Amino Acid Metabolism

Question 1

What are the sources of amino acids?

Answer 1

• Degradation of ingested protein
• Degradation of synthesized endogenous protein
• AA biosynthesis

Question 2

What are the free amino acids used for?

Answer 2

• Make purines/pyrimidines
• Make glucose
• Make ketones
• Degraded into nitrogen for release as urea

Question 3

What enzymes are the most rapidly degraded?

Answer 3

Proteins most rapidly degraded are often ones

of the rate limiting step

Question 4

What is nitrogen balance?

Answer 4

It is the intake and excretion of nitrogen and should be 0 in normal people.

Question 5

When does positive nitrogen balance occur?

Answer 5

Pregnancy
Growth
Bodybuilding

Question 6

When does negative nitrogen balance occur?

Answer 6

Starvation
Cancer
Trauma

Question 7

What is the general pathway for urea formation from amino acid degradation?

Answer 7

Free amines -> Glutamate -> Ammonia OR Aspartate -> Urea

Question 8

Where is urea synthesized?

Answer 8

Liver

Question 9

What is the transamination reaction?

Answer 9

It is the transfer of the amine group on an amino acid to α-ketoglutarate which then generates glutamate

Question 10

What is the cofactor necessary for the transaminase enzymes to carry out transamination?

Answer 10

Pyridoxal Phosphate

Question 11

What serves as the nitrogen reservoir in the body?

Answer 11

Glutamate

Question 12

What do elevated levels of Alanine transaminase and/or Aspartate transaminase indicate?

Answer 12

They indicate liver tissue damage as the hepatocytes are lysing.

Question 13

How is glutamate converted to aspartate?

Answer 13

Aspartate Transaminase

Question 14

How is glutamate converted to ammonia?

Answer 14

Glutamate Dehydrogenase

Question 15

What is the primary regulated step of urea synthesis?

Answer 15

Formation of carbamoyl phosphate

Question 16

What is the enzyme that catalyzes the regulated step of urea synthesis?

Answer 16

Carbamoyl phosphate synthetase I

Question 17

What is the allosteric activator of carbamoyl phosphate synthetase I?

Answer 17

N-acetylglutamate

Question 18

What enzyme converts arginine into urea?

Answer 18

Arginase

Question 19

Within the cell, where does the conversion of NH3 to carbomoyl phosphate and conversion to citrulline occur?

Answer 19

In the mitochondria. The rest of the urea cycle reactions occur in the cytosol.

Question 20

What can occur with hyperammonemia?

Answer 20

Hepatic coma

Question 21

What are glucogenic amino acids?

Answer 21

They can be converted to TCA cycle intermediates

or pyruvate for gluconeogensis

Question 22

What are ketogenic amino acids?

Answer 22

They can be converted to acetyl CoA, acetoacetyl CoA, or acetoacetate

Question 23

Name the ketogenic amino acids.

Answer 23

Lysine

Leucine

Question 24

What occurs to amino acid and protein synthesis after a meal?

Answer 24

Protein synthesis will increase under the effect of insulin

Question 25

What occurs to protein synthesis during an overnight fast?

Answer 25

Protein synthesis will be inhibited, with glucagon promoting protein degradation