Amino Acid Metabolism And Protein Turnover

Question 0

What is the important of amino acids?

Answer 0

• building blocks of protein
• can be sources of energy (you have to remove the N group before = deamination)
• source of glucose via gluconeogenesis

Question 1

Peptide bonds

Answer 1

2 amino acids joined together = dipeptide
3 amino acids= tripeptide etc
-can choose from 20 diff amino acids
Joining them all up you eventually end up with a protein :)

Question 2

What’s the difference between essential and non essential amino acids?

Answer 2

Essential aa can’t be made in body so must be ingested.

Non essential aa can be made in the body from other protein precursors

Question 3

Protein degredation

Answer 3

Animals have 2 sources if amino acids to replenish amino acid supplies through:
1) diet through digestion and absorption
2) or you can get them from breaking down protein in body
When dietary protein is limited then endogenous proteins are catabolised (made).
Body always tries to conserve protein, above only Happens during starvation

Question 4

Chemical signals for degredation if proteins

1) ubiquination

Answer 4

ATP dependant reaction of ubiquitin with lysine.
Your body identifies dysfunctional proteins, body then tags them with ubiquitin. Proteozomes pick up on these tags and break them down and release these small peptide groups as amino acids.
NOT regulated

Question 5

Chemical signals for degredation if proteins
Alternative regulated pathways is
2) lysosomal pathway
What’s its hormonal regulators?

Answer 5

-ATP independant
-can be cranked up and down during well fed state or starvation
Hormonal regulators:
-glucagon (+)
-insulin (-) slows degredative pathway down
-glucocorticoids (+)

Question 6

Tell me what will happen to the amino acids in this scenario?
High protein intakes
Low protein intakes

Answer 6

High dietary protein intakes ➡ plasma aa conc. high➡ aa catabolising enzymes: high Km (mM) high activity ➡ high rates of aa catabolism

Low dietary protein intake ➡low aa conc.➡ amino acyl-tRNA enzymes (takes aa and builds into proteins) : low Km constantly activite coz low Km ➡ protein synthesis

Question 7

Starvation response

Answer 7

-no intake of amino acids (not topping up amino acid pool)
-so body will grab body protein, bring aa into the pool
-deamination, release of carbon compound. Then can be used for 3 things:
-glucose synthesis, energy production, fat synthesis
-the nitrogen being freed up is being excreted as urea.
Therefore during starvation you will see elevated levels of nitrogen excretion.

Question 8

High protein diet scenario

Answer 8

-heaps adding to aa pool bigger
-accelerated deamination
-extra nitrogen to urea synthesis
-extra carbon which you will feed into glucose and fat synthesis.
-you will get fat and wee yellow if you take aa supplements
The enzymes involved have high Km so increase in their expression in high protein diet

Question 9

Low protein diet

Answer 9

• low amounts of aa in pool
• reduced amount of deamination because the deamination enzymes have a high Km.
• will get constant rate or proteins turnover
• little nitrogen excretion.

Question 10

What are the hormonal regulators and nutritional regulators of the lysosomal pathway of protein degradation?

Answer 10

Hormonal regulators: 
Glucagon stimulates 
Insulin inhibits 
Glucocorticoids stimulates 
Regulated and ATP independent 

Nutritional regulators: lysosomes
-asparagine and glutamate both inhibit protein degradation

So what happens:
-extra cellular membrane-associated or long lived proteins ➡ are internalised to lysosomes and degraded by cathepsins➡ amino acids are released for new protein synthesis.

Question 11

Lysosomal pathway of protein degradation I’m cats. Bit different to ours

Answer 11

Hormonal regulators:
-in cats glucocorticoids don’t have a stimulators effect

Nutritional:
-in cats asparagine and glutamine have no negative effect
It’s leucine and phenylalanie and tryptophan which have the strongest negative effect

This is a regulated pathway

Protein degradation I’m cat liver cells is not responsive to hormones such as glucagon and glucocorticoids

• mixture of essential amino acids most effective inhibitors of protein degradation in the cat
• cats have a greater reliance on extra-lysosomal pathway of protein degradation.

Question 12

What is the basis for a cats high protein requirement?

Answer 12

1. Inability of enzymes involved in amino acid catabolism in the cats liver to adapt to changes in dietary protein intake
2. Decreased capacity to regulate protein degradation
   - low reliance of lysosomal pathways
   - increased throughput in ubiquitin pathway