The following exercises are available in this section
Sugars, starches and the glycaemic index
By the end of this exercise you should be able to:
- Explain what is meant by the term glycaemic index and describe in outline how it is measured
- Describe the main types of carbohydrate and explain how carbohydrates can be classified on the basis of their chemistry
- Explain the processes involved in the digestion and absorption of carbohydrates
- Describe the structure of starch and explain how starch may be rapidly or slowly digested, or may be more or less completely resistant to digestion
- Describe the fates of undigested starch and non-starch polysaccharides
- Explain the beneficial effects of resistant starch and non-starch polysaccharides in the diet
Bloating, flatulence and diarrhoea after drinking milk - but not yoghurt or cheese
By the end of this exercise you should be able to:
- Explain why most people (other than those of north European origin) have some degree of lactose intolerance and suffer gastrointestinal discomfort after consuming milk, but are able to consume yogurt and cheese with no problems.
- Describe in outline the anaerobic metabolism of glucose in yeast, leading to the formation of ethanol and carbon dioxide.
- Describe the inhibition of glucose metabolism in bacteria and red blood cells by fluoride.
- Describe the way in which glucose metabolism in red blood cells is linked to the formation of ATP, and is controlled by the availability of ADP and inorganic phosphate.
Experiments on glucose metabolism
By the end of this exercise you should be able to:
- Explain the importance of ADP, NAD and inorganic phosphate in the metablism of glucose.
- Explain how the metabolism of 1 mol of glucose leads to the formation of 2 mol of lactate and 2 mol of ATP.
- Describe the pathway of glycolysis and explain how it is possible to maintain anaerobic glycolysis in muscle and red blood cells.
Life-threatening acidosis in an alcoholic - and in a hunger striker given intravenous glucose
By the end of this exercise you should be able to:
- Explain how thiamin deficiency leads to (potentially life-threatening) acidosis with elevated plasma concentrations of lactate and pyruvate
- Describe the reactions catalysed by the pyruvate dehydrogenase multi-enzyme complex and the role of thiamin diphosphate
- Describe a simple functional test of thiamin nutritional status
Breathless after sprinting
By the end of this exercise you should be able to:
- Explain why lactate is produced by muscle under conditions of maximum exertion
- Describe the pathway of gluconeogenesis from lactate
- Explain what is meant by the term oxygen debt
Weight loss in a patient with advanced cancer
By the end of this exercise you should be able to:
- Calculate a person's energy deficit from his / her weight loss
- Calculate a person's BMR from resting oxygen consumption
- Explain why BMR is elevated in cancer cachexia and explain what is meant by the term hypermetabolism
- Describe the energy-expensive metabolic cycling between anaerobic glycolysis in the tumour and gluconeogenesis in the liver
How is NADH from glycolysis normally re-oxidised?
By the end of this exercise you should be able to:
- Describe the malate-aspartate shuttle for transfer of reducing equivalents from the cytosol into mitochondria
- Describe the glycerol phosphate shuttle for transfer of reducing equivalents from the cytosol into mitochondria
- Explain why the glycerol phosphate shuttle is less energetically efficient than the malate-aspartate shuttle, but is important in tissues with a high rate of glycolysis
An adverse response to antimalarial medication - and a fatal reaction to fava beans
By the end of this exercise you should be able to:
- Describe the pentose phosphate pathways and explain its importance as a source of NADPH and pentose sugars
- Explain the role of glutathione in protection against oxidative damage and how impaired activity of glucose 6-phosphate dehydrogenase leads to haemolysis
- Explain why only males are normally affected by an X-linked recessive genetic disease
Fasting hypoglycaemia in an infant - and poor exercise tolerance in two brothers
By the end of this exercise you should be able to:
- Describe the steps involved in the synthesis and utilisation of glucose 1-4 links in glycogen
- Explain the importance of liver glycogen synthesis in controlling the plasma concentration of glucose in both the fed and fasting states
- Explain the importance of muscle glycogen for muscle metabolism in intense exercise
- Explain the importance of branching in glycogen
- Describe the steps involved in the formation of branch points in glycogen
Alanine released from muscle in fasting
By the end of this exercise you should be able to:
- Explain how muscle glycogen can provide an indirect source of blood glucose in the fasting state
- Describe the way in which alanine can act as a substrate for gluconeogenesis in the liver, by undergoing transamination to pyruvate
- Describe the way in which muscle glycogen can undergo glycolysis to pyruvate and transamination to alanine, which is exported to the liver
A hypoglycaemic adolescent with an enlarged liver and gout
By the end of this exercise you should be able to:
- Distinguish between different possible ways in which enzyme or hormone receptor defects may lead to excessive accumulation of glycogen in the liver, and fasting hypoglycaemia.
- Explain how lack of glucose 6-phosphatase leads to excessive accumulation of glycogen in the liver and profound hypoglycaemia on fasting.
- Explain how lack of glucose 6-phosphatase leads to lactic acidosis in the fasting state, and how this may lead to the development of gout.
Two diabetic patients in coma
By the end of this exercise you should be able to:
- Explain how both hypoglycaemia and hyperglycaemia can cause coma
- Explain the effects of excessive injection or secretion of insulin
- Explain the consequences of not injecting insulin in a person with type I diabetes mellitus
- Describe the differences between type I and type II diabetes mellitus, and explain why hyperglycaemia with keto-acidosis is rare in people with type II diabetes.
- Explain why total pancreatectomy is not a realistic option for treatment of a patient with cancer of the pancreas.
Was she murdered by insulin injection?
By the end of this exercise you should be able to:
- Explain how excessive insulin or consumption of alcohol and a small amount of carbohydrate can cause hypoglycaemia
- Describe in outline what is involved in biological assay and radio-immunoassay of insulin
- Explain why insulin is measure in units of biological activity and why insulin syringes are calibrated in units
- Describe the processes involved in the synthesis of insulin
- Explain the importance of the C-peptide in clinical chemistry
An unusual cause of diabetes - how the pancreas senses a rise in blood glucose
By the end of this exercise you should be able to:
- Explain what is meant by isoenzymes
- Explain how the Km of an enzyme, relative to the concentration of the substrate, affects the rate of reaction
- Explain the importance of glucokinase in the liver
- Explain how the pancreas senses an increased concentration of glucose in the portal blood, and how this acts as a signal for secretion of insulin.