Deck 20: Amino Acid Metabolism

Question 1

What reaction does glutamate dehydrogenase (GDH) catalyze?

A) The oxidative deamination of glutamate to yield α-ketoglutarate.
B) Phosphorylation of carbamate to yield carbamoyl phosphate.
C) The amidation of the γ carboxyl group of glutamate to form glutamine.
D) The deadenylation of glutamine synthetase (GS).
E) The adenylation of glutamine synthetase.

Answer 1

The oxidative deamination of glutamate to yield α-ketoglutarate.

Question 2

The carbon chains of amino acids enter the major metabolic pathways through all of these compounds, except:

A) α-ketoglutarate
B) Pyruvate
C) Glyceraldehyde
D) Acetyl CoA
E) All of these are entry points for amino acid catabolism.

Answer 2

Glyceraldehyde

Question 3

Consider the deamination of serine to answer the following questions.
a)Draw the structure of the α-keto acid produced by the deamination of serine.
b)What is the fate of the amino group in serine when this conversion occurs in a mammalian system?

Answer 3

a) b)The amino group is removed in the deamination as ammonia. The ammonia is in turn converted into urea and excreted during the urea cycle.

Question 4

Suppose that the formation of a dipeptide is endergonic by +14.7 kJ/mol. If this reaction is coupled with the hydrolysis of ATP, will the net reaction be spontaneous or nonspontaneous? Explain your answer.

Question 5

The coenzyme pyridoxal phosphate (PLP) in its active form has all the following characteristics except:

A) It is covalently bonded to its enzyme.
B) It possesses a phosphate group.
C) It bonds to an amine group by means of the phosphate group.
D) All of these characteristics are true.
E) All of these characteristics are false.

Question 6

Many biological reactions are endergonic. Explain how it is possible that these reactions occur spontaneously.

Question 7

This many ATP equivalents are required to produce one molecule of urea from ammonia:

A) One ATP equivalent.
B) Two ATP equivalents.
C) Three ATP equivalents.
D) Four ATP equivalents.
E) Six ATP equivalents.

Question 8

Draw the structure of the product formed when the substance shown below undergoes amide formation.

Question 9

What product would be obtained from enzymatic transamination of 3-hydroxy-2-ketopropanoic acid?

Question 10

The carbon skeletons of specific amino acids cannot be used to replenish which of the following species associated with the citric acid cycle?

A) pyruvate
B) citrate
C) fumarate
D) succinyl CoA
E) all of these can be used

Question 11

The formation of amino acids from proteins

A) occurs during anabolism.
B) is endergonic.
C) occurs during digestion.
D) is a cellular process.
E) all of these

Question 12

3-Phosphoglycerate contains the carbon skeleton used to make

A) serine
B) cysteine
C) glycine
D) all of these

Question 13

The two nitrogens in urea arise directly from:

A) Ammonia and aspartic acid
B) Carbamoyl phosphate and glutamic acid
C) Ammonia and glutamic acid
D) Carbamoyl phosphate and glutamine

Question 14

Glucogenic amino acids include all of the following, except:

A) Glycine
B) Alanine
C) Aspartic acid
D) Leucine
E) All of these amino acids are glucogenic.

Question 15

The key functional group in the PLP-dependent transamination of an α-amino acid is an activated

A) amine
B) imine
C) amide
D) enamine

Question 16

By a simple transamination reaction, intermediates in the Citric Acid Cycle can be converted in one step to all of these amino acids, except:

A) Alanine
B) Aspartic acid
C) Glutamic acid
D) Cysteine
E) All of these amino acids are only one step away from the major metabolic pathways.

Question 17

The reaction, 2 NH₄⁺ + α-ketoglutarate + NADPH + ATP → glutamine + NADP⁺ + ADP + P_i + H₂O, is the combined result of what two enzymes?

A) nitrogenase and glutamate dehydrogenase (GDH)
B) GDH and glutamine synthetase (GS)
C) GS and nitrogenase
D) GDH and nitrogenase
E) all of these are correct

Question 18

Which of the following is not an intermediate in the urea cycle?

A) arginine
B) citrulline
C) ornithine
D) lysine

Question 19

The following shows a part of the biosynthetic pathway of amino acids. If possible, draw an arrow to match the amino acid with its precursor.

Question 20

A coenzyme frequently encountered in transamination reactions is

A) tetrahydrofolate
B) pyridoxal phosphate
C) thiamine pyrophosphate
D) biotin

Question 21

Write a mechanism for the nonenzymatic transformation of glutamate semialdehyde into 1-pyrroline-5-carboxylate. Which amino acid is synthesized from 1-pyrroline-5-carboxylate in vivo?

Question 22

Write a mechanism for the formation of α-iminoglutarate from glutamate employing NAD⁺ as the oxidizing coenzyme.

Question 23

Aspartate is formed from transamination of:

A) asparagine
B) aspartame
C) oxaloacetate
D) citrate
E) α-ketoglutarate

Question 24

All of the following are true of transamination except:

A) It is characterized by the transfer of an α-amino group from an amino acid to the α-keto position of an α-keto acid.
B) The amino donor becomes an α-keto acid.
C) The coenzyme needed is thiamine diphosphate.
D) The α-keto acid acceptor becomes an α-amino acid.

Question 25

The appropriate sequence in the biosynthesis of proline from glutamate is: 1.NADPH reduction and release of P_i
2)Dehydration to 1-pyrroline-5-carboxylate
3)NADPH reduction of Schiff base
4)Phosphorylation to glutamate-5-phosphate

A) 4, 2, 1, 3
B) 4, 1, 2, 3
C) 1, 4, 3, 2
D) 1, 4, 2, 3
E) 2, 3, 1, 4

Question 26

In the process of amino acid biosynthesis, how are glutamic acid, glutamine, proline, and arginine all related?

A) They are all derived from α-ketoglutarate.
B) They are all derivatives of acetyl CoA.
C) They are all derivatives of pyruvate.
D) They are all derived from aspartate.
E) They are all derivatives of 3-phosphoglycerate.

Question 27

The term ketogenic amino acids refers to amino acids

A) that are precursors for glucose synthesis.
B) that are degraded to yield acetyl CoA or acetoacetate
C) that can not be converted to fatty acids or ketone bodies.
D) that are degraded to yield succinyl-CoA, pyruvate, α-ketoglutarate, fumarate and oxaloacetate.
E) None of these.

Question 28

Ornithine serves three metabolically important roles but is not found in proteins. Which of the following statements about ornithine is not true?

A) It is a precursor in the synthesis of citrulline.
B) It is an intermediate in the urea cycle.
C) It is a precursor in the synthesis of arginine.
D) It is biosynthesized from glutamine.
E) It is a product of arginine hydrolysis.

Question 29

All of the following are metabolic intermediates of α-amino acid carbon skeletons except:

A) pyridoxine
B) α-ketoglutarate
C) oxaloacetate
D) succinyl-CoA
E) fumarate

Question 30

Amino acids biosynthesized from aspartate include all except:

A) asparagine
B) threonine
C) methionine
D) lysine
E) glutamate

Question 31

Transamination of pyruvate with glutamate as the nitrogen donor gives:

A) alanine
B) serine
C) cysteine
D) aspartate
E) tyrosine

Question 32

What amino acid is the following α-keto acid derived from?