NUTR3100 Exam 3 Protein in the Fed State

how much protein a day is synthesized & degraded

~300g of protein/day

humans eat

~50g of protein a day

RDA

0.8g/kg body weight

AAs come from

diet and endogenous protein degradation

protein catabolism accounts for

~25% of ATP daily

AAs used for energy production

different AAs yield diff ATP based on efficiency of metabolic rxn

20 AAs for protein synthesis

sleneocysteine is 21st, not in plants

SECIS element

selencocysteine insertion sequence

Where does protein synthesis occur in tissue?

In the cytosol on rough ER

What is required for protein function after synthesis?

Post-translational modifications

Do different tissues exhibit the same rates of protein synthesis?

No, different tissues exhibit different rates

What percentage of total protein mass in the body does skeletal muscle contain?

45%

recycling old proteins

- autophagy-lysosomal system

- ubiquitin-proteasome pathway

autophagy-lysosomal system

- targets whole organelles for recycling

- beneficial during limited nutrient availability

- degradation provides material to sustain anabolic processes including protein synthesis

mTOR

- promotes anabolic processes

- reduces autophagy (breakdown) by phosphorylating and repressing protein complex needed for initiating autophagy

mTOR is a

kinase that regulates cell growth, proliferation and survival

Ubiquitin-proteasome pathway

- activated by low nutrient availability and glucagon/epinephrine signaling through beta adrenergic receptors

insulin inhibits

mTOR which inhibits both pathways that recycle proteins

AAs that control protein synthesis

leucine, glutamine, and histidine

adequate levels of L, Q, and H

activate mTOR (which inhibits autophagy and proteosome pathways but activates protein synthesis)

glutamine is

conditionally non-essential

Amino acids are used for synthesis of

- protein and non-protein molecules

- glucose, ketones, and fatty acids

tryptophan is precursor to

serotonin

tyrosine is precursor to

thyroid hormone, melanin

arginine is precursor to

nitric oxide

glutamate, cysteine, glycine is precursor to

glutathione