enzymes basics

Question 1

define ‘enzyme’

Answer 1

a biological catalyst which increases rate of reaction
- globular proteins

Question 2

how do enzymes increase rate of reaction?

Answer 2

provides an alternate reaction pathway with a lower activation energy

Question 3

describe the active site of an enzyme

Answer 3

• binds to complementary substrate
• specific shape

Question 4

describe the lock and key mechanism

Answer 4

enzyme = lock
substrate = key
must collide perfectly
- The products of the reaction are then released and it is now an enzyme-product complex

Question 5

describe the induced fit mechanism

Answer 5

active site changes shape slightly to fit the substrate forming an enzyme substrate complex
- R groups in the active site interact with the substrate to form temporary bonds
- there is a change in tertiary structure
- strain is put on the substrate bonds and they are weakened

Question 6

why is the induced fit mechanism better?

Answer 6

it is more likely that the active site will change slightly when there are frequent fast collisions, rather than a perfect collision

Question 7

what is an intracellular enzyme?

Answer 7

enzymes that act within cells

Question 8

what is an extracellular enzyme?

Answer 8

enzymes released from cells to break down nutrients

Question 9

what is an anabolic reaction?

Answer 9

built up
- growth, synthesis

Question 10

what is a catabolic reaction?

Answer 10

break down

Question 11

what is an example of an intracellular enzyme?

Answer 11

catalase

Question 12

how do enzymes affect structure?

Answer 12

they are involved in collagen production

Question 13

how do enzymes affect function?

Answer 13

processes such as respiration or photosynthesis

Question 14

Why must enzymes be in an aqueous environment?

Answer 14

It allows both the enzyme and the substrate the ability to move and therefore collide with one another allowing for enzyme-substrate complexes

Question 15

What is the structure of an enzyme?

Answer 15

• Globular protein: has a 3D, spherical shape + water soluble due to positioning of hydrophilic R group
• Has an active site: which has a very specific shape where the complementary substrate binds to

Question 16

What effect does an increase in temperature (from 10 to 30 c) have on the rate of a reaction?

Answer 16

Kinetic energy is increased which increases the number of successful collisions, therefore more enzyme-substrate complexes are formed and the rate of reaction increases

Question 17

What is meant by optimum temperature?

Answer 17

When enzyme activity is at its highest

Question 18

What happens when the temperature is raised too high (40 to 60 c) on the rate of a reaction?

Answer 18

• increase of energy means vibrations are produced which break the bonds that hold the enzyme together
• the enzyme denatures, meaning there is now an irreversible change to the shape of the active site, and so enzyme activity and rate of reaction decreases

Question 19

What does the temperature coefficient show in a reaction?

Answer 19

It shows how much the rate of the reaction changes when the temperature is raised by 10 degrees

Question 20

What is the formula for the temperature coefficient?

Answer 20

Q10 = rate at higher temperature / rate at lower temperature

Question 21

What is meant by optimum pH?

Answer 21

The pH the enzyme works best at

Question 22

What happens as you move away from the optimum pH on a graph?

Answer 22

The enzyme begins to denature (the H+ and OH- ions found in acids and alkalis break the ionic and hydrogen bonds that hold the enzymes tertiary structure together, resulting in it changing shape. Therefore enzyme activity decreases.

Question 23

Explain the effect of having few substrate molecules on rate of reaction.

Answer 23

Few substrate molecules mean there are many active sites free and able to be reacted, and so an increase in substrate concentration will increase the rate of reaction

Question 24

Explain the effect of having more substrate molecules on rate of reaction.

Answer 24

When there are more substrate molecules, all the active sites are engaged in catalysts. This therefore produces the maximum rate of reaction

Question 25

Explain the effect of having an excess of substrate molecules on rate of reaction.

Answer 25

An excess of substrate molecules means all active sites are engaged in catalysis and so an increase in substrate concentration will not change the rate of reaction

Question 26

what is meant by ‘enzyme specificity’?

Answer 26

enzymes only fit with a complementary substrate which has the exact shape to fit the active site

Question 27

how will the substrate changing shape slightly assist enzyme action

Answer 27

it puts a strain on the bonds and they can break more easily

Question 28

how do small molecules join to form polysaccharides? (3 marks)

Answer 28

• peptide bonds
• condensation reaction
• water removed

Question 29

why does the structure of an enzyme molecule allow them to be detected in solution using the biuret test? ( 1 mark)

Answer 29

enzymes are globular and water soluble