1.2 Protein And Amino Acid Metabolism Flashcards
How is creatinine used a a clinical marker?
- breakdown product of creatine and creatine phosphate in muscle
- usually produced at a constant rate unless muscle is wasting
- amount excreted in urine is proportional to muscle mass
- raised if there is damage to nephrons = can indicate renal function
When would you have a positive nitrogen balance and a negative nitrogen balance?
- Positive (intake>output) during growth or pregnancy. Get an increase in total body protein
- negative (output>intake) never normal. Causes = trauma, infection, malnutrition.
Normally should have N equilibrium
Name one.
- glucogenic
- ketogenic
- both glucogenic and ketogenic
Amino acid
- glucogenic: glycine
- ketogenic : lysine
- both: isoleucine
NB: glucogenic amino acids go to gluconeogenesis, ketogenic go to ketone bodies, both help with energy
What effects do insulin and glucocorticoid’s such as cortisol each respectively have on protein synthesis?
What does this show about mobilisation of protein reserves?
- insulin increases protein synthesis
- glucocorticoids decrease protein synthesis and increase protein segregation
Mobilisation of protein reserves is under hormonal control.
What syndrome can excessive breakdown of protein occur?
- Cushing’s syndrome
- have excess cortisol
- weaken skin structure leading to formation of purple striae
What are the 9 essential amino acids we have to consume through our diet?
Isoleucine Lysine Threonine Histidine Leucine Methionine Phenylalanine Tryptophan Valine
If learnt this huge list may prove truly valuable
Can get protein through meat diets but plants are poor source = need a wide variety of plant sources in veggies diet.
Why do amino groups (-NH2) need to be removed from amino acids?
- essential to allow carbon skeleton of amino acids to be used in oxidative metabolism
- once removed nitrogen can be incorporated into other compounds or excreted as urea
How is the amino group removed from amino acids?
1) transamination
- amino group is transferred to glutamate using alpha-ketoglutarate. A aminotransferase is used.
- amino acid becomes a keto acid.
- sometimes an aspartate aminotransferase is used to move amino group from amino acid to form aspartate. Oxloacetate is used instead.
2) De amination
- liberates amino group as free ammonia which must be removed - converted to urea and excreted
- mainly occurs in liver and kidney
- keto acids are used for energy
What are the key aminotransferase enzymes and what do they do? Also, what can they indicate?
Alanine aminotransferase (ALT) converts alanine to glutamate
Aspartate aminotransferase (AST) converts glutamate to aspartate
They can indicate liver function. High levels show cellular necrosis in conditions such as
- viral hepatitis
- autoimmune liver disease
- toxic injury
What is the urea cycle?
- a way dispose ammonia
- occours in the liver and involved 5 enzymes
- amount of urea cycle enzymes normally related to need to dispose of ammonia
- high protein diet induces enzyme levels
- low protein diet represses levels
what is refeeding Syndrome?
- occur when giving nutritional support to malnourished patients
- can get ammonia toxicity if you overwhelm urea cycle as enzymes aren’t sure to it = gradually activate them
What are the symptoms of urea cycle deficiency and when is it detected?
How can you manage it?
Symptoms
- vomiting
- mental retardation
- seizure
- Coma
Severe urea cycle disorders show within 1 day after birth. If untreated, child will die.
Management
- low protein diet
- replace amino acids in diet with keto acids
Why is ammonia toxic? What it do?
Readily diffusible and extremely toxic to the brain.
Can:
- interfere with amino acid transfer and protein synthesis
- effect pH
- disrupt cerebral blood flow
- alteration of blood-brain Barrie
What two mechanisms are utilised for the safe transport of amino acid nitrogen from tissue to the liver for disposal?
1) Glutamine
- Ammonia combined with glutamate to form glutamaine
- glutamine transported in blood to liver or kidneys where it is cleaved by glutaminase to reform glutamate and ammonia
- in liver, ammonia is fed into urea cycle. In kidney, excreted directly in urine
2) alanine
- amine groups transferred to glutamate by transamination
- pyruvate then transaminated by glutamate to form alanine
- alanine goes to liver where it becomes pyruvate again by transamination
- amino group fed via glutamate into urea cycle for disposal. Pyruvate used to make glucose which is fed back to tissues.
What is the heel prick test?
Done to newborns to test for illness/disease E.g amino acid metabolism, Sickle cell disease Cystic fibrosis Congenital hypothyroidism
