Topic 1.4 Enzymes

Question 1

What is an enzyme?

Answer 1

a biological catalyst (globular proteins)

Question 2

What is a catalyst?

Answer 2

a substance that speeds up the rate of a reaction without changing the substances being produced or being changed itself

Question 3

What is an enzyme (long definition)?

Answer 3

proteins that have a very specific shape due to their primary, secondary, tertiary and quaternary structures. they act as biological catalyst and each enzyme will only catalyse a certain reaction

Question 4

Enzymes show specificity, what is meant by this?

Answer 4

the characteristic of enzymes which means due to their very specific shapes as a result of their tertiary and quaternary, each enzyme only catalyses a specific reaction or group of reactions

Question 5

What’s an anabolic reaction?

Answer 5

a reaction which builds up new molecules (synthesises) in a cell

Question 6

What’s a catabolic reaction?

Answer 6

a reaction that breaks down substances within a cell

Question 7

Describe what is meant by metabolism

Answer 7

the sum of anabolic and catabolic processes in a cell

Question 8

What is a metabolic chain/pathway?

Answer 8

a series of linked reactions in the metabolism of a cell

Question 9

Define intracellular and extracellular enzymes

Answer 9

intracellular catalyse reactions within the cell e.g. DNA polymerase
extracellular catalyse reactions outside of the cell in which they were made e.g. lysozyme

Question 10

Define activation energy

Answer 10

the energy needed for a reaction to get started

Question 11

What is a substrate?

Answer 11

the molecule or molecules on which the enzyme acts

Question 12

What is the lock-and-key hypothesis?

Answer 12

the model that explains enzyme action by an active site in the protein structure that has avert specific shape. the enzyme and substrate slot together to form a complex as a key fits in a lock

Question 13

What’s an active site?

Answer 13

the area of an enzyme that has a specific shape into which the substrate of a reactions fits

Question 14

Describe the induced-fit hypothesis

Answer 14

a modified version of the lock-and-key theory where the active site is considered to have a more flexible shape. once the substrate enters the active site, the shape of the site is modified around it to form the active complex. once the products have left the active site it reverts to its inactive, relaxed form

Question 15

What is the initial rate of reaction?

Answer 15

the measure taken to compare the rates of enzyme controlled reactions under different conditions

Question 16

What is meant by molecular activity/ turnover number?

Answer 16

the number of substrate molecules transformed per minute by a single enzyme molecule

Question 17

What is the temperature coefficient (Q10)?

Answer 17

the measure of the effect temperature has on the rate of reaction

Question 18

What happens to Q10 between 10 degrees and 40 degrees?

Answer 18

it doubles for every 10 degree temperature rise

Question 19

Give 3 examples of enzyme inhibition

Answer 19

• competitive
• non-competitive
• end-product

Question 20

Give an example of a chemical that exerts irreversible inhibition on enzyme systems

Answer 20

cyanide, arsenic and mecury

Question 21

Define enzyme inhibitors

Answer 21

substances that slow down enzymes or stop them from working

Question 22

What is reversible inhibition?

Answer 22

inhibition of the action of an enzyme by an inhibitor which does not permanently affect the functioning of an enzyme and can be removed from the enzyme

Question 23

What is reversible inhibition often used for?

Answer 23

to control the reaction rates within a cell

Question 24

What is irreversible inhibition?

Answer 24

inhibition of the action of an enzyme that is permanent and cannot be undone (never used within cells to control the rates of reaction)

Question 25

Define competitive inhibition

Answer 25

inhibition in which the inhibitor molecule is similar shape to the substrate molecule and competes with it for the active site of enzymes

Question 26

Define non-competitive inhibition

Answer 26

inhibition in which the inhibitor doesn’t compete for the active site but forms a complex with the enzyme or enzyme/substrate complex and changes the shape of the active site so it can no longer catalyse the reaction

Question 27

Define regulatory enzymes

Answer 27

enzymes that have a site separate to the active site where another molecule can bind to have either an activating or inhibitory affect

Question 28

Define end-product inhibition

Answer 28

a control system in many metabolic pathways in which the enzyme at the beginning of the pathway is inhibited by one of the end products of the reaction