Nitrogen Metabolism Flashcards
What is creatinine and how is it used clinically?
Creatinine is the breakdown product of creatine and creatine phosphate in muscle
It’s used as an estimate for muscle mass and an indicator of renal function
What is Nitrogen balance?
Nitrogen balance refers to the relationship between nitrogen going in and going out the body
What are the three nitrogen balance types?
1) N-equilibrium (intake=output)
2) Positive N balance (intake>output)
3) Negative N balance (intake
When is positive N balance normal?
Normal state for growth and pregnancy
What is protein turnover?
Protein turnover refers to the continuous breakdown and re-synthesis of proteins
Define what the term ‘Glucogenic’ and give an example
Amino acids that can be used for gluconeogensis e.g. valine
Define the term ‘ketogenic’ and give an example
Amino acids that produce Acetyl~CoA that is used to synthesise ketone bodies e.g. Leucine
Give an example of an amino acid that is both glucogenic and ketogenic
Isoleucine
Name the hormones involved in protein reserve mobilisation under starvation and their effects
- Insulin & growth hormone = increase protein synthesis and decrease degradation
- glucocorticoids (e.g. cortisol) = decrease protein synthesis and increase degradation
What is Cushing’s syndrome?
Th excessive breakdown of protein due to excess cortisol.
Leads to striae formation - purple stripes (typically in the abdomen)
How are non-essential amino acids synthesised?
- Carbon from glycolysis intermediates, pentose phosphate pathway and kerbs cycle
- amino group from other amino acids by transamination
Define ‘transamination’ and give the basic equation
Transamination is the transfer of an amino group from one molecule to another
Amino acid 1 + Keto acid 2 = Amino acid 2 + Keto acid 1
What is the broad term used for the enzymes used in transamination?
Aminotransferases (transaminase)
What does Alanine aminotransferase do?
Convert Alanine to Glutamate
What does Aspartate aminotransferase do?
Convert Aspartate to Glutamate
Define the term ‘deamination’ and give an example of an enzyme involved
Deamination is the removal of an amino group and is turned to ammonia. Uses glutaminase, glutamate dehydrogenase, amino acid oxidases
Why is ammonia toxic?
Ammonia is readily diffusible
Many toxic effects e.g. alteration of blood-brain barrier, interfere with TCA cycle, pH effects, disruption of cerebral flow
How is ammonia transported into the liver?
1) Glutamine = ammonia + glutamate
- transported in blood to liver where it is cleaved back to ammonia and glutamate
2) Alanine = transamination of pyruvate with glutamate
- amino group fed via glutamate into the cycle
Glutamate readily goes into urea cycle
Give examples of diseases detected by the heel prick test
- Sickle dell disease
- Cystic fibrosis
- Hypothyroididm
- PKU
- Maple syrup ruin disease
- Homocystinuria
When is the heel prick test conducted?
Usually after 5 days after birth
What is Phenylketonuria (PKU)?
- An autosomal recessive disease that leads to the deficiency in phenylalanine hydroxylase
- Accumulation of phenylalanine and phenylketones in urine
What does phenylalanine hydroxylase do?
Convert Phenylalanine to Tyrosine
What is Tyrosine used for?
- Noradrenaline
- Adrenaline
- Dopamine
- Melanin
- Thyroid hormone
- Protein synthesis
Give symptoms of PKU
- Severe intellectual disability
- Developmental delay
- Microcephaly
- Seizures
- Hypopigmentation
Give treatment for PKU
- Low Phenylalanine diet
- High Tyrosine diet
- Avoid high protein diet
What is homocystinuria?
- Autosomal recessive disease that leads to cystathionine beta-synthase
- accumulation of homocysteine and methionine
What does cystathionine beta-synthase do?
Converts homocysteine to cystathionine
Give treatments for homocytinuria
- Low Methionine diet
- High Cysteine diet
- vitamin B6 supplements (cofactor)
