[FMS] NAM - amino acid metabolism Flashcards
what is the average adult protein turnover?
What are the body’s protein requirements?
turnover 300-400g/day
recommendation: 50 – 70 g protein per day
what is the half-life of proteins?
most proteins have half-lives of several days
structural proteins have half-lives of years
Hormones & digestive enzymes are degraded very rapidly, with half-lives of minutes.
what is the recommendation of protein daily?
50-70g
how many essential amino acids are there?
20
which 10 amino acids can the body synthesize on its own
remember “private tim hall”
P = phenylalanine
V = valine
T = threonine
T = tryptophan
I = isoleucine
M = methionine
H = histidine
A = arginine
L = leucine
L = lysine
what is nitrogen balance?
N (intake) = N (excretion)
nitrogen excretions are in what form?
- urea
- uric acid
- creatinine
- NH4+
what is a positive nitrogen balance?
N (intake) > N (excretion)
intake more than excretion
when does a positive nitrogen balance occur
- normal children growth
- convalescence after serious illness
- in pregnancy
- after immobilisation after accident
what is a negative nitrogen balance?
N (intake) < N (excretion)
excretion more than intake
when does a negative nitrogen balance occur
- in starvation
- during serious illness
- late cancer stages - cachexia
- injury and trauma
^ If not corrected and becomes prolonged, there will be irreversible loss of essential body tissue
will ultimately lead to death.
what is the pathway of protein degradation for cellular proteins
- If they are recognised as ‘old’ or damaged they are removed by the ubiquitin breakdown system
- They are a mixture of the 20 amino acids
what is the pathway of protein degradation for exogenous proteins
- ‘old’ or damaged sub cellular organelles are taken into vesicles by endocytosis, or autophagocytosis. The vesicle fuses with lysosomes and proteolytic enzymes degrade proteins into amino acids
- Starvation and hormones (e.g. cortisol increase) rates of protein breakdown in muscle
what are amino acids degraded into? ie what are amino acids made of?
It is an oxo (keto) acid with an amine group.
what are the two processes of aa degradation?
oxidative deamination and transamination
What is transamination?
transfer of the amino group of an amino acid onto a keto acid to produce the amino acid of that keto acid and the keto acid of that amino acid.
what does transmination need?
- amino acid
- keto acid
- aminotransferase with pyridoxal phosphate
outline what happens in deamination
outline what happens in transamination
remember: TRANSamination = TRANSfer
what is the fate of oxo-acids in starvation?
carbon skeletons of 13 amino acids converted back to glucsoe by liver, these are classified as ‘glucogenic’.
what are ketogenic amino acids
Leucine and lysine
^ These can only be degraded to acetyl CoA, not pyruvate
what are the 5 glucogenic and ketogenic amino acids?
phenylalanine, tyrosine, tryptophan, isoleucine, threonine
REMEMBER: PITTT
what is the difference between glucogenic and ketogenic amino acids and its ability to be converted to glucose?
glucogenic = can be converted back to glucose by liver
ketogenic = cant be converted back to glucose, can only be degraded to acetyl coA, leucine, lysine
What are the important amino acids in the inter-organ transport of nitrogen?
- Alanine - can be deaminated into pyruvate but not directly
- Glutamate - can be deaminated into pyruvate directly
- Glutamine - can be deaminated into pyruvate but not directly, goes to glutamate to alpha-ketaglutarate.
- Aspartate - can be deaminated into pyruvate but not directly, goes to oxaloacetate.
3 Important features of glutamine
safe carrier of ammonia in the blood
^ Ammonia is toxic to the brain
Glutamine can carry 2 ammonia equivalents to the liver for urea formation
Glutamine can deliver ammonium ions to the kidney for pH regulation (buffering H+)
where does urea cycle take place
cytosol/ mitochondrial matrix
explain urea cycle and enzymes involved
What are the 4 end products of nitrogen metabolism?
- Urea - protein breakdown
- Creatine - creatine phosphate breakdown
- Uric acid - DNA and RNA breakdown
- Ammonia (NH4+) - control of body pH
What does the build up of ammonia cause?
- Ammonia is neurotoxic
- The exact mechanism is not known
- It causes cerebral oedema, coma and death
- Seems to involve cell death
- How do you get an impaired conversion of NH3 to urea (hyperammonaemia)?
- Liver failure - (viral hepatitis, ischaemia, liver cirrhosis, toxins eg aflatoxin in mouldy peanuts)
- Genetic defects - reduction in catalytic activity of any enzyme of the urea cycle
what is the name of the condition for exessive ammonia concentration? what is the treatment
hyperammonaemia, treatment = dialysis
what does urea do?
protein breakdown
what does creatine do
creatine phosphate breakdown
what does uric acid do?
DNA + RNA breakdown
what does ammonia do?
body pH control
Why are alanine and aspartate transaminases important diagnostically?
They are markers for liver damage.
Plants and micro organisms can synthesise all 20 amino acids from what?
NH3 and CO2
whats the difference between what happens to glucogenic amino acids and ketogenic amino acids?
glucogenic –> goes to pyruvate, TCA
keotgenic –> goes to acetyl CoA
