amino acid metabolism

Question 1

Are amino acids stored and are they excreted?

Answer 1

No, excess aren’t stored since there isn’t a storage molecule for them.
Excess aren’t excreted either.

Question 2

What happens to excess amino acids to avoid wasting them?

Answer 2

Nitrogen balance - refers to levels of amino acids in the body.

There’s an amino acid pool (free amino acids floating in the blood in the extracellular fluid in cytoplasm that don’t do anything but are available to make body protein, once made into protein, degradation also occurs so that the body doesn’t get bigger and bigger each day) 250-300g/day

Or they will be broken down and not exist as amino acids anymore (100g/day)

Question 3

Describe the breakdown of an amino acid

Answer 3

1) Amine group is chopped off
left with C, H, O molecule with the R group known as carbon skeleton

2) Carbon skeleton can be broken down into CO2 and water

3) or they can be converted into purines, pyrimidines, haem etc)

Question 4

Describe the process of transamination and deamination of an amino group

Answer 4

1. TRANSAMINATION:
   Amino group from the amino acid is added onto a-ketoglutarate (using aminotransferase enzyme) to make glutamate. (e.g alanine can be used to make pyruvate)
2. DEAMINATION:
   Remove amino group from glutamate to revert it back to a-ketoglutarate. Comes off in the form of ammonium ion. Occurs in the mitochondria. Activated by ADP and inhibited by GTP.
3. The ammonium is dealt with by converting it to urea

Question 5

Aminotransferases use a ____ derived prosthetic group called _____ to do the amino group transfer

Answer 5

1. vit b6
2. Pyridoxal Phosphate (PLP)

Question 6

Urea synthesis

Answer 6

The ammonium released reacts with CO2 + H2o + 2ATP in the mitochondrion.

This makes carbomyl phosphate this the goes into the urea cycle

Question 7

Describe the urea cycle (diagram in ON)

Answer 7

Carbamyl phosphate converts ornitihine to citrulline (and releases Pi).

Citrulline reacts with Aspartate creating argino succinate.

Arginine succinate is cleaved to create fumarate (goes into TCA cycle) and arginine

Arginine is hydrolysed which cleaves off UREA and is converted into ornithine.

Question 8

How to get rid of the sulfer in some of the amino acids (Cysteine and methionine). Not expected to learn these two pathways, just get the jist.

Answer 8

Methionine sulfer is used to make cysteine.

Cysteine + O2 > Cysteinesulphinate > Transamination, B-Sulphinylpyruvate > breaks off SO2 lost in urine to make Pyruvate

OR transaminate first

Cysteine> Transamination, B-mercaptopyruvate, SH cleaved off as H2S, gives pyruvate

Question 9

What does a build up of homocysteine mean?

Answer 9

Associated with heart disease. So need to make sure there’s a lot of Vit B6 in diet