Muscle and Exercise Lecture 3.1 - New approaches in measuring muscle protein metabolism: the science of muscle hypertrophy Flashcards
Why is protein turnover important?
Whether a muscle hypertrophies or breaks down is dependent on protein turnover.
What do you control if you control protein turnover?
Muscle mass.
What is the daily synthesis and breakdown of protein?
~300g/day each.
What is the daily oxidation of protein, and what should onés intake be?
~80g/day each.
Are proteins the sole source of energy? How much do they contribute?
No, play only a minor role.
If muscles are 100% efficient, will contribute up to 50%.
How can you measure your protein balance?
If the nitrogen content of the food is known, measure nitrogen exreted in urine to estimate balance.
What is the problem with making nitrogen intake 0 in measuring protein balance?
Protein utilisation always increases when nitrogen intake is 0, so inaccurate.
What is the ideal way to measure protein balance?
Use of stable isotopes.
How can stable isotopes be used to measure transamination and aa oxidation?
Ingest radioisotope, the amount present in breath suggests oxidation levels.
Which is more highly oxidised, leucine or phenylalanine?
Leucine.
Does exercise affect phenylalanine oxidation?
No.
Does exercise increase leucine oxidation?
Yes.
How can stable isotopes be used to measure protein synthesis?
Ingest isotope, then take muscle biopsy and check how much protein has isotopes. Can also isolate organelles and check incorporation.
What happens to protein synthesis levels during and after exercise?
Decreased during exercise, but increased after, for up to 48h.
What is the disadvantage of stable isotope proteins?
Tracer amino acids are very expensive.
What is an alternative to stable isotopes?
SunSET technique, using puromycin.
What does puromycin look like, and what does it do?
Looks like tRNA, and will sometimes take its place and bind to newly formed protein.
How does puromycin binding to protein evaluate protein turnover?
Antibodies against puromycin can be used in western blotting to evaluate protein turnover.
What does rapamycin do, and what is a consequence of this?
Blocks mTOR, decreasing protein synthesis.
What does mTOR do?
Main driver of protein synthesis.
How does mTOR work?
Phosphorylates 4EBP1 to allow ribosome complex formation.
What effect does AKT have on mTOR?
AKT activates mTOR, and reduces atrogin-1 transcription.
What does AKT act as?
A critical regulator of muscle mass.
If the gastrocnemius muscle is cut, what hhappens to surrounding muscle? What happen to AKT levels in them?
What about if you give rapamycin?
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.
