8.1 Enzyme Inhibition

Question 1

What are competitive inhibitors?

Answer 1

• chemicals that bind to the active site
• prevent the substrate from combining with the enzyme (slowing reaction rate)
• substrate and inhibitor are chemically similar
• if the amount of substrate is increased then there will eventually be more substrate collisions than inhibitor collisions
  graph: lines meet eventually, inhibitor line is a straight line until eventually levels off

Question 2

Examples of competitive inhibitors

Answer 2

• many antibiotics are competitive inhibitors of growth factors that are needed in bacterial metabolism
• malonate is a poison that is structurally similar to the substrate succinate which is found in the Krebs Cycle
• it binds to the active site of dehydrogenase enzyme
• hence process of respiration stops and cell death occurs

Question 3

What are non-competitive inhibitors?

Answer 3

• do not bind to active site
  not chemically similar to substrate
• bind to a different site on enzyme and change the shape of the active site
  the substrate may still be able to bind to the active site however enzyme is not able to catalyse reaction or can only do it at a slower rate
• allosteric inhibition is non-competitive
  graph: as substrate conc increased the line with non-comp inhibitor increases with same shape but lines run parallel to each other and never meet

Question 4

Examples of non-competitive inhibition

Answer 4

arsenic

• inhibits the functioning of pyruvate dehydrogenase
• results in disruption of the energy system in cells and they die

Question 5

What are metabolic pathways?

Answer 5

• consist of chains and cycles of enzyme-catalysed reactions
• are complex with many small reactions making intermediate compounds each controlled by their own enzyme
• if an enzyme is blocked halfway through the metabolic pathway then you are unable to receive later enzymes needed

Question 6

What is end-product inhibition?

Answer 6

• a form of negative feedback in which increased levels of a product decrease the rate of product formation
• because metabolic pathways usually consist of chains or cycles the product can regulate the rate of its own production by inhibiting an earlier enzyme in the pathway
• the product binds to an allosteric site causing conformational change to the active site
• as enzyme cannot function the rate of product formation will decrease

Question 7

Example of end product inhibition

Answer 7

the pathway that converts threonine to isoleucine
- the product isoleucine becomes an non-competitive inhibitor to the enzyme that catalyses the first reaction (threonine deaminase)