Nitrogen Flashcards
What is a diazetroph?
Nitrogen fixing bacteria
What enzyme is used to fix nitrogen?
Nitrogenase
What is nitrogenase inhibited by?
Oxygen
How do bacteria avoid O2 inhibiting nitrogenase?
- Live anerobically
- Uncouple mitochondria which uses up O2
- Form heterocyts whose cell walls prevent O2 entry
- Form symbiotic relationships with plants
How is ammonia stored in the body?
Through Glutamate
Can any other amino acid get its nitrogen from ammonia?
No, just glutamate
What 4 amino acids are found in higher concentrations in the body?
Glutamate, Alanine, Glutamine and Aspartate
How is nitrogen transferred to other molecules/amino acids in the body from glutamate?
Via transamination
Example of transamination?
Glutamate (N) reacting with Pyruvate to form Alanine (N) and alpha-ketoglutarate (carbon skeleton of glutamate)
Transamination happens between what two acids
An amino and a keto acid.
Feature of a keto acid?
Has a COOH and a CO ketone group.
What enzyme regulates transamination?
Aminotransferase/Transaminase
Transamination is reversible - how is this significant?
It means the reaction takes part in amino acid synthesis and degradation.
What to aminotransferases rely on to work?
Pyridoxal Phosphate Cofactor (PLP)
What does PLP do?
Transfers the amino group between molecules during the reaction
What is PLP a cofactor of/ what is it derived from?
Essential vitamin B6
What are the 3 main circumstances under which amino acid degradation/oxidation would occur?
- Excess amino acids from protein synthesis
- Excess dietary amino acids
- Proteins that are broken down to produce amino acids during starvation.
What are 3 three stages of protein digestion?
Gastric
Pancreatic
Intestinal
What happens in the gastric stage?
After HCL denatures proteins, pepsin cuts them up into peptides.
What happens in the pancreatic stage?
Pancreatic enzymes Trypsin and Chymotrypsin cut proteina and large peptides down further into free amino acids and smaller peptides. This occurs in the lumen of small intestine.
What happens in the intestinal stage?
The free amino acids are absorbed into the “portal system”.
The smaller di/tri-peptides are broken down into free amino acids by aminopeptidases in the enterocytes of the brush border
Other than dietary proteins, what other proteins can be degraded?
Unwanted proteins
Mis-folded Proteins
Foreign Proteins
How is nitrogen removed from the body?
Usually urea or uric acid
Why is nitrogen transferred from glutamate to glutamine for transport?
Glutamate has an overall net negative charge making it difficult to transport. Glutamine and Alanine are neutral.
Where is excess glutamine processed?
Mostly liver, can be kidneys or intestine too.
Why and when is pyruvate converted to alanine?
During anaerobic respiration, only glycolysis occurs. Without O2, pyruvate and subsequently lactic acid would build up.
To prevent lactic acid build up pyruvate is converted to alanine for transport to the liver.
How is pyruvate converted to alanine?
Donation of ammonia/nitrogen to pyruvate from glutamate.
What happens to alanine in the liver?
Can be converted back to pyruvate by undergoing reverse transamination with alpha keto-glutarate
What happens to pyruvate in liver?
Can be converted back to glucose via gluconeogenesis
What else is formed in the liver from reverse transamination?
Glutamate
Where is excess glutamate metabolised?
Mitochondiral matrix of hepatocyte cells
What is a hepatocyte cell?
Liver cell
How is glutamate broken down?
Via a two electron oxidation reaction
What accepts the two electrons in glutamate oxidation?
NAD+ and NADP+
What happens to the ammonia from deanimated glutamate?
Recaptured by carbamoyl phosphate which passes it onto the urea cycle eventually forming urea.
What is the secondary nitrogen aquiring reaction in the urea cycle, carbamoyl phosphate being the first?
When aspartate enters the urea cycle giving up its nitrogen
What is the fate of degraded amino acids?
After the amino group is removes, most feed into the citric acid cycle or are converted to glucose.
What causes inherited metabolic disorders?
Usually autosomal recessive inheritance
What is going on in the pathways when there is an inherited metabolic disorder?
One of the key enzymes in the steps stops working, causing potentially toxic metabolites to build up as they aren’t being degraded.
Example of a cycle not working and its clinical effects?
If an enzyme in the urea cycle stopped working, toxic ammonia would build up which stimulates the center of brain controlling how fast and deep your breathe. Can cause over-breathing resulting in high blood alkali levels leading to reduced consciousness.
