CH 30

Question 1

During the degradation of many amino acids, the first step involves transfer of the amino group to citric acid cycle intermediate

Answer 1

α‑ketoglutarate.

Question 2

Amino groups transferred to α‑ketoglutarate are subsequently released as the ammonium ion in a reaction catalyzed by glutamate dehydrogenase.

In this reaction, what accompanies the oxidation of the amino group to a Schiff‑base intermediate?

Answer 2

the reduction of NAD+ or NADP+

Question 3

Terrestrial vertebrates use the urea cycle to convert the ammonium ion to urea such that the urea can be excreted. In the production of urea, only one of the nitrogens in the product comes from an ammonium ion.

What is the source of the other nitrogen in urea?

Answer 3

aspartate

Question 4

The carbon skeletons of _____ directly enter metabolism at the level of pyruvate.

Answer 4

alanine and serine

Question 5

The initial step in the degradation of phenylalanine is its conversion to another of the 20 common amino acids in a reaction catalyzed by phenylalanine hydroxylase.

Answer 5

adds a phenolic −OH group, producing tyrosine

Question 6

In the conversion of phenylalanine to tyrosine, the source of the oxygen is

Answer 6

O2.

Question 7

The class of enzymes involved in nearly all cleavages of aromatic rings in biological systems is

Answer 7

dioxygenase.

Question 8

Urea can be said to directly originate from which single amino acid?

Answer 8

R