Protein Flashcards
(27 cards)
terms
Muscle protein synthesis
Muscle protein breakdown
Net balance
Turnover
interaction between PS, PB and net protein balance
Protein Synthesis - Protein Breakdown = net protein balance
PB exceeds PS = negative protein balance → protein loss
PS exceeds PB = positive protein balance → protein gain
net protein balance and energy
Protein synthesis and protein breakdown are often linked
As much as 20% of basal energy exp
Formation of RNA
Make peptide chain
~300g/d turnover
Protein half-lives vary Some enzymes <1h Important to respond to changing conditions Other proteins (e.g. myofibrillar) days/weeks
why spend such energy to continually turnover proteins
Gene expression
Selective gene expression determines the structural and functional characteristics of the various
cell types
Genes may be expressed, but proteins must be activated, modified and/or converted
protein synthesis processes
Transcription
Translation
Post-translational modification and targeting to ensure proteins are activated
Complex regulation at any of these steps
transcriptional control
Transcription factors
Activators
Enhancer sites
Coactivator proteins
Signals
Repressors
Silencer
Regulation of RNA Polymerase
tRNA charging
AA + ATP + tRNA → aminoacyl-tRNA +AMP + Pi
Aminoacyl tRNA synthetase – catalyses binding of AA to appropriate tRNA
Amino acids activated by ATP
AA transfer to specific tRNA
Each tRNA has a specific anticodon
Specificity is crucial
tRNA synthetase contains proofreading site
tRNA charging is an irreversible process
processes of translation
Initiation
Elongation
Termination
initiation
The process of initiation of translation involves:
40S and 60S ribosomal subunits
mRNA molecule
the initial aminoacyl-tRNA (methionyl-tRNA) (tRNA molecule with methionine attached)
a number of protein factors to control the initiation process, e.g. p70s6 kinase, eIF4E, etc.
Energy from GTP
elongation
Involves the addition of amino acids to the carboxyl terminal end of the polypeptide chain
The process occurs because the anticodon of aminoacyl-tRNA recognises the second codon on the mRNA
A peptide bond occurs between the carboxyl group of MET and the second amino acid (which is still attached to its tRNA
termination
The process continues (three bases at a time) until a stop codon is reached.
The stop codon is recognised due to the specificity of the mRNA
A termination factor releases the complete polypeptide chain from the last tRNA and the 80S disassociates to its two 40S and 60S subunits
post-translational processing
After the polypeptide is released from the translational apparatus, it requires further processing before it is in
physiologically active form and
the cell location where it becomes functional.
A growing protein will begin to fold as it is being made and proteins have the capacity to self fold - However, many complex proteins need help to fold.
Molecular chaperones or chaperonins, e.g heat shock proteins (Hsp).
Scaffolding proteins
control sites
reg of RNA P’s
reg of translation
reg of post-translational control
reg of RNA P
Repressors
Activators
Chromatin
Histone acetylation
reg of translation
Initiation factors
Elongation factors
reg of post-translational control
Chaperones
Scaffolding proteins
3 reasons why protein limited fuel in ex
- primary role provides AA building blocks for tissue synthesis
- early studies show only minimal PB during endurance ex as reflected by urinary N excretion
- theoretical computations and exp evidence of protein requirements for muscle tissue synthesis with resistance training
what does protein as a fuel rely on?
energy expenditure and nutritional status
applies to branched chain AAs leucine, valine and isoleucine oxidised in skeletal muscle rather than in liver
after endurance and resistance type ex what happens to muscle PS?
increases
what 2 factors justify re-examining protein intake recommendations involved in ex?
increased PB during prolonged ex and intense training
increased PS in recovery
In normal healthy individuals body proteins can be excreted as?
hair
skin
Which protein breakdown system is predominantly involved in apoptosis?
caspases
muscle protein synthesis
Building up of amino acids into functioning muscle
muscle protein breakdown
Degradation of polypeptide chains within a muscle
