Lecture 15: Protein Turnover Flashcards
What is protein turnover?
The process of continuous degradation & re-synthesis (homeostasis)
Where is the free AA pool found?
Mostly all free AA pools in the blood but some tissues & subcellular compartments
* very small pool, constant turnover
What are the two components of protein metabolism?
- protein turnover: synthesis/degradation
- nitrogen balance: N intake/output
Synthesis + Excretion = Degradation + Intake = flux rate (Q)
What are excretory losses of protein?
urine, feces, hair and skin loss, sloughing off of intestinal cells, mucus and enzyme secretions in intestine.
* requires dietary protein to replace
Describe protein balance
Anyfactorthatchangesthebalanceof synthesis & degradation (turnover) will result in positive or negative protein (N) balance
energetics of protein turnover
Energetically expensive (~10-25%ofBMR) but still neccessary
* ⇩ in turnover rate during starvation = ⇩energy use
What is the necessity of protein turnover?
Basic body functioning & adaptation
* excretion of nitrogen
* mobilization of AAs to maintain blood [glucose]
* degradation and replacement of proteins
* change relative amounts of proteins in responce to changes in nutrition and physiological conditions
What is the main site of protein degradation?
Liver which is closely linked with urea production
* muscle oxidizes branched AAs
* SI oxidizes Gln, Glu, Asp
What happens to AAs not used for protein or peptide synthesis?
no storage form so must be converted to something else
* Partially oxidized & C skeletons converted to other compounds, depending on body needs (e.g. glucose, glycogen, other AAs, TGs, cholesterol, ketone bodies)
* Converted to non-protein derivatives (e.g. creatine, heme, nucleic acids, neurotransmitters, non-peptide hormones)
once converted do not return
skeletal muscle and protein
- not a protein storage organ, reserve for gluconeogenic precursors and large for typical physiological demands
- AA mobilized to support protein synthesis and gluconeogenesis and AA taken up by skeletal following intake
- Any protein degrades leads to AAs being released into blood stream
Why is the AA pool limited?
excess is toxic
* affects transport into the brains
Why is AA oxidation, gluconeogenesis and ureagenesis all active during both fed and starved states?
required for enzymatic activity of both states?
just a guess need to find out the answer
What are the protein catabolic and anabolic signals?
- Catabolic: glucagon,thyroid hormones, glucocorticoids, catecholamines, cytokines
- Anabolic: insulin,aminoacids
What does the half-life of individual proteins depend on?
depends on the function of:
* rapid turnover of regulatory proteins = rapid ↑ or ↓ Incretin GLP-1 60 secs, Insulin 10 minutes
* Slower turnover of non-regulatory enzymes & transport proteins hemoglobin 55 days, serum albumin ~21 days
* Slowest turnover of structural proteins eg. collagen 120 days
How does lean muscle change through adulthood?
Lean muscle mass ~ 50% of total bodyweight in young adults, but ~25% by age 75– 80 years
What is the cause of age related muscle loss?
The progressive mismatch between mass and strength partly occurs because of a deterioration of muscle quality.
* degradation more than synthesis
* external factors of malnutrition and inacitivity
