Muscle and Exercise Lecture 3.1 - New approaches in measuring muscle protein metabolism: the science of muscle hypertrophy

Question 1

Why is protein turnover important?

Answer 1

Whether a muscle hypertrophies or breaks down is dependent on protein turnover.

Question 2

What do you control if you control protein turnover?

Answer 2

Muscle mass.

Question 3

What is the daily synthesis and breakdown of protein?

Answer 3

~300g/day each.

Question 4

What is the daily oxidation of protein, and what should onés intake be?

Answer 4

~80g/day each.

Question 5

Are proteins the sole source of energy? How much do they contribute?

Answer 5

No, play only a minor role.

If muscles are 100% efficient, will contribute up to 50%.

Question 6

How can you measure your protein balance?

Answer 6

If the nitrogen content of the food is known, measure nitrogen exreted in urine to estimate balance.

Question 7

What is the problem with making nitrogen intake 0 in measuring protein balance?

Answer 7

Protein utilisation always increases when nitrogen intake is 0, so inaccurate.

Question 8

What is the ideal way to measure protein balance?

Answer 8

Use of stable isotopes.

Question 9

How can stable isotopes be used to measure transamination and aa oxidation?

Answer 9

Ingest radioisotope, the amount present in breath suggests oxidation levels.

Question 10

Which is more highly oxidised, leucine or phenylalanine?

Answer 10

Leucine.

Question 11

Does exercise affect phenylalanine oxidation?

Answer 11

No.

Question 12

Does exercise increase leucine oxidation?

Answer 12

Yes.

Question 13

How can stable isotopes be used to measure protein synthesis?

Answer 13

Ingest isotope, then take muscle biopsy and check how much protein has isotopes. Can also isolate organelles and check incorporation.

Question 14

What happens to protein synthesis levels during and after exercise?

Answer 14

Decreased during exercise, but increased after, for up to 48h.

Question 15

What is the disadvantage of stable isotope proteins?

Answer 15

Tracer amino acids are very expensive.

Question 16

What is an alternative to stable isotopes?

Answer 16

SunSET technique, using puromycin.

Question 17

What does puromycin look like, and what does it do?

Answer 17

Looks like tRNA, and will sometimes take its place and bind to newly formed protein.

Question 18

How does puromycin binding to protein evaluate protein turnover?

Answer 18

Antibodies against puromycin can be used in western blotting to evaluate protein turnover.

Question 19

What does rapamycin do, and what is a consequence of this?

Answer 19

Blocks mTOR, decreasing protein synthesis.

Question 20

What does mTOR do?

Answer 20

Main driver of protein synthesis.

Question 21

How does mTOR work?

Answer 21

Phosphorylates 4EBP1 to allow ribosome complex formation.

Question 22

What effect does AKT have on mTOR?

Answer 22

AKT activates mTOR, and reduces atrogin-1 transcription.

Question 23

What does AKT act as?

Answer 23

A critical regulator of muscle mass.

Question 24

If the gastrocnemius muscle is cut, what hhappens to surrounding muscle? What happen to AKT levels in them?
What about if you give rapamycin?

Answer 24

Cutting gastrocnemius causes compensatory hypertrophy of other muscles.
They have upregulated levels oh phosphorylated AKT, the active form of AKT.
If rapamycin is given, no hypertrophy.

Question 25

What effect does glycine administration have on cancer cachexia wasting?

Answer 25

Can prevent up to 50% of associated muscle wasting.

Question 26

What effect does leucine have on cancer cachexia wasting?

Answer 26

No effect.