Nitrogen Metabolism and Fates of AAs

Question 1

name the essential amino acids

Answer 1

• phenylalalinee
• valin
• tryptophan
• threonine
• isoleucine
• methionine
• histidine
• argigine (conditionally essential)
• leucine
• lysine

Question 2

name the amino acids whose side chains are related to glycolysis or TCA intermediates

Answer 2

• pyruvate = alanine
• oxaloacetate = aspartate, asparagine
• alpha-KG = glutamine

Question 3

describe protein degradation pathways

Answer 3

Question 4

describe the role of the liver in nitrogen metabolism

Answer 4

• liver is the site where most of the amino acids release their amino groups as ammonia
  
  • NH3 is toxic
  • carbon skeleton is released
• NH3 is detoxified to urea via the urea cycle in liver
• urea is the major end-product of N metabolism
• amino acid carbon skeletons are:
  
  • used for gluconeogenesis
  • burned in the TCA cycle

Question 5

describe the role of kidney in nitrogen metabolism

Answer 5

• urea formed in the liver is transported to the kidneys where it is excreted in the urine
• kidneys also excrete ammonia as ammonium ions
  
  • regulation of acid base balance
  • ammonia source is from glutamine (glutaminase enzyme)

Question 6

_____ is the major nitrogen compound excreted in the urine

Answer 6

urea is the major nitrogen compound excreted in the urine

Question 8

what are the 3 or 4 D’s of pellagra

Answer 8

• Diarrhea
• Dermatitis
• Dementia
• (Death)

Question 9

describe cystinuria

Answer 9

• tubular reabsorption of cystine is decreased (along with dibasic AA ornithine, arginine, lysine) due to an inheretied deficiency of the cystine transporter
• cystine is excreted in urine
• cysteine tends to precipitate in the renal tubules (renal stones) in the renal tract

Question 10

contrast the crystals seen in cystinuria with crystals seen in gout

Answer 10

• cystinuria: hexagonal cysteine crystal
• gout: birefringement crystals of sodium urate

Question 11

describe Hartnup disease

Answer 11

• inherited defect in the transport of tryptophan
  
  • a neutral AA
• decreased dietary absorption of tryptophan and increased excretion of tryptophan
• manifestations of tryptophan deficiency
  
  • may lead to NAD+ deficiency (pellagra)

Question 12

describe why pellagra occurs in Hartnup disease

Answer 12

Question 13

contrast glucogenic vs ketogenic amino acids

Answer 13

• glucogenic: catabolism yields pyruvate or one of the intermediates of the citric acid cycle
  
  • substrates for gluconeogesis
• ketogenic: yields acetoacetate, acetyl CoA or acetoacetyl CoA
  
  • not substrates for gluconeogenesis

Question 14

which 2 amino acids are used in ketone body synthesis?

Answer 14

Lysine and leucine

Question 15

describe alanine metabolism

Answer 15

• alanine is the major transport form of amino acid from the muscle (important during starvation)
• alanine (pyruvate) is the major precursor of gluconeogenesis during starvation
• glucose-alanine cycle involves the muscle (where alanine is formed) and liver (site of gluconeogenesis)

Question 16

describe the glucose-alanine cycle

Answer 16

• pyruvate formed in the muscle by glycolysis is transaminated to alanine
• alanine is transported to the liver and is coverted to glucose by gluconeogenesis

Question 17

describe glutamate metabolism

Answer 17

Question 18

describe aspartate metabolism

Answer 18