protein metabolism Flashcards
how much protein will a person contain?
about 1/7 of their weight in kg (over 1/2 of which in skeletal muscle)
what is the continual turnover of proteins per day?
and what is meant by protein turnover?
about 300g
constant use and restoration of protein (between amino acids to protein)
what is muscle protein synthesis?
building up of amino acids into a functioning muscle
what is muscle protein breakdown?
degradation of polypeptide chains (string of amino acids joined by peptide bonds) within muscle
what is meant by net balance?
how to calculate it?
relationship between synthesis and breakdown
net protein balance = protein synthesis - protein breakdown
when will protein and hence muscle be gained?
when the amount of protein synthesis exceeds the amount of protein breakdown
= net positive protein balance
to gain muscle have to always be in this state
does protein turnover always = net balance?
what are they both?
give an example of how they are different?
no
turnover is just what is happening with protein (not looking at whether balancing)
if more synthesis, increase in positive protein balance (net balance) but also increase in turnover (total of what is happening/activity has increased compared to steady state)
describe protein half lifes?
they vary and some may be less than an hour (good to adapt to situations)
others e.g myofibrillar take days/weeks
what is gene expression?
what is needed for it to occur
what is meant by selective egene expression?
process by which genetic info is converted into structures and functions of a cell (requires protein modifcaion to occur)
selecting which genes need expressing in environment placed in to achieve desired outcome
describe tRNA charging?
critical step in protein translation
amino acid + ATP + tRNA to aminoacyl-tRNA + AMP + Pi
what are the 3 stages of translation? (2nd stage of protein synthesis)
1) initiation - 2 parts of ribosome attach to mRNA (requires energy) and call out to 1st tRNA molecule to attach
2) elongation - continual transfer of tRNA molecules to ribosome
peptide bond occurs between AAs and tRNA molecule drops off
3) termination - at end of mRNA at stopcodon and 2 parts of ribosomes split and it disappears
left with polypeptide chain
what is the journey of protein once it is ingested into the body?
several routes
dietary protein to amino acid pools to body proteins/any nitrogen containing compounds (some may be lost through skin and hair)
feed back into pool as can be broken down
AAs once amonia removed can form CHO and fat to use for energy
and some non-essential AAs can be made by CHO and fat
amine group converted into urea and excreted through sweat or urine
is protein stored in the body?
no, it is all functional
what will happen to proteins in a starving situation?
will be degraded (especially analine) into amino acids
amine group removed
converted to form glucose and fat
describe protein synthesis?
DNA
transcription
translation
DNA contains sense and nonsense strand
have letters relating to nucleotides (T&A and C&G)
dna will split into sense and nonsense strands (transcription)
RNA polymerases will make mRNA (has U instead of T)
take mRNA, leaves nucleus via nuclear pore and goes into cytoplasm
translation occurs - tRNA has anticodon (complimentary to mRNA)
attaches, drops off AA and unattaches
ribosome is going along mRNA and asking tRNA molecules to come in to make AA chain
continues until reach stopcodon
what is always the first amino acid in a polypeptide chain?
methionine
MET
what is transcription?
formation of complimentary strand of mRNA based on gene expression
what is translation?
process by which info along mRNA is converted into polypeptide chain
what is post-translational modification?
changes in shape, folding of amino acid chain
what are some transcription factors?
activators - promote transcription by binding onto enhancer sites to enhance transcription
coactivator proteins - send signals which help RNA polymerase to get into correct position
repressors - bind to silencor sites to stop mRNA from being made
what regulates RNA polymerase?
general factors - set general rate
specific factors - change speed of rate
what regulates the rate of transcription?
1) hormones and growth factors
have direct effect by binding to specific receptor in cell
2) secondary messengers
bind to receptors on cell membrane to cell signal
describe tRNA and amino acids?
require ATP and tRNA to get AA onto tRNA
each tRNA molecule will have specific anticodon (codes AA which joins to it) so nucleotides on mRNA have to be in right order to get correct amino acid
describe post-translational processing?
polypeptide chain free
needs processing before active
folding to form correct shape and transporting via molecular chapperones
scaffolding proteins assist once it gets to correct place
what is the relationship between exercise and muscle protein synthesis?
during exercise muscle protein synthesis increases
fractional synthetic/breakdown rate (FSR/FBR) meaning?
how do their responses to exercise compare?
how much muscle grows or breaks down in a set period of time
both increase following exercise but response of muscle protein breakdown is much less than synthesis
what occurs during exercise to muscle protein balance?
higher breakdown occuring than synthesis
net muscle protein balance therefore in negative, become less negative after exercise compared to rest
what happens to protein synthesis when increasing exercise intensity?
fractional synthetic rate increasing in young and elderly (protein synthesis) when intensity increasing
what happens to protein synthesis when lifting to failure?
higher muscle protein synthesis
reach maximal synthetic rate by going to failure regardless of weight
due to stimulating type 1 and type 2 fibres (maximise muscle protein synthesis)
what is the difference in protein synthesis during exercise between trained and untrained individuals?
