Nitrogen

Question 1

What is a diazetroph?

Answer 1

Nitrogen fixing bacteria

Question 2

What enzyme is used to fix nitrogen?

Answer 2

Nitrogenase

Question 3

What is nitrogenase inhibited by?

Answer 3

Oxygen

Question 4

How do bacteria avoid O2 inhibiting nitrogenase?

Answer 4

1. Live anerobically
2. Uncouple mitochondria which uses up O2
3. Form heterocyts whose cell walls prevent O2 entry
4. Form symbiotic relationships with plants

Question 5

How is ammonia stored in the body?

Answer 5

Through Glutamate

Question 6

Can any other amino acid get its nitrogen from ammonia?

Answer 6

No, just glutamate

Question 7

What 4 amino acids are found in higher concentrations in the body?

Answer 7

Glutamate, Alanine, Glutamine and Aspartate

Question 8

How is nitrogen transferred to other molecules/amino acids in the body from glutamate?

Answer 8

Via transamination

Question 9

Example of transamination?

Answer 9

Glutamate (N) reacting with Pyruvate to form Alanine (N) and alpha-ketoglutarate (carbon skeleton of glutamate)

Question 10

Transamination happens between what two acids

Answer 10

An amino and a keto acid.

Question 11

Feature of a keto acid?

Answer 11

Has a COOH and a CO ketone group.

Question 12

What enzyme regulates transamination?

Answer 12

Aminotransferase/Transaminase

Question 13

Transamination is reversible - how is this significant?

Answer 13

It means the reaction takes part in amino acid synthesis and degradation.

Question 14

What to aminotransferases rely on to work?

Answer 14

Pyridoxal Phosphate Cofactor (PLP)

Question 15

What does PLP do?

Answer 15

Transfers the amino group between molecules during the reaction

Question 16

What is PLP a cofactor of/ what is it derived from?

Answer 16

Essential vitamin B6

Question 17

What are the 3 main circumstances under which amino acid degradation/oxidation would occur?

Answer 17

1. Excess amino acids from protein synthesis
2. Excess dietary amino acids
3. Proteins that are broken down to produce amino acids during starvation.

Question 18

What are 3 three stages of protein digestion?

Answer 18

Gastric
Pancreatic
Intestinal

Question 19

What happens in the gastric stage?

Answer 19

After HCL denatures proteins, pepsin cuts them up into peptides.

Question 20

What happens in the pancreatic stage?

Answer 20

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.

Question 21

What happens in the intestinal stage?

Answer 21

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

Question 22

Other than dietary proteins, what other proteins can be degraded?

Answer 22

Unwanted proteins
Mis-folded Proteins
Foreign Proteins

Question 23

How is nitrogen removed from the body?

Answer 23

Usually urea or uric acid

Question 24

Why is nitrogen transferred from glutamate to glutamine for transport?

Answer 24

Glutamate has an overall net negative charge making it difficult to transport. Glutamine and Alanine are neutral.

Question 25

Where is excess glutamine processed?

Answer 25

Mostly liver, can be kidneys or intestine too.

Question 26

Why and when is pyruvate converted to alanine?

Answer 26

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.

Question 27

How is pyruvate converted to alanine?

Answer 27

Donation of ammonia/nitrogen to pyruvate from glutamate.

Question 28

What happens to alanine in the liver?

Answer 28

Can be converted back to pyruvate by undergoing reverse transamination with alpha keto-glutarate

Question 29

What happens to pyruvate in liver?

Answer 29

Can be converted back to glucose via gluconeogenesis

Question 30

What else is formed in the liver from reverse transamination?

Answer 30

Glutamate

Question 31

Where is excess glutamate metabolised?

Answer 31

Mitochondiral matrix of hepatocyte cells

Question 32

What is a hepatocyte cell?

Answer 32

Liver cell

Question 33

How is glutamate broken down?

Answer 33

Via a two electron oxidation reaction

Question 34

What accepts the two electrons in glutamate oxidation?

Answer 34

NAD+ and NADP+

Question 35

What happens to the ammonia from deanimated glutamate?

Answer 35

Recaptured by carbamoyl phosphate which passes it onto the urea cycle eventually forming urea.

Question 36

What is the secondary nitrogen aquiring reaction in the urea cycle, carbamoyl phosphate being the first?

Answer 36

When aspartate enters the urea cycle giving up its nitrogen

Question 37

What is the fate of degraded amino acids?

Answer 37

After the amino group is removes, most feed into the citric acid cycle or are converted to glucose.

Question 38

What causes inherited metabolic disorders?

Answer 38

Usually autosomal recessive inheritance

Question 39

What is going on in the pathways when there is an inherited metabolic disorder?

Answer 39

One of the key enzymes in the steps stops working, causing potentially toxic metabolites to build up as they aren’t being degraded.

Question 40

Example of a cycle not working and its clinical effects?

Answer 40

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.