Energy Storage - Protein

Question 0

What happens during stage 1 of the catabolism of proteins?

Answer 0

Proteases and peptidases hydrolyse peptide bonds to release free amino acids. They are then absorbed into the circulation.

Question 1

Where does stage 1 of the catabolism of protein occur?

Answer 1

In the GI tract

Question 2

What can the amino acids be used for?

Answer 2

Protein synthesis

Synthesis of N containing compounds

Question 3

What does it mean if an amino acid is ketogenic?

Answer 3

Once the amine group is removed, it’s C skeleton can be converted to acetyl CoA which can go onto make ketone bodies

Question 4

What does stage 2 catabolism of amino acids produce?

Answer 4

Acetyl CoA
Oxaloacetate
Alpha-ketoglutarate
Fumarate
Succinate

Question 5

How much nitrogen is in the body of a 70kg man?

Answer 5

2kg

Question 6

What does nitrogen leave the body as?

Answer 6

Urea, ammonia, creatinine, uric acid, urine.

Also lost in skin and hair.

Question 7

When would someone have a positive N balance?

Answer 7

Growth, tissue repair, pregnancy, convalescence

Question 8

When is there a negative N balance?

Answer 8

Starvation, trauma, malnutrition

Question 9

List the 8 essential amino acids

Answer 9

Lysine, isoleucine, leucine, threonine, valine, tryptophan, phenylalanine, methionine

Question 10

What happens to the excess amino acids?

Answer 10

Converted to intermediates of carbohydrate and lipid metabolism or oxidised to produce energy

Question 11

What is the major site of the breakdown of amino acids?

Answer 11

The liver

Question 12

What are the three common features of amino acid catabolism?

Answer 12

C atoms converted to intermediates of carbohydrate and lipid metabolism
Usually start with the removal of the amine group (transamination/deamination)
N atoms converted to urea

Question 13

What stimulates transaminases?

Answer 13

Cortisol

Question 14

Which two transaminases are clinically important and why?

Answer 14

Alanine aminotransferase (ALT/GPT)
Aspartate aminotransferase (AST/GOT)

Measured in serum to assess liver function

Question 15

Which enzyme is normally deficient in phenylketonuria and and what does it normally do?

Answer 15

Phenylalanine hydroxylase

Oxidises phenylalanine to tyrosine

Question 16

In PKU, what happens to phenylalanine when it accumulates in tissues? What effect does this have?

Answer 16

Metabolised to phenylpyruvate
It inhibits pyruvate uptake by mitochondria and interferes with energy metabolism in the brain.
-> inhibition of brain development

Question 17

How is PKU diagnosed?

Answer 17

Detection of phenylketones in urine or measurement of blood phenylalanine concentration (normally less than 0.1mmol/L but can exceed 1mmol/L in PKU)

Question 18

What type of inheritance is homocystinuria?

Answer 18

Autosomal recessive

Question 19

What is the deficient enzyme in homocystinuria and what does it normally do?

Answer 19

CBS

Normally converts homocysteine to cystathionine. This is further converted to cysteine.

Question 20

What happens in homocystinuria?

Answer 20

Deficient CBS enzyme so homocysteine levels increase in the blood. Some is converted to methionine so this is increased. Homocystine (oxidised form) can be found in the urine.

Question 21

What does homocystinuria cause?

Answer 21

Disorders of connective tissue, muscle, CNS and cardiovascular system. Can therefore be confused with Marfan’s syndrome in children.

Question 22

What is hyperammonaemia associated with?

Answer 22

Blurred vision, tremors, slurred speech, coma, death

Question 23

How does ammonia get into the body?

Answer 23

Produced by many tissues and can be absorbed from the gut

Question 24

What enzyme converts ammonia to glutamine and what else is needed?

Answer 24

Glutamine synthetase

Glutamate and ATP

Question 25

What does glutaminase do?

Answer 25

Hydrolyses glutamine to ammonia and glutamate in the kidneys

Question 26

How is the urea cycle regulated?

Answer 26

Enzymes are inducible.
High protein diet induces enzymes.
Low protein diet represses enzymes.

Question 27

What does a deficient enzyme in the urea cycle cause?

Answer 27

Complete loss
-fatal

Partial loss

• hyperammonaemia
• accumulation/excretion of a urea cycle intermediate

Question 28

Symptoms of a deficiency in an enzyme of the urea cycle?

Answer 28

Irritability, vomiting, lethargy

Seizures, coma, death

Question 29

How is a deficiency in one of the enzymes of the urea cycle treated?

Answer 29

Low protein diet

Question 30

How is ammonia thought to be toxic?

Answer 30

Removes alpha-ketoglutarate from the TCA cycle.

Reacts with it to form glutamate via the enzyme glutamate dehydrogenase