

Question 42

Assertion: The transcriptional regulation of urea cycle enzymes is influenced by glucocorticoids. Reason: Glucocorticoids upregulate expression of key urea cycle genes during stress.

Answer 42

A

Question 43

Assertion: Dietary administration of α-keto acid analogues can help manage urea cycle disorders. Reason: They reduce nitrogen intake while supplying essential nutrients.

Answer 43

A

Question 44

Assertion: Hyperammonemia in urea cycle disorders can lead to cerebral edema. Reason: Excess ammonia crosses the blood-brain barrier, disrupting osmotic balance and brain metabolism.

Answer 44

A

Question 45

Assertion: In urea cycle defects, carbamoyl phosphate accumulation may shunt into pyrimidine biosynthesis. Reason: Excess carbamoyl phosphate serves as a substrate in the orotic acid pathway, causing orotic aciduria.

Answer 45

A

Question 46

Assertion: The compartmentalization of urea cycle enzymes is critical for metabolic flux. Reason: Spatial separation between mitochondria and cytosol prevents futile cycles and directs metabolite flow.

Answer 46

A

Question 47

Assertion: Deficiency of N-acetylglutamate synthase (NAGS) produces a urea cycle defect phenotype. Reason: Without NAG, carbamoyl phosphate synthetase I cannot be activated, impairing urea synthesis.

Answer 47

A

Question 48

Assertion: The reversible reaction catalyzed by glutamate dehydrogenase is allosterically regulated by both NADH and ADP. Reason: This dual regulation enables the enzyme to respond to the cellular energy status and redox balance.

Answer 48

A

Question 49

Assertion: Persistent hyperammonemia leads to inhibition of neurotransmitter synthesis. Reason: Excess ammonia impairs production of key neurotransmitters like glutamate and GABA in the brain.

Answer 49

A

Question 50

Assertion: Alternative nitrogen excretion via nitrogen scavengers can bypass a defective urea cycle. Reason: These agents conjugate with amino acids to form compounds that are excreted in the urine.

Answer 50

A

Question 51

Assertion: Inherited urea cycle disorders often present with episodic encephalopathy due to variable protein intake. Reason: Metabolic stress from fluctuations in dietary protein precipitates acute ammonia surges.

Answer 51

A

Question 52

Assertion: Astrocytic glutamine synthetase is crucial for cerebral ammonia detoxification. Reason: Its deficiency leads to ammonia accumulation in the brain, exacerbating neurotoxicity.

Answer 52

A

Question 53

Assertion: Elevated blood urea nitrogen (BUN) levels can result from impaired renal clearance rather than increased urea synthesis. Reason: Renal dysfunction decreases urea excretion despite normal hepatic activity.

Answer 53

A

Question 54

Assertion: Carglumic acid is effective in treating NAGS deficiency. Reason: It mimics N-acetylglutamate, thereby restoring carbamoyl phosphate synthetase I activity and urea cycle function.

Answer 54

A

Question 55

Assertion: The interplay between the urea cycle and the TCA cycle exemplifies metabolic integration. Reason: Fumarate produced during urea synthesis replenishes TCA cycle intermediates, linking nitrogen and energy metabolism.

Answer 55

A

Question 56

Assertion: Inherited urea cycle disorders require lifelong dietary management. Reason: Chronic enzyme deficiencies necessitate strict protein control and pharmacological intervention to prevent hyperammonemia.

Answer 56

A