1.4.2 Enzymes

Question 1

What do enzymes do generally?

Answer 1

Act as catalysts without undergoing permanent change themselves

Question 2

What are enzymes made of in terms of type of protein?

Answer 2

Globular proteins

Question 3

What are enzymes structure?

Answer 3

Very specific precise tertiary structure

Question 4

How many substrates fit an enzyme?

Answer 4

One enzyme for one type of substrate

Question 5

Where does the substrate bind to the enzyme?

Answer 5

The active site

Question 6

What is the active site? How is it formed?

Answer 6

A hollow depression on one side

Formed by the peptide, hydrogen, ionic and di-sulfide bonds in the tertiary structure

Question 7

What describes the substrate shape compared to the active site?

Answer 7

Complementary

Question 8

Why are enzymes needed in the body?

Answer 8

The activation energy of the majority of reactions are too high at the temperature in which living organisms exist

Question 9

What is activation energy?

Answer 9

The least amount of energy required for a reaction to be able to take place

Question 10

How do enzymes affect activation energy?

Answer 10

They reduce the activation energy

Question 11

How do enzymes reduce activation energy?

Answer 11

Anabolic - The enzymes hold the substrate in such a way that they react more easily

Or

Catabolic - They put a strain on the bond that will more easily break

Question 12

What are the two theories that describe the way enzymes work?

Answer 12

Lock and key

Induced fit

Question 13

What is the lock and key hypothesis?

Answer 13

The enzyme and substrate appear perfectly complementary

They form and enzyme-substrate complex and then produces products

Question 14

What does the lock and key theory suggest?

Answer 14

The structure of an enzyme is rigid when it isn’t

Question 15

What is the induced fit hypothesis?

Answer 15

When the substrate enters the active site it induces a slight change in the shape of an enzyme due to temporary ionic bonding - this allows the enzyme-substrate complex to form
As the active site changes the enzyme puts a strain on the substrate molecule allowing products to be formed

Question 16

What is denaturation?

Answer 16

When the active site changes due to changes in the tertiary structure of the molecule (usually hydrogen bonds - occasionally ionic if pH change) and so it is no longer complementary to the substrate

Enzyme-substrate complexes cannot form

Question 17

What factors affect the rate of an enzyme controlled reaction?

Answer 17

Temperature
pH
Enzyme concentration
Substrate concentration

Question 18

How do you express the rate of the enzyme controlled reaction?

Answer 18

The speed that the enzyme works in the turnover number

This is the number of substrate molecules which one enzyme molecule can turn into product per minute

Question 19

How can rate be measured?

Answer 19

Increase in product over time

Or

Decrease in substrate over time

Question 20

How do you work out the rate of reaction off a graph based on volume collected and time?

Answer 20

Draw a tangent to the curve of the graph and work out the gradient by doing Y / X

Question 21

What do you have to do to acquire the results for the affect of temperature?

Answer 21

You have to do lots of experiments for different temperatures

Question 22

What happens as temperature increases?

Answer 22

As more energy is added the enzyme and substrate molecules have more kinetic energy
Therefore there are more frequent successful collisions above the activation energy
More enzyme-substrate complexes form
More product produced
Faster rate of reaction

Question 23

What is the optimum temperature for enzymes? Why?

Answer 23

37 degrees

Enzyme-substrate complexes form at the fastest turnover number before denatured as they have the most kinetic energy

Question 24

What happens as temperature is increasing past 37 degrees or optimum temperature?

Answer 24

The enzyme becomes denatured
The high energy causes the hydrogen bonds to break
The tertiary structure will break down as the polypeptide chain unravels
The active site is changed
The substrate is no longer complementary
Fewer enzyme-substrate complexes form
The rate of reaction decreases

Question 25

How can pH reduce the rate of reaction?

Answer 25

The change in concentration of hydrogen ions disrupts the ionic bonding holding the tertiary structure together
It affects the charges in R-groups therefore the ionic temporary bonds with the substrate no-longer occur
Shape of the active site changes (denatures)
Substrate is no longer complementary
Fewer Enzyme-substrate complexes form
The rate of reaction decreases

Question 26

How does substrate concentration affect the rate of enzyme reactions?

Answer 26

Initial increase in rate of reaction
Gradual increase to plateau
Eventual plateau as there are only so many enzymes to form enzyme-substrate complexes therefore the rate of reaction can only go so far

Question 27

As the volume of enzyme is reduced why does the rate of reaction decrease?

Answer 27

There are less enzymes therefore less active sites available to deal with the substrate
There will be less enzyme-substrate complexes and less products reduced

Question 28

Why does the product produced always stay the same - when changing the enzyme concentration?

Answer 28

There’s always the same amount of substrate to break down

It just takes longer with fewer active sites available

Question 29

What are the two types of inhibitors?

Answer 29

Competitive

Non-competitive

Question 30

How do competitive inhibitors work?

Answer 30

They combine with the enzyme molecules at the active site as they have a similar and complementary shapes to the substrate
They compete with the substrates for the active site - they are not permanently bound
This forms enzyme-inhibitor complexes
They reduce rate of reaction

Question 31

Example of competitive inhibitors at work?

Answer 31

Antibiotics and other drugs can destroy bacteria by combining with the enzymes that allow bacteria to function

Question 32

How do non-competitive inhibitors work?

Answer 32

The inhibitor binds to the enzyme somewhere other than the active site
This affects the hydrogen and di-sulfide bonding which alters the tertiary structure
The active site is changed and the substrate is no longer complementary
No enzyme-substrate complexes can form

Question 33

In a question if a substrate and a random molecule is shown what should you recognise?

Answer 33

That the two are complementary and so the molecule is likely to be an inhibitor of the other

Question 34

What is the control of metabolic pathways?

Answer 34

End-point inhibition

The end product of a series of reactions can prevent its own production