1.4 Enzymes

Question 1

Why do enzymes only catalyse one reaction?

Answer 1

The active site of the enzyme has a specific shape

The substrate has a complementary shape and therefore binds into the active site

Question 2

How does a competitive inhibitor work?

Answer 2

It has a similar shape to the substrate
It had a complementary shape to the active site
It binds to the active site
When it does bind it prevents the substrate from doing so
Fewer enzyme-substrate complexes formed

Question 3

Describe and explain the effect of temperature on the rate of activity of an enzyme

Answer 3

• increase in rate along with increase in temperature up to optimum due to increased kinetic energy so molecules move faster and more successful collisions/ more enzyme-substrate complexes formed
• at temperatures above optimum there are increased vibrations which cause the Hydrogen bonds to break and the tertiary structure changes and a change of shape of the active site and the enzyme is DENATURED

Question 4

Factors affecting enzyme activity (5)

Answer 4

Inhibitors
Temperature 
pH
Concentration of substrate 
Concentration of enzyme

Question 5

Distinguish between intracellular and extracellular enzymes

Answer 5

Intra - work inside the cell

Extra - work outside the cell

Question 6

Advantages of immobilised enzymes

Answer 6

• greater stability over a wider range of temperature and pH
• products are easily recovered
• products aren’t contaminated with the enzyme
• enzymes are easily added or removed
• more than 1 enzyme may be used
• enzymes can be reused

Question 7

Enzymes are biological catalysts. What does this mean?

Answer 7

Biological - produced by cells and is a protein

Catalyst - speed up rate of reaction without being used up

Question 8

What is metabolism

Answer 8

Series of enzyme-controlled reactions in the body

Question 9

Anabolic reactions

Answer 9

Building up molecules
Requires ATP
Eg protein synthesis

Question 10

Catabolic reaction

Answer 10

Breaking down molecules
Releases energy
Eg digestion of proteins

Question 11

Key point about enzymes

Answer 11

• speed up chemical reactions
• lower the activation energy
• dont take part in the reaction
• needed in small quantities
• can be reused
• convert substrates into products
• biological catalysts

Question 12

Describe the structure of enzymes

Answer 12

• tertiary structure that is held by Hydrogen, ionic and disulphide bonds
• creates an active site where substrate can bind
• act in aqueous environments as they’re soluble and can catalyse hydrolysis

Question 13

Intracellular

Answer 13

Work inside the cell

Question 14

Extracellular

Answer 14

Work outside the cell

Question 15

What is an enzyme-substrate complex

Answer 15

Temporary complex when an enzyme binds to a substrate such that the substrates are close enough to react

Question 16

What is the active site

Answer 16

Small region on the enzyme where the substrate binds

Question 17

Lock and key model

Answer 17

• substrate has a complementary shape to the enzyme’s active site
• explains enzyme specificity

Question 18

Induced fit theory

Answer 18

• suggests the active site of enzyme may not exactly correspond to the substrate
• enzyme’s shape alters slightly to accommodate substrate
• enzyme will revert back to ‘relaxed’ state after the products are formed and repelled
• suggests enzyme is flexible and not rigid

Question 19

How do enzymes work

Answer 19

Lowering the activation energy needed to make chemical reactions to start

Question 20

Factors affect the rate of enzyme action

Answer 20

• substrate concentration
• temperature
• pH
• enzyme concentration
• presence of inhibitors

Question 21

What is inactivation

Answer 21

Reversible reduction of enzyme activity at low temperature as molecules have insufficient kinetic energy to from enzyme-substrate complexes

Question 22

What is denatured

Answer 22

Permanent changes to the shape of the active site which prevents the substrate from binding

Question 23

Describe the effect of substrate concentration on enzyme activity

Answer 23

Low concentration = low rate
• limits chance of successful collisions 
• is a limiting factor
High concentration = high rate
• greater chance of successful collisions resulting in more enzyme-substrate complexes
Plateau = highest rate
• enzyme active sites are saturated 
• no longer a limiting factor

Question 24

Describe effect of temperature on enzyme activity

Answer 24

Low temperature = low rate
• enzyme is inactivated
• insufficient kinetic energy so few successful collisions
Increase in temperature up to optimum = increase in rate
• increase in KE
•increases chance of successful collisions so more enzyme-substrate complexes
Temperature above optimum = rapid decrease
• hydrogen bonds break due to increased vibrations
• shape of active site changes and enzyme is denatured
• no successful collisions

Question 25

Describe the effect of pH on enzyme activity

Answer 25

pH increases or decreases either side of the optimum = decreases rate • charges on R group on AA on active site are influenced by H+ and OH- • if too many H+ or OH- the substrate can be repelled from the active site which stops it from binding • small changes - reversible • excessive changes - ionic bonds break which denatures the enzyme

Question 26

Look

Question 27

Look

Question 28

Look

Question 29

What is a limiting factor

Answer 29

Increase in it's value causes an increase in the rate of reaction

Question 30

Describe affect of enzyme concentration on enzyme activity

Answer 30

* as they can be reused only a low concentration is needed to catalyse a large number of reactions * as long as the temperature and pH are suitable and there's an excess of substrate then the rate will be directly proportional to the enzyme concentration

Question 31

Look

Question 32

Reversible inhibition

Answer 32

Inhibitor binds temporarily

Question 33

Irreversible inhibition

Answer 33

Inhibitor binds permanently

Question 34

Describe a competitive inhibitor

Answer 34

* molecular shape complementary to the active site and similar to the substrate * competes with the substrate for the active site * when it does bind to the active site it prevents the substrate from binding which decreases the rate of reaction * reversible * increasing substrate concentration will decrease the effect as it is more likely that a substrate molecule will form an enzyme-substrate complex * increasing inhibitor concentration will decrease the rate of reaction but the final mass of product ends up the same

Question 35

Describe non-competitive inhibitor

Answer 35

* binds to the enzyme at an allosteric site and changes the shape of the enzyme * doesn't compete with substrate * changes the overall shape of the enzyme which means the substrate can no longer bind and no enzyme-substrate complexes are formed * can be reversible or irreversible * increasing substrate concentration doesn't reduce inhibition * increasing inhibition concentration decreases rate of reaction and decreases final mass of product formed

Question 36

What is an immobilised enzyme

Answer 36

Enzyme molecules bound to an inert material, over which the substrate molecules move

Question 37

Name ways of immobilising enzymes

Answer 37

* alginate beads | * cellulose microfibrils

Question 38

How can being able to control the rate of flow of the substrate over the beads be used

Answer 38

Slowing the flow rate will give more time for enzyme-substrate complexes to form and so yield more product

Question 39

How does being in a 'micro-environment' affect the enzymes activity

Answer 39

The enzymes are less susceptible to changes in pH, temperature and the action of chemicals such as organic solvents

Question 40

Advantages of immobilising enzymes

Answer 40

* enzymes easily recovered and reused * product is not contaminated by the enzyme * increased stability and function over a wider range of temperature and pH than free enzymes * several enzymes with different temperature and pH optima can be used at the same time * enzymes can be easily added or removed- greater control over the reaction

Question 41

What is a biosensor

Answer 41

A device that combines a biomolecule, such as an enzyme, with a transducer, to produce an electrical signal which measures the concentration of a chemical.

Question 42

What is the role of the selectively permeable membrane in a biosensor

Answer 42

Allows the metabolite to diffuse through to the immobilised enzyme, whilst preventing the passage of other molecules

Question 43

How does a biosensor turn the metabolite into an electrical signal

Answer 43

* binds to the active site of enzyme and turns into product | * product combines with the transducer which turns the chemical energy into an electrical signal