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
