Protein metabolism

Question 1

ureagenesis

Answer 1

formation of urea from amino acids

Question 2

atrophy

Answer 2

muscle reduction/loss

Question 3

order of processing dietary proteins

Answer 3

1. Stomach (hydrolysed & denatured)
   o Pepsin & hydrochloric acid initiate protein digestion
2. Small intestine (denatured & neutralised)
   o Trypsin, Chymotrypsin, Aminopeptidase & carboxypeptidase
   o Pancreas secretes pancreatic proteases & enterocyte proteases
   o Secretin = triggers release of bicarbonate (HCO3)
   o Peptide fragments & free amino acids absorbed
3. Liver (transportation)
   o Remaining amino acids enter hepatic portal vein & transported to the liver
   o ~40% used for ureagenesis for energy

Question 4

rough % of protein in men vs women

Answer 4

14-16%

Question 5

what is mTOR?

Answer 5

• mandilion target of rapamycin
• master controller of protein synthesis

Question 6

function of mTOR

Answer 6

high conc. = promotes muscle growth in the body
low conc. = repair & maintenance

Question 7

autophagy

Answer 7

recycling of damaged proteins into amino acids

Question 8

mTOR pathway

Answer 8

1. Amino acids sensed by muscle cell
2. Transported across cell membrane via SNAT2 & LAT1 (membrane proteins)
3. Amino acids stimulate protein signalling & phosphorylation via Sestrin-2 (protein)
4. mTOR activated & translocate to the lysosome to become ‘active’
5. mTOR phosphorylates several proteins
   o S6K1
   o RPS6
   o 4E-BP1
6. Initiate protein translation at ribosome (mRNA) & increases protein synthesis

Question 9

p-p70S6 Kinase

Answer 9

• downstream regulator of mTOR post-exercise
• essential for increasing translation
• inducting muscle protein synthesis

Question 10

protein muscle breakdown is driven by…

Answer 10

MuRF1 & MAFbx

Question 11

function of MuRF1 & MAFbx

Answer 11

• directs tagged proteins to the proteasome for degradation
• promotion of muscular atrophy

Question 12

net balance during fasted (during exercise) state

Answer 12

• muscle protein breakdown > protein synthesis
• negative net balance

Question 13

net balance during fed (post exercise) state

Answer 13

• protein synthesis > muscle protein breakdown
• positive net balance

Question 14

role of amino acids during Krebs/Citric Acid Cycle

Answer 14

• maintain levels of specific substrates
• maintain glucose levels

Question 15

Transamination

Answer 15

transfer of 1 amino group from 1 molecule to another

Question 16

enzymes used in transamination

Answer 16

• aminotransferase = catalyses transamination
• alpha-ketoglutarate = involved in transamination

Question 17

Deamination

Answer 17

amino acid removal & loss of its amino group

Question 18

what is produced from deamination?

Answer 18

ammonia (toxic)

Question 19

what happens to ammonia after deamination?

Answer 19

ammonia is converted into urea in the liver

Question 20

3 amino acids which bypass degradation by the liver

Answer 20

• leucine
• isoleucine
• valine

Question 21

Cori Cycle (lactate)

Answer 21

1. Lactate produced by anaerobic glycolysis in muscles
2. Transported to the liver & converted to glucose
3. Returns to the muscles & cyclically metabolized back to lactate

Question 22

The Glucose-Alanine Cycle (Alanine)

Answer 22

1. Pyruvate forms amino acid acceptor (transamination)  forms alanine
2. Alanine transported to the liver & converted to pyruvate & glutamate (used via citric acid cycle)
3. Glucose then transported back to the muscle

Question 23

4 steps in the conversion of ammonia to carbamoyl phophate

Answer 23

1. Ammonia + Ornithine  Citrulline
2. Citrulline converted to arginine succinate
3. Arginine succinate  arginine + fumarate
4. Arginine hydrolysed via arginase  urea