Amino Acid Metabolism

Question 1

Nitrogen fixation

Answer 1

Process of reducing atmospheric N2 (non-reactive) to ammonia (nucleophilic)

Question 2

Common entry points for nitrogen in organic molecules

Answer 2

Glutamate and glutamine

Alpha-ketoglutarate + NH4 -> glutamate (enzyme: glutamate dehydrogenase)

Question 3

Transamination reaction

Answer 3

Transferring the alpha-amino group of glutamate to another molecule (typically an alpha-keto acid)

Question 4

Where are the 20 common amino acids derived from?

Answer 4

Metabolic intermediates from glycolysis, the pentose phosphate pathway, and the TCA cycle

Question 5

The urea cycle

Answer 5

Conversion of toxic ammonia to urea, which is less toxic and can be excreted
Process occurs mainly in the liver

Question 6

Net reaction of urea cycle

Answer 6

NH3 + HCO3- + aspartate + 3 ATP -> urea + fumarate + 2 ADP + 2 Pi + AMP + PPi

Question 7

Preliminary step of urea cycle

Answer 7

Synthesis of carbamoyl phosphate from bicarbonate and Pi from ATP

Question 8

Step 1 of urea cycle

Answer 8

Ornithine + carbamoyl phosphate -> citrulline

Enzyme: ornithine transcarbamoylase

Question 9

Step 2 of urea cycle

Answer 9

Citrulline + aspartate -> argininosuccinate

Enzyme: argininosuccinate synthetase

Question 10

Step 3 of urea cycle

Answer 10

Argininosuccinate -> arginine
Enzyme: argininosuccinate lyase
Fumarate is released

Question 11

Step 4 of urea cycle

Answer 11

Arginine -> urea + ornithine

Enzyme: arginase