muscle protein synthesis increased by 43% in untrained vs trained
only see difference in relative insensity not absolute intensity as not stressing muscle if staying at same absolute intensity e.g 50kg
what is the difference between relative and absolute intensities?
absolute - do same Watts, speed or VO2 so intensity the same pre and post training
relative - go for percentage of max so differs pre and post training as max will increase
what would happen to the absolute intensity if the individual had trained but was asked to go at the same relative intensity?
e.g asked to work at 50% which before training may mean 80kg but after training may mean 100kg as max has increased from 160 to 200kg
relative intensity stays constant but due to improved training level, absolute intensity increases
explain effect of type of exercise on muscle protein synthesis?
swimmers saw 40% increase in muscle rear deltoid synthesis following a swim workout compared to a resistance workout (doing what they’re used to)
if swim workout and resistance exercise combined, then biggest increase in rear deltoid muscle protein synthesis
what has been found in rat studies?
why can it not be generalised to humans?
protein synthesis can fall during intense exercise
but were running at marathon pace for 24h (human equivalent) and were given electric shocks if stopped so not realistic
no evidence of this response in humans
what is the difference between endurance and resistance type exercise related to muscle protein synthesis?
both stimulate muscle protein synthesis
phenotypic adaptations to each are very different (how body looks as a result)
explain why endurance and resistance based athletes have different phenotypic adaptations to exercise?
due to different types of proteins in muscle (mitochondrial, sarcoplasmic, myofibrillar) and collagen synthesising more in some exercises than others
what is the untrained myofibrillar and mitochondrial protein synthesis respoonse to endurance and resistance exercise?
myofibrillar protein synthesis:
increased in resistance and no change in endurance
mitchondrial protein synthesis:
increased more in endurance than resistance but did increase in both
what is the trained myofibrillar and mitochondrial protein synthesis response to endurance and resistance exercise?
myofibrillar protein synthesis:
higher at rest and whilst exercising in resistance training compared to untrained
slightly increased during endurance training
mitochondrial protein synthesis:
increased only during endurance training
what did a study find about muscle changes in the legs after 28 days of bed rest?
lost muscle, strength and cross sectional area in legs due to increased ratio of protein breakdown to synthesis
gained of fat in legs
what does inactivity result in regarding protein synthesis?
how can this be altered?
reduces whole body protein synthesis
but fall in muscle protein synthesis can be ameliorated if resistance training included in inactivity
relationship between muscle mass and ageing and exact figure?
and some arguments why?
muscle mass in lost with ageing, 6% per decade
- decreased protein synthesis base rate
- anabolic response to feeding/exercise (don’t respond as well)
- more inactive
- increased protein breakdown
factors for decrease in physical activity in elderly people?
and results?
- increased fatigueability and muscle weakness
- decrease in endurance capacity
- muscle wasting (cycle as muscle wasting will lead to decreased physical activity)
factors which lead to cardiovascular disease
argument against reduction in basal protein synthesis rate as a cause of reduced muscle mass?
if basal protein synthesis reduces with age, would be a physiologically impossible amount of muscle loss
if there are any changes then not detectable
what is the muscle protein synthesis response to exercise in the elderly?
increase in muscle protein synthesis after exercise compared to rest
high-intensity resistance training has shown to be successful in building muscle, strength and walking speed
does elderly muscle respond to insulin and why?
no, due to intracellular signalling defects
what will result in a positive net muscle protein balance?
nutrition combined with exercise
exercise - stimulate muscle protein synthesis but still negative balance
nutrition - ingestion of amino acids will stimulate increase in protein synthesis and create positive net protein balance
how does net protein balance change throughout the day?
how can this be adjusted with exercise?
negative when wake up
eat - positive then negative etc.
same positive and negative balance so stay the same (cancel each other out)
adding exercise makes negative part less negative and the positive parts are more positive due to increase protein synthesis (greater positive protein balance compared to negative)
can too much protein damage the kidneys?
kidneys have to do lots more work to filter out amino acids from the blood
however this is their job so unless kidney disfunction then no problem
can you have too much protein?
would be getting it from e.g lots of red meat or only protein
too much saturated fat and deficiencies in macro/micros
when should you intake protein throughout the day?
if all in evening then can only use so much then the rest excreted
eat throughout the day and not all at once
what is leucine?
branch chain amino acid
oxidised in muscle
main stimulator for protein synthesis
does protein have a high satiety?
fill you up
yes
does protein boost immunity?
has a role as cells made up of protein
what amount of protein stimulates maximal protein synthesis?
what does this depend on?
around 20g for resistance on one body part
around 40g for whole body workout
depends on amount of muscle mass activated during resistance exercise rather than total muscle mass in the body
what is meant by ‘high quality’ protein?
has all the essential amino acids in
properties of Casein?
compared to whey protein in stimulating muscle protein synthesis and lean body mass gains?
takes long to digest
from cows milk
inferior to whey in stimulating protein synthesis as contains higher amount of leucine to stimulate protein synthesis and lean body mass gains
