Nitrogen Metabolism

Question 1

What is creatinine and how is it used clinically?

Answer 1

Creatinine is the breakdown product of creatine and creatine phosphate in muscle
It’s used as an estimate for muscle mass and an indicator of renal function

Question 2

What is Nitrogen balance?

Answer 2

Nitrogen balance refers to the relationship between nitrogen going in and going out the body

Question 3

What are the three nitrogen balance types?

Answer 3

1) N-equilibrium (intake=output)
2) Positive N balance (intake>output)
3) Negative N balance (intake

Question 4

When is positive N balance normal?

Answer 4

Normal state for growth and pregnancy

Question 5

What is protein turnover?

Answer 5

Protein turnover refers to the continuous breakdown and re-synthesis of proteins

Question 6

Define what the term ‘Glucogenic’ and give an example

Answer 6

Amino acids that can be used for gluconeogensis e.g. valine

Question 7

Define the term ‘ketogenic’ and give an example

Answer 7

Amino acids that produce Acetyl~CoA that is used to synthesise ketone bodies e.g. Leucine

Question 8

Give an example of an amino acid that is both glucogenic and ketogenic

Answer 8

Isoleucine

Question 9

Name the hormones involved in protein reserve mobilisation under starvation and their effects

Answer 9

• Insulin & growth hormone = increase protein synthesis and decrease degradation
• glucocorticoids (e.g. cortisol) = decrease protein synthesis and increase degradation

Question 10

What is Cushing’s syndrome?

Answer 10

Th excessive breakdown of protein due to excess cortisol.

Leads to striae formation - purple stripes (typically in the abdomen)

Question 11

How are non-essential amino acids synthesised?

Answer 11

• Carbon from glycolysis intermediates, pentose phosphate pathway and kerbs cycle
• amino group from other amino acids by transamination

Question 12

Define ‘transamination’ and give the basic equation

Answer 12

Transamination is the transfer of an amino group from one molecule to another
Amino acid 1 + Keto acid 2 = Amino acid 2 + Keto acid 1

Question 13

What is the broad term used for the enzymes used in transamination?

Answer 13

Aminotransferases (transaminase)

Question 14

What does Alanine aminotransferase do?

Answer 14

Convert Alanine to Glutamate

Question 15

What does Aspartate aminotransferase do?

Answer 15

Convert Aspartate to Glutamate

Question 16

Define the term ‘deamination’ and give an example of an enzyme involved

Answer 16

Deamination is the removal of an amino group and is turned to ammonia. Uses glutaminase, glutamate dehydrogenase, amino acid oxidases

Question 17

Why is ammonia toxic?

Answer 17

Ammonia is readily diffusible
Many toxic effects e.g. alteration of blood-brain barrier, interfere with TCA cycle, pH effects, disruption of cerebral flow

Question 18

How is ammonia transported into the liver?

Answer 18

1) Glutamine = ammonia + glutamate
- transported in blood to liver where it is cleaved back to ammonia and glutamate

2) Alanine = transamination of pyruvate with glutamate
- amino group fed via glutamate into the cycle

Glutamate readily goes into urea cycle

Question 19

Give examples of diseases detected by the heel prick test

Answer 19

• Sickle dell disease
• Cystic fibrosis
• Hypothyroididm
• PKU
• Maple syrup ruin disease
• Homocystinuria

Question 20

When is the heel prick test conducted?

Answer 20

Usually after 5 days after birth

Question 21

What is Phenylketonuria (PKU)?

Answer 21

• An autosomal recessive disease that leads to the deficiency in phenylalanine hydroxylase
• Accumulation of phenylalanine and phenylketones in urine

Question 22

What does phenylalanine hydroxylase do?

Answer 22

Convert Phenylalanine to Tyrosine

Question 23

What is Tyrosine used for?

Answer 23

• Noradrenaline
• Adrenaline
• Dopamine
• Melanin
• Thyroid hormone
• Protein synthesis

Question 24

Give symptoms of PKU

Answer 24

• Severe intellectual disability
• Developmental delay
• Microcephaly
• Seizures
• Hypopigmentation

Question 25

Give treatment for PKU

Answer 25

• Low Phenylalanine diet
• High Tyrosine diet
• Avoid high protein diet

Question 26

What is homocystinuria?

Answer 26

• Autosomal recessive disease that leads to cystathionine beta-synthase
• accumulation of homocysteine and methionine

Question 27

What does cystathionine beta-synthase do?

Answer 27

Converts homocysteine to cystathionine

Question 28

Give treatments for homocytinuria

Answer 28

• Low Methionine diet
• High Cysteine diet
• vitamin B6 supplements (cofactor)