Protein + Amino Acid Metabolism Flashcards
Name four major N containing compounds
Amino acids
Proteins
Purine + Pyrimidines (RNA/DNA)
Creatine phosphate
What is the breakdown product of creatine and creatine phosphate?
Creatinine
Where is creatine and creatine phosphate broken down?
The muscle
What is the creatinine excretion in the urine proportional to?
Muscle mass
What is creatinine excretion in the urine also an indicator of?
Renal function
What does a positive N balance mean?
What does it indicate about body protein?
When does it occur?
Intake>output
Increase in total body protein
Growth, pregnancy, recovering from malnutrition
What does a negative N balance mean?
What does it indicate about body protein?
When does it occur?
Intake<output
Net loss of body protein
Not normal - trauma, infection, malnutrition
When does mobilisation of protein reserves occur?
Extreme stress - starvation
What is the mobilisation of protein reserves controlled by?
Give three examples
Hormones
Insulin, growth hormones, glucocorticoids
Which hormones increase protein synthesis and decrease protein degradation?
Vice versa
Insulin and growth hormones
Glucocorticoids
What is the syndrome that there is excessive breakdown of proteins?
Cushing’s syndrome
What is formed in Cushing’s syndrome?
Striae
What does it mean when amino acids are conditionally essential?
Can synthesise but may need to consume when demands increase
Where do C atoms come from for amino acid synthesis?
Glycolysis
Pentose phosphate pathway
Krebs cycle
Where can an amino group be sourced by other amino acids? (2)
Transamination - transfer of an amino acid from one molecule to another
From ammonia
What are the two things that could happen to N once removed?
Incorporated into other compounds
Excreted as urea
What are the two main pathways that facilitate the removal of N from amino acids?
Transamination
Delaminating
Why does an amine group sometimes need to be removed from an amino acid?
So the C skeleton can be used to give energy
Why does amine need to be excreted?
Otherwise it will produce ammonia
Describe Transamination
Amine group swapped for a keto group
What enzyme is used is Transamination?
Aminotransferase
What do aminotransferase enzymes used to funnel an amino group to glutamate?
Alpha ketoglutarate
What do aminotransferases require?
What is it derived from?
Coenzyme pyridoxal phosphate
Vitamin B
Name two key aminotransferases
ALT - alanine aminotransferase
AST - aspartate aminotransferase
What does plasma ALT and AST levels show?
Liver function
What does ALT do?
Catalyses inter conversion of alanine and alpha-ketogluratate to pyruvate and glutamate
What does AST do?
Catalyses inter conversion of aspartate and alpha-ketoglutarate to oxaloacetate and glutamate
What occurs in deamination?
Where does it occur?
Liberates amino group as free ammonia
Liver and kidneys
Why is deamination important?
Keto acids can be utilised for energy
Why is ammonia removed?
How?
Very toxic
Converted to urea or excreted directly in urine
Describe ureas:
N content
Toxicity
Solubility
Reactivity
High
Non-toxic
Water soluble
Inert
What happens to urea?
Excreted in urine
Osmotic role in kidney tubules
Where does the urea cycle occur?
Using how many enzymes?
Liver
Five
What increases and decreases levels of the urea cycle?
High protein diet - induces enzymes
Low protein diet or starvation - represses enzymes
What causes a defect in the urea cycle?
Autosomal recessive genetic disorder
Deficient in one of the enzymes
What can defects in the urea cycle cause?
Hyperammonaemia
Accumulation of urea cycle intermediates
Symptoms of defects in the urea cycle
Vomiting
Lethargy
Irritability
Mental retardation
Seizures
Coma
How do you manage defects in the urea cycle?
Low protein diet
Replace amino acids in diet with keto acids
What are some protential toxic effects of ammonia?
PH effects
Interferes with amino acid transport and protein synthesis
Alteration of blood brain barrier
What are two molecules that allow ammonia to be transported safely?
Glutamate
Alanine
Describe how glutamate assists the transport of ammonia
Ammonia combined with glutamate - forms glutamine
Glutamine transported in blood to liver or kidneys
Glutamine cleaved by glutaminase - reforms ammonia and glutamate
Liver - ammonia into urea cycle
Kidneys - excreted in urine
Describe how alanine is involved in ammonia transport
Ammonia combined with pyruvate - forms alanine
Alanine transported in the blood to the liver
Alanine converted back by transamination
Amino group into urea cycle
