Protein Turnover, Nitrogen

Question 1

Can proteins from the diet be stored?

Answer 1

No, only the carbons liberated from the AAs.

Question 2

What are the three basic steps in nitrogen metabolism?

Answer 2

1. Transfer N to a common carrier
2. Generate ammonia in liver
3. Incorporate ammonia into urea

Question 3

What is PLP and what is it used for? What vitamin is it derived from?

Answer 3

Pyridoxal phosphate - a cofactor for aminotransferases. Derived from B6

Question 4

What do aminotransferases do?

Answer 4

Transfer animo groups to carrier AAs.

Question 5

What are the three main nitrogen carriers and what do they arise from?

Answer 5

alpha-KG + N –> glutamate
OAA + N –> aspartate
pyruvate + N –> alanine

Question 6

What is the subcellular location of glutamate DH?

Answer 6

Mitochondria

Question 7

How is glutamate DH regulated?

Answer 7

GTP, ATP inhibit, ADP, GDP activate.

Question 8

What is the major nitrogen carrier in the blood?

Answer 8

Glutamine.

Question 9

In which organ does the glutamine synthase reaction occur?

Answer 9

High activity in liver.

Also in brain, muscle, lungs, adipose

Question 10

What is the limiting step of the urea cycle?

Answer 10

Carbamoyl phosphate synthesis.

Question 11

Do you know the urea cycle?

Answer 11

Yes or no.