Short Answer Questions - Carbohydrates
1. What is the difference between dextrose and glucose?
A trick question: dextrose is identical to glucose
2. Is lactulose found in milk?
No, lactulose is a synthetic disaccharide used as a laxative.
3. What is the difference between inulin and insulin?
Inulin is a polymer of fructose; insulin is the hormone secreted by the ß-cells of the pancreas.
4. What are the products when amylose and amylopectin (forms of starch) are hydrolysed by amylase?
Amylose is an unbranched form of starch and is hydrolysed to form maltose only. Amylopectin is branched and forms both maltose and isomaltose.
5. Following feeding with a meal containing carbohydrate after a period of starvation, what is the first metabolic priority of the liver?
Liver glycogen is depleted during starvation. Following refeeding, the first metabolic priority is to replenish the glycogen reserves.
6. Once the first metabolic priority following refeeding (see previous question) is fulfilled, what is the principal metabolic fate of glucose delivered to the liver?
Once liver glycogen is replenished, glucose arriving at the liver is metabolised to fat (triacylglycerol).
7. Which hormone is needed for the above processes to operate?
Insulin.
8. If this hormone is absent or fails to function satisfactorily, what are the clinical consequences?
In the absence of insulin glucose accumulates in the blood, resulting in hyperglycaemia (diabetes mellitus).
9. What are the metabolic fuels available to the brain?
Glucose and the ketone bodies (ß-hydroxybutyrate and acetoacetate).
10. During starvation, following depletion of liver glycogen, what is the process by which the blood concentration of glucose is maintained (euglycaemia)?
Gluconeogenesis.
11. Under which circumstances, and by which metabolic pathway, are fatty acids metabolised to glucose?
A trick question: fatty acids cannot be metabolised to glucose.
12. Is lactulose found in milk?
No, lactulose is a synthetic disaccharide used as a laxative.
13. Name the catabolic steroid hormone that is active during starvation.
Cortisol.
14. According to the metabolic fuel hypothesis, what is the biochemical signal which triggers the secretion of insulin from pancreatic ß-cells?
ATP.
15. What disease is caused by a heterozygous inactivating mutation of glucokinase in pancreatic ß-cells?
Glucokinase maturity-onset diabetes of the young (GCK-MODY).
16. Glucose 6-phosphatase is present in both liver and muscle: true or false?
False. Glucose 6-phosphatase is present in liver where its function is to export glucose as fuel for other organs. It is not present in muscle which reserves glucose 6-phosphate for its own energy needs.
17. The insulin receptor is activated by autophosphorylation. Which disease is caused by inappropriately increased activity of protein tyrosine phosphatase?
Hyperglycaemia.
18. What is the cause of hypoglycaemia in glycogen storage disease I (von Gierke’s disease)?
Glucose 6-phosphatase deficiency in liver restricts the formation of glucose from glucose 6-phosphate.
19. Why is measurement of HbA1c used to monitor diabetes mellitus?
HbA1c provides an estimate of blood glucose concentration which is time-averaged over the 8-week period prior to testing.
20. Which drug is used as an antidote for poisoning caused by methanol and ethylene glycol?
Fomepizole, an inhibitor of alcohol dehydrogenase.
