Carbohydrate Metabolism

Question 1

Hereditary fructose intolerance

Answer 1

Deficiency in fructose-1-phosphate aldolase –> prevents cleavage of fructose-1-phosphate to DHAP and GAP
Characterised by hypoglycaemia after fructose ingestion, death in young children after prolonged ingestion
F-1-P accumulates intracellularly –> deplete cells of free Pi and reduce ability to make ATP

Question 2

PDH deficiency

Answer 2

Severe neurological defects
Childhood death
Raised blood levels of lactate, pyruvate, alanine –> acidosis

Question 3

Alcoholism

Answer 3

Reduction in thiamine (vitamin B1) absorption from diet
Reduction in thiamine phosphorylation to thiamine pyrophosphate (TPP) in liver
TPP cofactor for PDH
Reduction in PDH activity –> mental disorder

Question 4

McArdles disease

Answer 4

Absense of muscle glycogen phosphorylase
Limit strenuous exercise –> painful muscle cramps
Failure to utilise stores of glycogen to make ATP

Question 5

Gierke’s disease

Answer 5

Failure to break down G-6-P during hypoglycaemia leads to inappropriate production of glycogen (stimulated by rise in G-6-P)

Question 6

Defiency in glucose-6-phosphate dehydrogenase

Answer 6

Reduces NADPH availability
Increase oxidative stress –> problem due to lack of reduced GSH
Symptoms: black urine, jaundice, haemolytic anaemia

Question 7

Galactosemia

Answer 7

Rare inherited inability to metabolise galactose
Mild form:when galactokinase deficient
Severe form: when galactose-1-phosphate uridyl transferase absent –> high blood and urine levels of galactose
Symptoms:
Failure to thrive
Vomiting and diarrhoea after birth
Enlargement of liver and jaundice and even cirrhosis
Cataracts
Lethargy
Mental retardation