3.1.4:2 Enzymes

Question 1

What is an enzymes function?

Answer 1

To catalyse reactions

Question 2

How do enzymes speed up reactions?

Answer 2

Lower the activation energy of the reaction it’s catalysing

Question 3

What are the two models of enzyme function?

Answer 3

Induced-fit

Lock and key

Question 4

What do the properties of an enzyme depend on?

Answer 4

The tertiary structure of the active site

Ability to combine with complementary substrates

Question 5

What is formed in a catalysing processes?

Answer 5

Enzyme-substrate complex

Question 6

What is specificity?

Answer 6

Each enzyme can only combine with one substrate because of their complementary shapes

Question 7

What is activation energy?

Answer 7

The least amount of energy required to activate atoms of molecules to a state in which they can undergo a chemical reaction

Question 8

What is it the functional part of the enzyme called?

Answer 8

Active site

Question 9

What are enzymes made from?

Answer 9

Amino acids

Question 10

Describe the structure of an enzyme?

Answer 10

Globular protein
Tertiary structure
Depression in the side (active site)
Specific as each active site fits one substrate

Question 11

Why are enzymes needed in living things?

Answer 11

The activation energy in living things is too high as the temperature is too low so the enzymes lower the activation energy

Question 12

What happens to the enzyme when the temperature or pH is too high or low in the reaction?

Answer 12

It denatures

Question 13

What happens when an enzyme denatures?

Answer 13

When the temperature is too high there is enough energy to break hydrogen bonds in the tertiary structure so the active size changes shape. It’s no longer complementary to the substrate so enzyme-substrate complexes can’t be formed. No products are formed.

Question 14

What is the difference between an anabolic and catabolic reaction?

Answer 14

Anabolic builds bonds

Catabolic breaks bonds

Question 15

What is wrong with the lock and key theory?

Answer 15

It suggests that enzymes are rigid but they’re not

They can alter their shape

Question 16

What factors affect the rate of an enzyme controlled reaction?

Answer 16

Temperature
pH
Concentration of substrate
Concentration of enzyme

Question 17

How do we express the rate of an enzyme controlled reaction

Answer 17

Turnover number
The number of substrate molecules which one molecule of enzyme can turn into product per minute
(usually 100,000’s)

Question 18

How can rate of reaction be measured?

Answer 18

Increase in product over time
Decrease in substrate over time
(Tangent on graph)

Question 19

Why does rate on reaction in an enzyme controlled reaction tend to decrease over time?

Answer 19

Substrate is converted into product
Less and less substrate molecules for enzymes to act upon
Less enzyme-substrate complexes formed

Question 20

What conditions must be satisfied for a reaction to take place naturally?

Answer 20

Substrates must combine with enough energy to alter the arrangement f their atoms to form products
The free energy of the products must be less than that of the substrates
Activation energy

Question 21

What is the induced fit model?

Answer 21

The proximity of the substrate leads to a change in the enzyme that forms the functional active site
As the shape changes, the enzyme puts statin on the substrate molecule
The strain distorts a particular bond or bonds in the substrate
This lowers the activation energy needed to break the bond

Question 22

What is the effect of rise in temperature on enzyme action?

Answer 22

Increases the kinetic energy of molecules
The molecules move around more rapidly and so collide with each other more often
More enzyme substrate complexes are formed in a given time
Rate of reaction increases

Question 23

What happens to enzyme activity when the temperature is too high?

Answer 23

Hydrogen (and other) bonds in the enzyme break
The polypeptide chains become unravelled as the tertiary structure changes
The active site changes shape so the substrates are no longer complementary
Fewer enzyme substrate complexes formed
Enzymes denatured
Rate of reaction decreases

Question 24

Why is our body temperature 37C when the optimum for many human enzymes is 40C?

Answer 24

Additional energy would be needed to maintain higher temperatures
Other proteins may be denatured at a higher temperature
If the temperatures were higher and a further rise in temperature occurred, due to illness for example, enzymes might denature

Question 25

What would be the pH number of a solution with a hydrogen ion concentration of 1x10^-9?

Answer 25

9

Question 26

Why are pH changes in organisms likes to reduce an enzyme’s action that to denature it?

Answer 26

pH fluctuations in organisms are usually small

Question 27

What happens to rate of reaction at low enzyme concentration?

Answer 27

Too few enzyme molecules for all substrate molecules to find an active site at one time
Rate of reaction is half the maximum possible for the number of substrate molecules

Question 28

What happens to rate of reaction at intermediate enzyme concentration?

Answer 28

With more molecules available, all substrate molecules can occupy an active site at the same time
Rate of reaction increases to its maximum

Question 29

What happens to rate of reaction at high enzyme concentration?

Answer 29

Addition of further enzyme molecules has so effect
All substrates have an active site already
Rate of reaction is at a constant level

Question 30

What enzyme inhibition?

Answer 30

Directly or indirectly interfering with the functioning of the active site to reduce its activity

Question 31

What are the two main types of enzyme inhibitors?

Answer 31

Competitive

Non-competitive

Question 32

How do competitive inhibitors slow enzyme function?

Answer 32

They have a similar molecular shape to the substrate
They can occupy the site of an enzyme
They are not permanently bound to the active site so substrates can eventually take their place
This makes the rate slower

Question 33

What determines the effect of competitive inhibitors?

Answer 33

The difference in concentration of the inhibitor and substrate
More inhibitor will slow the reaction more

Question 34

How do non-competitive inhibitors work?

Answer 34

Attach to a binding site on the enzyme that is not the active site
This affects hydrogen bonding and disulphides bridges, altering the tertiary structure and 3D shape
The active site changes shape so is no longer complementary
The enzymes function is blocked no matter how much substrate is present
Rate of reaction is reduced