BCH3702 MEMO SEMESTER 2 2015
ASSIGNMENT 01
Due date: 21 August 2015
Your unique number is: 594176
Answer all questions
Question 1
Give a thorough explanation of the events that are likely to happen if a key enzyme
in a metabolic pathway is inhibited or is deficient [10]
• The major effects of key enzyme deficiency include amongst others
accumulation of substrate on which the enzyme act a d a decrease in the
metabolic by-products of the substrate which may have profound
physiologic/metabolic consequences.
• Blockage of all downstream reactions occurs, resulting in failure of the
pathway to complete. i.e. an enzyme deficiency causes a deficiency in
products of the reaction it catalyses, which will subsequently inhibit other
reactions that depends on the availability of those products.
• Build-up of substrate and lack of by-product may manifest as metabolic
disorders. Moreover, the accumulation of substrate might be toxic
• In the event where other enzyme(s) [from other pathways] act on the
same substrate, the deficiency of the enzyme may be minor. Similarly, in
the event where the substrate is a precursor in another metabolic
pathway, the effects may be minor. i.e., if the accumulated substrate can
leak out into other pathways to be used up).
Question 2
Explain the increase in blood concentrations of pyruvate, lactate and alanine in
individuals with pyruvate dehydrogenase complex deficiency [5]
Pyruvate dehydrogenase complex is important in the conversion of pyruvate to acetyl-COA. In
the absence of pyruvate dehydrogenase complex, pyruvate will accumulate. Pyruvate is then
reduced to lactate. More pyruvate is also transaminated to alanine. This is why a deficiency in
pyruvate dehydrogenase complex results in a high level of pyruvate, lactate and alanine in the
blood.
Question 3
Type II diabetes mellitus is managed by inhibitors of enzymes that digest
carbohydrates in the intestines.
i. Give a description type II diabetes mellitus. [5]
Briefly, diabetes mellitus is a disease characterized by inability of cells to absorb glucose
from the blood, with the result that blood glucose concentration remains high
ii. Suggest a mechanism for the drugs. [5]
Enzyme inhibitors inhibit the digestion of polysaccharides in the gastrointestinal tract,
retarding absorption of monosaccharides and disaccharides by the intestinal mucosal
cells. This has an effect of reducing post-prandial hyperglycaemia.
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