L17: Nitrogen Metabolism

Question 2

What is the amino acid pool?

Answer 2

Collection of free amino acids at low concs inside cells/blood stream. It includes mixing & exchange with other free amino acids around the body.

Question 3

Why is protein needed in a diet?

Answer 3

No ‘storage’ form of protein in the body to replace amino acids & other N containing compounds.

Replace lost amino acids & allow tissue repair

Question 4

Positive & negative nitrogen balance in terms of N intake & N excretion

Answer 4

Positive: N intake > N excretion
Negative: N intake < N excretion

Question 5

Causes of positive nitrogen balance

Answer 5

1) Pregnancy
2) After immobilisation after accident
3) Recovering from serious illness
4) During normal growth in children

Question 6

Causes of negative nitrogen balance

Answer 6

1) During illness
2) Starvation
3) Late stages of some cancer
4) Injury/trauma

Question 7

Most cellular proteins degradation pathways

Answer 7

• Recognised as ‘old’ or damaged
• Removed by ubiquitin breakdown system
• Mixture of 20 amino acids

Question 8

Foreign ‘exogenous’ proteins degradation pathways

Answer 8

• ‘Old’ or damaged sub-cellular organelles
• Taken into vesicles by endocytosis where vesicles fuse with lysosomes & proteolytic enzymes degrade proteins into amino acids

Question 9

Define deamination

Answer 9

Removal of alpha-amino group

Question 10

Where does deamination occur?

Answer 10

Liver mitochondrial matrix

Question 11

What is deamination in this reaction
Glutamate -> a-Ketoglutarate + NH4+
catalysed by?

Answer 11

Glutamate dehydrogenase

Question 12

Why does deamination remove the amino group from glutamate?

Answer 12

It can enter the Urea cycle for safe disposal

Question 13

Define transamination

Answer 13

Conversion of 1 amino acid to another

Question 14

Process of transamination

Answer 14

a-amino group is transferred from an amino acid to a-ketoglutarate to produce glutamate + a keto acid

Question 15

Whhat is transamination catalysed by?

Answer 15

Aminotransferases/transaminases

Question 16

What is
alanine + a-KG -> glutamate + pyruvate
catalysed by?

Answer 16

alanine aminotransferase

Question 17

What is
aspartate + a-KG -> glutamate + oxaloacetate
catalysed by?

Answer 17

aspartate aminotransferase

Question 18

Define transdeamination

Answer 18

Combined action of aminotransferases & glutamate to allow a-amino groups to enter Urea cycle

Transamination & deamination

Question 19

Role of glutamine

Answer 19

Transport of ammonia in the blood

Question 20

How many N in glutamate & glutamine?

Answer 20

Glutamate: 1N
Glutamine: 2N

Question 21

What does the glucose-alanie cycle allow the liver to do?

Answer 21

Regenerate glucose from this alanine

Question 22

Where and when is alanine generated?

Answer 22

Generated in skeletal muscle during exercise

Question 23

What happens to glutamine that transports ammonia to liver?

Answer 23

Glutamine converted to glutamate + ammonia

Question 24

What is alanie converted to from skeletal muscle?

Answer 24

Glutamate + Pyruvate

Question 25

What is glutamate deaminated to generate?

Answer 25

a-ketoglutarate & ammonia

Question 26

Which carbon skeletons can enter TCA cycle to generate ATP?

Answer 26

Pyruvate Oxaloacetate Fumarate Succinul-CoA a-Ketoglutarate

Question 27

Which carbon skeletons can produce ketone bodies?

Answer 27

Acetoacetyl-CoA & Acetyl-CoA

Question 28

Define essential amino acids

Answer 28

Cannot be synthesised in humans- must be obtained via diet

Question 29

Role of glutamate

Answer 29

Central to amino acid degration

Question 30

Role of glutamine

Answer 30

Transport ammonia to the liver

Question 31

Role of alanine

Answer 31

Transport ammonia from skeletal muscle to the liver