Protein metabolism Flashcards
Protein digestion & absorption (overview)
Stomach - proteins to polypeptides (HCL, Pepsin)
Pancreas (peptidases)
SI - polypeptides to amino acids (peptidases
absorbed as amino acids
What happens to amino acid pools
constantly synthesises into body proteins and then broken down again
what happens to excess amino acids
made into CHO or Fat
amine group comes off and is excreted as urea through urine/sweat
Amino acid structure
C H O N w/ specific R group
What effect does increase insulin have on amino acids
It arrives at the liver and is synthesised into protein and transport to tissues or is stored as CHO/Fat
What happens to amino acids when fasted (catabolic)
Amino acids/proteins broken down (amine group removed) to give CHO for energy
How do proteins enter the TCA cycle (ketogenic & Glucogenic)
Ketogenic - made into acetyl-CoA
Glucogenic - feed into all different parts of the cycle depending on the AA
name of AA wo/ nitrogen group (amine)
Alpha keto - acids
What does Transamination do
Transfers amino group from AA to alpha ketoacid in the presence of a transaminase
Why is transamination important
needed for non essential amino acid production in body - & is reversable
where does transamination occur
most tissues including muscle
2 common transamination examples
Alanine + a-Keto glutamate = pyruvate + Glutamate
Aspartate + a-Keto glutamate = oxaloacetate + Glutamate
why is alanine transamination important during exercise
can be transaminated into pyruvate in liver for energy
why is aspartate transamination important
for urea cycle function
How does oxidative deamination work
ammonia group is removed
eg Glutamate to A-ketoglutarate
Is reversible & dependant on substrate availability/requirements
where does oxidative deamination occur
in the mitochondria matrix of the liver
Why is Glutamine synthesis important
- Has 2 nitrogen’s (can remove 2 ammonia groups at once)
- the most abundant free AA in blood
- Gluconeogenic precursor
- Fuels GI & immune systems
How is nitrogen (ammonia) removed from the body
- small amounts are excreted rest enters the urea cycle (energy & enzyme regulated)
AA - Urea link
^ AA = ^ Urea
Flux is dependant on substrate supply
How does the urea cycle work (carbamoyl production)
Ammonia + Co2 = Carbamoyl phosphate (enzyme = carbamoyl phosphate synthetase)
Irreversible
How does the urea cycle work (the cycle)
Carbamoyl phosphate combined with aspartate to produce urea - uses energy (fumarate side product for TCA cycle)
Urea out via sweat/urine
Branched chain amino acids (BCAA) examples & importance
- Leucine, Isoleucine, Valine
Can be oxidised in skeleton muscle mitochondria
important for muscle protein synthesis
BCAA oxidation overview
each pathway is specific w/ enzymes
Vitamin B12 and biotin required in pathways
Products are fed into TCA cycle
How does glycogen get back into the blood from muscle (Glucose-Alanine cycle work)
Glycogen -> G-6-P -> Pyruvate -> Alanine (transamination) -> released by muscle into blood
What happens to alanine once in the blood (Glucose-Alanine cycle work)
enters the liver and undergoes transamination w/ a-ketoglutarate forming pyruvate and glutamate
Pyruvate undergoes gluconeogenesis producing glucose
What happens to glucose/glutamate produced in the liver (Glucose-Alanine cycle work)
Glucose - it is release back into the blood and transported to muscle/brain
Glutamate deaminated (ammonia excreted)
Muscle protein synthesis definition
Building up of amino acids into functioning muscle
Muscle protein breakdown definition
Degradation of polypeptide chains within a muscle
net balance definition
relationship between synthesis and breakdown
Turnover defintion
constant use and restoration of protein
Protein synthesis (PS) - protein breakdown (PB) = ?
net protein balance
PB > PS = ?
negative protein balance (protein loss)
PS > PB = ?
positive protein balance (protein gain)
What % of basal energy expenditure is used for RNA formation
20%
why do some proteins have short half-lives
enzymes only needed for a short period of time
What does selective gene expression do
determines structural and functional characteristics of various cell types
How do genes & proteins differ
genes may be expressed but proteins must be activated, modified or converted
Protein synthesis process order
- transcription
- translation
- post translational modification & protein activation
Transcription process overview
copying DNA strand to mRNA (complementary base pair)
Enzyme = RNA polymerase
How is transcriptional controlled (3 groups)
Activators - bind to enhancer sites promoting transcription
Coactivator proteins - correctly position RNA polymerase
Repressors - bind to silencer sites
How is RNA polymerase regulated?
general factors - set base rate
specific factors - interact to modulate rate
hormones
- specific (steroids) - modulate process
- Secondary messenger (cAMP) - bind to cell membrane
What does aminoacyl tRNA synthetase do?
catalyses binding of AA to appropriate tRNA (w/ ATP)
is able to proofread before releasing tRNA
3 steps of translation
Initiation
Elongation
Termination
What is translation initiation
40S + 60S ribosomal subunits + mRNA molecule building new DNA molecule
(signally proteins eg eIF2 control this process)
Common start and stop codons
Start - Met
Stop - Aug
What is translation elongation
adds AA to carboxyl terminal end of PP chain
(because anticodon of aminoacyl-tRNA recognises second codon on mRNA)
Peptide bond forms
What is translation termination
When a stop codon is reached a release factor releases the complete PP chain from the last tRNA (addition of water)
ribosomal units separate
what do the 3 tRNA sites do (A P E)
A - landing site
P - Second binding site
E - Exiting site
what does post-translational modification do
- Continue folding to make the protein functional
- Transportation
What do molecular chaperones do
help build protein 3D shape (eg heat shock proteins HSP)
What do scaffolding proteins do
take proteins across mitochondrial membrane
Why do we breakdown proteins
Quality control - remove mutants, damaged
Turnover - short life, not required
Provision of AA - energy
(a-ketoacids) , protein synthesis
How does Ubiquitin-proteosome breakdown proteins
marks a specific protein for degradation
How doe lysosomal breakdown proteins
endocytosis
How does caspases breakdown proteins
programmed cell death
how does matrix metalloproteinases
removes extracellular matrix breakdown proteins
Why is calpain used to breakdown protein in muscles
because it is calcium activated
