topic 8.1- metabolism

Question 1

what do metabolic pathways consist of?

Answer 1

metabolic pathways consist of chains and cycles of enzyme catalysed reactions

Question 2

give 3 common patterns of metabolism

Answer 2

• most chemical changes happen not in one large jump, but in a sequence of small steps (= metabolic pathway)
• most metabolic pathways involve a chain of reactions
• some metabolic pathways form a cycle rather than a chain

Question 3

describe the effect of enzymes on activation energy

Answer 3

enzymes lower the activation energy of the chemical reactions that they catalyse

Question 4

what is the activation energy and what does it do?

Answer 4

the activation energy is the energy required to reach the transition state, and is used to break or weaken bonds in the substrates

Question 5

describe an enzyme catalysed reaction

Answer 5

1. substrate binds to active site and is altered to reach the transition state
2. converted into the products
3. products separate from active site

the binding lowers the overall energy level of the transition state

Question 6

draw 2 diagrams for an enzyme catalysed reaction vs a non enzyme catalysed reaction

Answer 6

elsewhere

Question 7

state the 2 types of enzyme inhibitors

Answer 7

competitive and non-competitive

Question 8

what is an enzyme inhibitor?

Answer 8

a chemical substance that binds to an enzyme and reduces its activity

Question 9

describe how non-competitive enzyme inhibitors affect a reaction

Answer 9

non-competitive inhibitors bind at a location other than the active site. This results in a change of shape in the enzyme so that the enzyme cannot bind to the substrate

• the enzyme does not reach the same maximum rate because the binding of the non-competitive inhibitor prevents some of the enzymes from being able to react regardless of substrate concentration

Question 10

describe how competitive enzyme inhibitors affect a reaction

Answer 10

competitive inhibitors interfere with the active site so that the substrate cannot bind

• when the concentration of substrate begins to exceed the amount of inhibitor, the maximum rate of the uninhibited enzyme can be achieved; however, it takes a much higher concentration of substrate to achieve this max rate

Question 11

state a third type of inhibition

Answer 11

end-product inhibition

Question 12

describe end-product inhibition

Answer 12

• end product acts as an inhibitor
• binds to enzyme at allosteric site
• allosteric interaction
• functions to ensure levels of an essential product are always tightly regulated

Question 13

give and explain an example of end-product inhibition

Answer 13

pathway that converts threonine to isoleucine:
- amino acid threonine is converted to isoleucine through a series of 5 reactions
- as concentration of isoleucine builds up, it binds to the allosteric site of the first enzyme in the chain, threonine deaminase, thus acting as a non-competitive inhibitor