Metabolism 5: amino acid metabolism (Miss Dawson)

Question 1

What part of the amino acid must be removed ?

Answer 1

The amino group must be removed, either as NH3+ or transferred to another compound. Most N is used to make urea in the liver, and excreted in the urine.

Question 2

How does AA catabolism happen in various organs/tissues ?

Answer 2

Sk muscle: uses AAs as fuel, especially the branched chain AAs Ile, Leu and Val
Liver: uses AAs as fuel, especially since it is the only organ that can make urea
Small intestine: uses AAs from digestion, and from the blood, as fuel

Question 3

How do tissues that use AA often get rid of the nitrogen ?

Answer 3

They pass to the liver in the form of simple AAs e.g. Ala, Glu, Gln

Question 4

What is alanine’s fate ?

Answer 4

It is converted to pyruvate by an amino-tranferase. Alpha-keto-glutarate is converted to glutamate in the process.

Question 5

What is glutamate’s fate ?

Answer 5

It is converted to alpha-keto-glutarate by an amino-tansferase of glutamate dehydrogenase.

Question 6

What is leucine’s fate ?

Answer 6

Simliar to FAs, leucine goes through oxidation (producing NADH and FADH2), hydration and finally cleavage to form acetyl CoA (which can then enter the Krebbs cycle).

Question 7

How do key organs/tissues catabolize AAs in the fed state?

Answer 7

Sk muscle: takes up branched AAs and uses them for fuel
Liver: uses AAs for fuel, but may also use them to make glucose or fat
Small intestine: uses AAs from circulation and digestion, especially glutamine

Question 8

How do key organs/tissues catabolize AAs during starvation ?

Answer 8

Sk muscle: oxidises AAs instead of glucose and releases AAs into the blood
Liver: uses AAs for fuel, but may also use them to make glucose or ketone bodies
Small intestine: uses AAs fro circulation, especially glutamine
Brain: uses glucose and ketone bodies for fuel