F212 1.3 - Enzymes

Question 1

Activation energy

Answer 1

The amount of energy needed to go from either substrate or product to the transition state i.e. the level of energy needed for the reaction to take place and which is reduced by an enzyme

Question 2

Active site

Answer 2

The region of the enzyme to which the substrate binds due to complementary shape and charge distributions

Question 3

Allosteric activator

Answer 3

A substance binding to an allosteric site and activating the enzyme

Question 4

Allosteric inhibitor

Answer 4

A substance binding to an allosteric site and inhibiting the enzyme

Question 5

Allosteric site

Answer 5

A site spatially distinct from the active site to which a molecule binds influencing the shape of the enzyme, including the active site

Question 6

Catalyst

Answer 6

Something which changes the rate of a reaction (usually speeds it up) but is itself unchanged at the end of the reaction

Question 7

Coenzyme

Answer 7

An organic non-protein molecule that binds to the enzyme at the same time as the substrate and is essential for catalysis to proceed during the course of which the coenzyme is modified and released in a different form. Important coenzymes are NAD, NADP and FAD

Question 8

Cofactor

Answer 8

A molecule or ion which helps an enzyme to work. It can be a coenzyme or an inorganic ion

Question 9

Competitive inhibitor

Answer 9

A substance able to reduce the rate of an enzyme-catalysed reaction by binding at the active site usually because of a close structural and charge distribution to those of the normal substrate

Question 10

End-product inhibition

Answer 10

The end-product of a metabolic pathway acting to inhibit the pathway, usually by reversibly inhibiting one of the enzymes at the beginning of the pathway. An example of negative feedback

Question 11

Enzyme

Answer 11

A protein that acts as a biological catalyst by lowering the activation energy needed to achieve the transition state.

Question 12

Enzyme-substrate complex:

Answer 12

The intermediate structure formed by substrate binding to enzyme that develops into the transition state which then becomes the enzyme product complex

Question 13

Extracellular enzyme

Answer 13

An enzyme made in the cell then secreted to act outside of the cell

Question 14

Induced fit hypothesis

Answer 14

A modern theory relating to enzyme catalysis which suggests that both enzyme and substrate (or either) undergoes a conformational change on forming the enzyme-substrate complex improving the complementary fit between them and making catalysis more probable

Question 15

Intracellular enzyme

Answer 15

An enzyme which acts inside the cell

Question 16

Irreversible inhibitor

Answer 16

An inhibitor which attaches permanently to an enzyme

Question 17

Optimum

Answer 17

The best or most favourable condition. Each enzyme has an optimum pH

Question 18

Lock-and-key hypothesis

Answer 18

An old theory relating to enzyme catalysis which drew an analogy between the enzyme and a lock and its substrate as the only key that would fit thereby explaining the specific nature of enzyme catalysis

Question 19

Maximum velocity

Answer 19

The greatest rate of catalysis possible by an enzyme achieved only when the substrate concentration is high enough to keep the active site reloaded with a fresh molecule as fast as product is released

Question 20

Non-competitive inhibitor

Answer 20

A substance able to reduce the rate of an enzyme-catalysed reaction by binding to a site other than the active site and interfering with the catalytic mechanism

Question 21

Product

Answer 21

The substance made in an enzyme-catalysed reaction from the substrate and released from the active site

Question 22

Reversible inhibitor

Answer 22

An inhibitor which attaches temporarily to an enzyme

Question 23

Substrate

Answer 23

The substance used up in an enzyme-catalysed reaction and converted to product after binding to the active site

Question 24

Transition state

Answer 24

A very high energy, very unstable molecular structure in between substrate and product found only very briefly and only in the active site as the two interconvert