Enzymes

Question 1

Enzymes

Answer 1

• Globular proteins that act as catalysts
• Lower the activation energy level (allows reactions to occur at lower temperatures)

Question 2

Catalysts

Answer 2

Alter the rate of a chemical reaction without undergoing permanent change themselves

Question 3

Why are enzymes effective in small amounts

Answer 3

Can be reused repeatedly

Question 4

Activation energy

Answer 4

An energy barrier that must be overcome for the reaction to take place

Question 5

Enzyme structure

Answer 5

• Have a specific 3D shape that is due to its primary structure
• Active site

Question 6

Active site

Answer 6

• A specific region of the enzyme that is functional
• Made up of a relatively small number of amino acids
• Forms a small depression within the much larger enzyme molecule

Question 7

Substrate

Answer 7

Fits neatly into the active site to form an enzyme-substrate complex

Question 8

Enzyme-substrate complex

Answer 8

The substrate molecule is held within the active site by bonds that temporarily form

Question 9

Induced fit model of enzyme action

Answer 9

• The enzyme and substrate interact
• The proximity of the substrate (a change in the environment of the enzyme) leads to a change in the enzyme that forms the functional active site
• The enzyme is flexible + can mould itself to the shape of the substrate

Question 10

How does the presence of a substrate change the shape of the active site in the induced fit model?

Answer 10

Puts a strain on the substrate molecule which distorts a particular bond in the substrate + consequently lowers the activation energy needed to break the bond

Question 11

What happens to the active site after the products are released

Answer 11

The active site reverts to its original shape

Question 12

Limitation of the lock + key model

Answer 12

It is considered as a rigid structure

Question 13

What has to occur for an enzyme to work?

Answer 13

• Come into physical contact with its substrate
• Have an active site which fits the substrate

Factors that influence the rate of enzyme activity, affect these 2 things

Question 14

How to measure an enzyme-catalysed reaction

Answer 14

• Measure its time-course (how long it takes for a particular event to run its course)
• Measure the formation of the products of the reaction (amount)
• Measure the disappearance of the substrate (concentration)

Question 15

Graph: x-axis = time, y-axis = volume of gas produced

Answer 15

Upwards curve

1. At first there is a lot of substrate and no product
2. It is very easy for substrate molecules to come into contact with empty active sites on the enzyme molecule
3. Amount of substrate starts to decrease as its broken down -> increases amount of product
4. More difficult for substrate to come into contact with enzyme due to product getting in the way
5. Takes longer for substrate to be broken down so graph becomes plateued
6. All substrate has been used up and no new product can be produced

Question 16

How to measure the rate of change on a graph

Answer 16

Gradient of tangent at a given point

Question 17

What do you have to do when investigating the effect of a certain variable

Answer 17

Keep all other variables constant

Question 18

Factors that effect enzyme action

Answer 18

• Temperature
• pH
• Enzyme concentration
• Substrate concentration

Question 19

Effect of temperature on enzyme action

Answer 19

• increases K.E. of molecules -> move around more rapidly + more frequent collisions = more successful collisions
• increasing temp. causes bonds in enzyme structure to break -> enzyme starts to change shape -> substrate fits less easily into the changed active site
• After a certain temperature, enzyme becomes denatured

Question 20

Denaturation

Answer 20

Permanent change of the enzyme that stops it from functioning altogether

Question 21

Why is human body temperature slightly lower than optimum temperature of enzymes

Answer 21

• More energy would be needed to maintain a high temp.
• Any further rise in temp. (e.g. during illness) would denature the enzymes

Question 22

What does body temperature of an organism depend on

Answer 22

Its activity

• More active organisms have a higher metabolic rate so higher temp.

Question 23

Effect of pH on enzyme action

Answer 23

• Change in pH alters the charges on the amino acids that make up the active site
• Depending on the significance of the change in pH, the bonds of the tertiary structure may break

Question 24

Effect of enzyme concentration on the rate of reaction

Answer 24

• Low enzyme concentration: Too few enzymes to allow all substrate molecules to have an active site

Intermediate enzyme concentration: All substrate molecules can occupy an active site

High enzyme concentration: The addition of further enzymes has no effect on rate of reaction (graph is plateued)

Question 25

Graph of effect of enzyme concentration on the rate of reaction

Answer 25

x-axis: enzyme conc.
y-axis: rate of reaction

Question 26

Effect of substrate concentration on the rate of enzyme concentration

Answer 26

Low substrate concentration: There are too few substrates to fill all active sites

Intermediate substrate concentration: all active sites are occupied at one time. Maximum

High substrate concentration: The addition of more substrate has no effect as all active sites are occupied at one time

Question 27

Graph of effect of substrate concentration on the rate of enzyme concentration

Answer 27

x-axis: substrate concentration
y-axis: rate of reaction

Question 28

Enzyme inhibitors

Answer 28

Directly or indirectly interfere with the functioning of the active site

Question 29

Types of enzyme inhibitors

Answer 29

• Competitive inhibitors
• Non-competitive inhibitors

Question 30

Competitive inhibitors

Answer 30

• Have a molecular shape similar to that of a substrate
• So compete with the substrate for the available active sites
• Not permanently bound

Question 31

How can the effect of a competitive inhibitor be reduced?

Answer 31

Increase substrate concentration

Question 32

Non-competitive inhibitors

Answer 32

• Attach to the enzyme on a binding site which is not the active site -> alters the shape of the enzyme and so its active site as well
• Permanently stops the enzyme from functioning