S/A AA, Nucleotide synthesis

Question 1

Give the overall reaction that results from the combined action of glutamate synthase and glutamine synthetase.

Answer 1

: α-Ketoglutarate + NH4+ + NADPH + ATP → glutamate + NADP+ + ADP + Pi.

Question 2

Give the equations for the two-step reaction sequence catalyzed by glutamine synthetase.

Answer 2

(1) Glutamate + ATP → γ−glutamyl phosphate + ADP. (2) γ-Glutamyl phosphate + NH4+ → glutamine + Pi + H+.

Question 3

Why is it necessary to have protein in our (human) diets?

Answer 3

Protein provides the 10 essential amino acids that humans cannot synthesize. We need these amino acids for protein synthesis and for the production of a variety of products, such as histamine and serotonin, derived from the essential amino acids.

Question 4

Describe and contrast, with diagrams, concerted (cumulative) feedback regulation and sequential feedback inhibition.

Answer 4

s: Both are allosteric mechanisms to reduce the flux through a pathway when the end product(s) are present in sufficient quantities. In cumulative feedback regulation, each of several end products partially inhibits the first enzyme in the pathway. Glutamine synthetase exhibits this kind of regulation (Fig. 22-6, p. 839). Sequential feedback inhibition occurs in a branched pathway; the product of each branch inhibits the first step in that branch. When both end products are present, the last intermediate before the branch accumulates, and it feeds back on (inhibits) the first enzyme in the main path. The synthesis of AMP and GMP (Fig. 22-34, p. 866) exemplifies this mechanism.

Question 5

Draw the structure of any purine nucleotide, name it correctly, circle the atom(s) derived from glycine. Indicate with an arrow the atom(s) derived from glutamine’s amide group(s).

Answer 5

The origin of each atom in the purine ring of IMP, AMP, and GMP is shown in Fig. 22-32, p. 864. (S