Nitrogen metabolism

Question 1

Where does nitrogen come from?

Answer 1

Protein from the diet

Question 2

How is nitrogen stored?

Answer 2

It is not. Proteins are always being broken down and used, never stored. Body should always be in nitrogen balance

Question 3

Uses for amino acids

Answer 3

Make protein
Amino acids
DNA 
glucose 
Neurotransmitters
Melanin

Question 4

Name the two categories of amino acids

Answer 4

Essential (need to consume)
Non essential (conditional to bodies needs at the time)

Question 5

Which co-enzyme is very important in all reactions of amino acid metabolism? Where does it come from?

Answer 5

pyridoxal phosphate

Vitamine B6

Question 6

What can Tyrosine (phenylalanine) be metabolised to?

Answer 6

Melanine
Dopamine
Adrenaline 
Noradrenaline
thyroxine

Question 7

What can Tryptophan be metabolised to?

Answer 7

Seratonin

Melatonin

Question 8

What can Arginine be metabolised to?

Answer 8

Nitric oxide

Question 9

What can Histidine be metabolised to?

Answer 9

Histamine

Question 10

Function of the amino acids glycine, glutamate and aspartate?

Answer 10

Neurotransmitters

Question 11

What is transamination?

What catalysis it?

Answer 11

When new amino acids are made by adding side chains to the carbon skeletal of other amino acids
Enzyme- Transaminase (liver)

Question 12

What are Glucogenic amino acids? Give examaples

Answer 12

Amino acids which can be converted into glucose by gluconeogenesis and can feed into the TCA cycle as pyruvate or one of intermediates.
Alanine, glycine, tryptophan

Question 13

What are ketogenic amino acids? Give examples

Answer 13

can be converted to ketone bodies and feed TCA cycle mostly by being converted to acetyl coA or acetylacetate.
Asparate, lysine, leucine, tyrosine, glutamate

Question 14

Which amino acid is both Glucogenic and ketogenic?

Answer 14

Threonine

Question 15

How is ammonia generated?

Answer 15

During reactions which produce TCA intermediates, the amino group no longer needed given off as ammonia

Question 16

How is ammonia removed?

Answer 16

It is toxic to the body

Excreted as urea in the urea cycle

Question 17

Describe the outcomes of the metabolites of glutamate

Answer 17

1. In the muscle some of the amino acids like glutamate are converted to alanine which is exported to the liver in a process to make alpha-ketoglutarate
2. If you break down the glutamate to make glutamine you generate ammonia and some of that is send via the blood to the liver and some is sent directly to the kidney for excretion

Question 18

Glutamate and ammonia

Answer 18

. Glutamate + ammonia can be used to make glutamine in a reaction that requires ATP with a synthatase enzyme. Glutamine can be converted back to glutamate when the need arises and releases ammonia again

Question 19

Functions of glutamine and its metabolites

Answer 19

1. Important source of fuel during fasting particularly in muscles, immune cells
2. For gluconeogenesis, particularly in the kidney.
3. Produces ammonia that can acts as a buffer for protons (removed in urea)
4. As glutamate – important neurotransmitter.
5. Anti-inflammatory properties – in gut

Question 20

What are the different sources of ammonia?

Answer 20

1. Microflora in gut release ammonia when breaking down food
2. Transamination of AA (glutamine).
3. Breakdown of DNA/RNA
4. Metabolism of AA (glutamate recycling in the liver – dehydrogenase).
5. Ketogenesis/gluconeogenesis from AA releases ammonia.

Question 21

Describe main features of the urea cycle in the liver

Answer 21

Requires amino groups from aspartate and ammonia

Regulatory enzyme is CP synthase

2ATP required
Controlled allosterically by a metabolit of glutamate, N-acetyl glutamate, formed when there is an excess of glutamate so drives urea cycle.
Glutamate + acetyl-coA—- N-acetylglutamate + CoASH

Question 22

Causes of possible defects in Urea formation?

Answer 22

Regulated by 6 enzymes, defects of any of which will cause reduction in urine formation

Question 23

Symptoms of ammonia accumulation?

Answer 23

vomiting, nausea, neurological disorders, lethargy, coma.

Two types of onset – neonatal —late-onset (post-natal; 70%)

Question 24

Treatment of ammonia onset

Answer 24

Dietary management and phenylbutyrate (ammonia scavengers)