Nitrogen Flashcards
Why is nitrogen highly unreactive?
Triple bond requires lots of energy to break.
What is the nitrogen triple bond usually broken by?
Lightning (natural) Haber process (synthetic)
What enzyme does nitrogen fixation require?
Nitrogenase.
What is nitrogenase?
An enzyme required for nitrogen fixation.
What conditions does nitrogenase exist in why?
Anaerobic conditions- inactivated by oxygen.
Why does nitrogenase exist in anaerobic conditions?
It is inactivated by oxygen.
What molecule allows the flow of nitrogen in the body from NH4+ to other biomolecules?
Glutamate.
What does glutamate do?
Allows the flow of nitrogen in the body from NH4+ to other biomolecules.
What is glutamate produced by?
Alpha-ketoglutarate.
What is alpha-ketoglutarate?
Citric acid cycle intermediate which produces glutamate.
Why is nitrogen conserved in organisms?
Because most organisms cannot fix it themselves.
What is assimilation?
Nitrogen assimilation is the process by which nitrogen is conserved in organisms.
What is nitrogen transamination?
Transamination is the transfer of amino groups between different molecules in order for nitrogen to be conserved.
Is there a net gain/loss of nitrogen in transamination?
No net gain or loss because the same amount is just transferred between molecules.
Is transamination reversible?
Yes- the process is readily reversible.
What is often one of the 2 substrate pairs within transamination?
Glutamate.
What do transaminases often participate in due to amine reversibility?
Amino acid synthesis and degradation.
What enzyme is required in transamination?
Aminotransferases.
What do aminotransferases rely on?
PLP cofactor.
What is PLP?
Pyridoxal phosphate cofactor- transfers the amino group during transamination.
Why is PLP relied on by aminotransferases?
It is the cofactor that actually transfers the amino groups.
What accepts amino groups?
Alpha-ketoglutarate
What can act as a temporary store of amino groups?
L-glutamine.
What can donate the nitrogen group when needed for amino acid biosynthesis?
L-glutamine.
What does alpha-ketoglutarate do?
Accepts amino groups.
Also produces glutamate.
What does L-glutamine do?
Acts as a temporary store of amino groups and can donate the nitrogen group when required for amino acid biosynthesis.
Where do aminotransferases exist?
Intracellullar.
What does the presence of aminotransferases in the plasma indicate?
Cell damage as they are an intracellular enzyme.
Do all organisms use amino acids as a source of energy?
No- primary source within carnivores but herbivores rarely use them.
When are amino acids oxidised?
When they are in excess, in starvation (when proteins have been broken down), and when dietary amino acids are degraded.
What gives a steady flow of amino acids?
Digestion of proteins in the intestine and degradation of proteins in cells.
How are amino acids freed in the stomach?
Acidic environment and enzymes.
How are amino acids further degraded in the intestine?
Aminopeptidases degrade them further (membrane-bound proteins).
How do humans excrete ammonia?
Urea (from amino acids) Uric acid (from purines)
Where does urea come from?
Amino acids.
Where does uric acid come from?
Purines.
How is ammonia transported in the bloodstream?
Glutamine.
Where is excess glutamine produced?
Intestines, liver, kidney.
How does glutamate act on pyruvate?
Glutamate can donate ammonia to pyruvate which produces alanine. This prevents the build-up of lactic acid and reduces muscle pain and fatigue.
What does the conversion of pyruvate to alanine require?
Donation of ammonia from glutamate.
What does the conversion of pyruvate to alanine result in?
Reduced build-up of lactic acid and decreased fatigue/muscle pain.
What happens to alanine`?
Direct transport for metabolism in the liver.
Why are amino acids travelling in the bloodstream as glutamine/alanine converted back into glutamate?
Glutamine and alanine have no charge whereas glutamate is negatively charged so glutamine/alanine are used to permeate the membranes.
What charge does glutamate have?
Negative.
What charge do glutamine/alanine have?
No charge- can permeate the cell membrane.
Where is excess glutamate metabolised?
Mitochondria of hepatocytes.
What is the first nitrogen-acquiring reaction?
Recapture of ammonia through synthesis of carbamoyl phosphate.
The synthesis of what product allows the recapture of ammonia in the first nitrogen-acquiring reaction?
Carbamoyl phosphate.
What is the second nitrogen-acquiring reaction?
The nitrogen from carbamoyl phosphate enters the urea cycle as aspartate.
What does the nitrogen from carbamoyl phosphate enter the urea cycle as?
Aspartate.
What are carbon skeletons?
Carbon skeletons are the bit of the amino acid left when amino nitrogen group is removed.
What happens to carbon skeletons?
They are either converted into glucose or oxidised as part of the citric acid cycle.
How are carbon skeletons converted into glucose?
Feed back into gluconeogenesis- produce glucose or glycogen in the liver.
What are carbon skeletons that feed back into gluconeogenesis called?
Gluconeogenetic.
How are carbon skeletons oxidised as part of the citric acid cycle?
Feed into acetoacetate or acetyl CoA-
What are carbon skeletons that feed into the citric acid cycle for oxidation called?
Ketogenic.
Can ketogenic carbon skeletons contribute to gluconeogenesis?
No- this is because the pyruvate > acetyl CoA is reversible.
What are inherited metabolic disorders?
Inherited metabolic disorders are groups of individual diseases involving metabolic defects.
Are inherited metabolic disorders common?
They are individually rare but collectively quite common.
What are inherited metabolic disorders caused by?
Single gene defects.
How do inherited metabolic disorders present clinically?
Clinically severe symptoms, typically present in childhood.
What type of inheritance do inherited metabolic disorders usually show?
Autosomal recessive inheritance.
What do inherited metabolic disorders often show defects in?
Enzyme defects.
What clinical features do enzyme defects within IMDs usually show?
Acidosis, failure to thrive, vomiting, irritability, feed refusal, CNS dysfunction, hypoglycaemia, unusual order.
What characterises urea cycle defects?
More common in X-linked inheritance, rare, characterised by hyperammonaemia (elevated ammonia in blood).
What is PKU?
Amino acid disorder in which there is an absence or deficiency in phenylalanine hydroxyls which breaks down phenylalanine.
What does high phenylalanine lead to?
Developmental issues.
How is PKU treated?
Reduced protein diet supplemented with tyrosine.
What does treatment of inherited metabolic disorders require?
Integration of clinician and laboratory.
