2 - Proteins and Amino Acid Metabolism Flashcards
What compounds contain nitrogen?
- Amino acids
- Proteins
- CK
- Neurotransmitters
- Haem
What can Creatinine be a measure of?
- Proportional to muscle mass at a constant rate
- Indicator of renal function (raised level when damage)
What is nitrogen balance?
What is protein turnover?
What are some examples of glucogenic and ketogenic amino acids?
G: Arginine, Proline, Valine
K: Lysine and Leucine
Both: Threonine, Tryptophan
When are protein reserves mobilised?
Prolonged starvation by hormones
What is this caused by?
- Cushing’s Syndrome
- Excess cortisol (due to steroid drugs) so weaking skin structure leading to striae
Apart from diet how can amino acids be synthesised?
1.
Apart from proteins, what other important compounds are amino acids required for?
How and why is nitrogen removed from amino acids?
- Removed so the amino acids can be used in oxidative metabolism
- Transanimation or Deanimation
What is transanimation?
- Converting an amine group from an amino acid to a keto acid to form a new amino acid that can be excreted
- Most aminotransferase enzymes use a-ketoglutarate to form glutamate
- Apart from aspartate aminotransferase which uses oxaloacetate to form aspartate
What do aminotransferases need to function?
Coenzyme pyridoxal phosphate made from Vitamin B6
What are markers for the liver function test?
ALT - Alanine to Glutamate
AST - Aspartate to Glutamate
High - Viral hepatitis, autoimmune liver disease, toxic injury (death-cap mushrooms)
What is deanimation?
- Removing amino acid as free ammonia, mainly in the liver and kidney
- The keto acid produced can be used for energy
- Important for D-amino acids from plants and microorganisms
What happens to ammonia after deanimation?
Very toxic so enters the urea cycle and is excreted into the urine. Converted back to ammonia by bacteria once weed out
What are the features of urea?
- High nitrogen content
- Water soluble
- Inert
- Osmotic role in kidneys
What is the urea cycle?
- 5 Enymes involved
- Inducible not regulated
- High protein diet induces enzyme and low protein diet represses
What are risk factors for refeeding syndrome?
What can happen with defects in the urea cycle and how can you manage the symptoms?
- Autosomal recessive
- Partial loss of enzymes
- Leads to hyperammonaemia and accumulation of urea cycle intermediates
- Severely can have onset a day after birth and can die. Mild may show in childhood
What are the theories of ammonia toxicity?
Toxic to brain. Need 25-40 ummol/L
- pH effects (alkaline)
- Disruption of cerebral blood flow
- Interference with amino acid transport and protein synthesis
- Interference with TCA cycle (reacting with a-ketoglutarate to from glutamate)
- Interfering with BBB
How is nitrogen safely transported from tissues to the liver
See lecture 2 for explanation. REALLY IMPORTANT TO LEARN
What is the heel prick test?
- If left untreated, can lead to intellectual impairment but if detected can limit amino acids
- Due to loss of enzyme activity
What is phenylketonuria (PKU)?
- Most common inborn error in phenylalanine hydroxylase deficiency
- Build up of phenylketones in urine, build up of phenylalanine in tissues, lack of tyrosine
- Autosomal recessive
What is homocystinurias?
- Autosomal recessive issue with breaking down methionine
- Defect in cystathione b-synthase
- Excess of homocystine excreted in urine
- Need cysteine, vit b, folate supplements
What is gout?
Defective purine metabolism leading to increased production or uric acid. Form monosodium urate crystals which neutrophils try to phagocytose but they are killed themselves. Leads to local pain and inflammation
What are the indirect effects of alcohol consumption?`
The effect of alcohol metabolism on the CNS and the cost of alcohol can lead to poor diet with low protein and low vitamins
What are some common secondary diseases of alcohol dependence?
- Wernicke-Korsakoff Syndrome (thiamine deficiency leading to mental confusion and unsteady gait)
- Neurological Defects (malabsorption of nutrients like Vit K and pyridoxine due to damage to GI tract)
- Chronic Pancreatitis (constant pain in upper abdomen and back and weight loss)
- Type II Diabetes (hyperglycaemia and glucosuria)
What are two important signalling molecules from amino acids?
- NO from L-arginine
- Hydrogen Sulphide from L-cysteine
What are some of the signs of hyperammonaemia?
- Blurred vision, slurred speech, tremors, coma
- Due to ammonia reacting with a-ketoglutarate with glutamate dehydrogenase to form glutamate in the mitochondria. No a-ketoglutarate for TCA
Why do you get hyperammonaeima during renal failure?
Urea is not being filtered and excreted in the urine after diffusion from the liver. It is absorbed by the intestinal wall and the gut bacteria may back it down into ammonia
Why do the accumulation of phenylketones in phenyketonuria cause brain development issues?
Similar structure to pyruvate so brain uptakes it but cannot use it
Why does the build up of phenyalanine cause mental retardation?
Phenylalanine is a large neutral amino acid, saturates LNAA transporter at bbb barrier. Other LNAA are decreased in the brain so neurotransmitter synthesis is inhibited.
What is the difference between cystine and cysteine, and homocysteine and homocystine?
Cysteine = AA
Cystine = 2 x cysteine
Homocysteine = homologue of cysteine
Homocystine = 2 x homocysteine
Why does homocystinuria affect connective tissue and what condition is it mistaken for?
- Excess homocysteine damages collagen and elastin by binding to lysine residue in proteins
- Metabolites of methionine are toxic to neurones and cause neurological disfunction
- Marfans
How does the metabolism of alcohol damage the liver?
What is oxidative stress?
How is a respiratory burst produced?
How are amino acids degraded and what are the products of degradation?
What processes produce ammonia in the body?
How is ammonia transported around the body?
Ammonia is therefore used to transaminate pyruvate to produce alanine. The alanine is then transported in blood to the liver where it is converted back to pyruvate by transamination. The amino group is then fed via glutamate into urea cycle for disposal as urea and the pyruvate is used in gluconeogenesis to synthesise glucose which can be fed back to the tissues. The other amino acid utilised in a similar way is glutamine. Ammonia is combined with glutamate to form glutamine. Glutamine is then transported in blood to the liver or kidneys where it is cleaved by glutaminase to reform glutamate and ammonia. In liver the ammonia is fed into urea cycle for disposal as urea whereas in the kidney it is excreted directly in urine.
