Enzymes

Question 1

What are enzymes?

Answer 1

Biological catalysts that speed up chemical reactions

Question 2

Substrate

Answer 2

A molecule that bonds to the active site of an enzyme to be catalysed by it in a reaction

Question 3

Structure of an enzyme: active site

Answer 3

The tertiary structure of its protein(s) fold into the specific shape
Which determines the active site where substrate binds to because they are SIMILAR (not the same) in shape

Question 4

Enzyme substrate complex

Answer 4

When the substrate is bonded to the active site of an enzyme forming this

Question 5

How do enzyme substrate complexes form?

Answer 5

When the substrate and enzyme’s active site collide successfully
Because the active site is complementary to substrate after changing tertiary structure in induced fit model
So forms complex

Question 6

Products

Answer 6

What is a product of the enzyme catalysed reaction eg proteins being broken down to amino acids

Question 7

What is the job of enzymes?

Answer 7

To increase rate of a reaction
Because it’s a biological catalyst

Question 8

How do enzymes increase rate of reaction?

Answer 8

When an enzyme-substrate complex is formed the substrate bonds are put under stress
Causing the activation energy of this catalysed reaction to lower (energy required to break bonds in substrate) so reaction is more likely to occur

Question 9

What is the induced fit model?

Answer 9

Explains how an enzyme’s active site can bond to a substrate
Because they are complementary to each other however the active site has to mould itself

Question 10

Description of the induced fit model in action

Answer 10

Substrate moves towards enzyme’ active site, and fits inside because they are SIMILAR in shape
The active site changes shape so it can be complementary to substrate and bind to form an enzyme-substrate complex (puts bonds under stress in substrate)

Question 11

Why do only substrate molecules cause the enzyme’s active site to distort?

Answer 11

Because the bonds between amino acids in the active site of the enzyme and the substrate won’t be formed so the shape of the tertiary structure won’t change

Question 12

What was the original theory for how enzymes are complementary to substrates?

Answer 12

The lock and key theory which said all enzymes active sites are already complementary to the substrates

Question 13

A product time graph

Answer 13

Tells us the amount of product produced over the course of an enzyme catalysed reaction
Could be under certain conditions such as increased temperature etc

Question 14

Description of a product/ substrate time graph for an enzyme catalysed reaction

Answer 14

Initially rapid because there is a high concentration of substrate molecules thus more enzyme substrate complexes
Decreasing rate of reaction in middle because no. Of substrate molecules is decreasing as more is made to products so lower rate of reaction (less enzyme substrate complexes formed)
Plateaus because no more substrate molecules collide with active site = stopped

Question 15

How to find rate of reaction at a specific point on a product/substrate time graph?

Answer 15

Draw tangent at that point

Question 16

What’s important to remember about finding the rate of reaction at a specific point using a tangent?

Answer 16

Can only be done on a product time graph
Because some graphs already have rate of reaction on the y axis so simply use the y axis

Question 17

What factors affect enzyme catalysed reaction?

Answer 17

Temperature
Substrate/ enzyme concentration
pH
Competitive/ non competitive inhibitors

Question 18

How to describe the factors effect on INCREASING enzymes rate of reaction?

Answer 18

This factors causes ____
Which increases frequency of successful collisions between enzyme’s active site and substrate in a haven time because ____
So number of enzyme-substrate complexes formed increase in a given time
Therefore more products are formed in a given time, increases rate of reaction

Question 19

How to describe the factors effect on DECREASING enzymes rate of reaction?

Answer 19

This factor causes _____
Which decreases the frequency of successful collisions between enzyme and substrate in a given time because _____
So number of enzyme-substrate complexes formed decrease in a given time
So less products formed in a given time, decreasing rate of reaction

Question 20

How to find a factor-rate graph?

Answer 20

Decide on specific factor eg pH
Select enzyme and measure amount of product formed over time
Draw graph for the results
Repeat for other pHs
Find the rates at the same time for each graph and draw a factor-rate graph

Question 21

Temperature as a factor on a factor-rate graph description

Answer 21

Rate increases with the temperature
Before reaching an optimum
Then the rate decreases rapidly

Question 22

Why does enzyme rate of reaction increase with increasing the temperature?

Answer 22

Increasing temp causes an increase in kinetic energy
Which increases frequency of successful collisions between enzyme’s active site and substrate because there is more rapid movement between molecules
So number of enzyme-substrate complexes formed increase
Therefore more products are formed in a given time, increases rate of reaction

Question 23

Optimum temperature reached

Answer 23

When the temperature is at this point, it has achieved maximum frequency of collisions between active site and enzyme
So rate is at maximum peak = temperature is no longer limiting factor

Question 24

Why does the rate of reaction drop rapidly after going beyond the optimum temperature?

Answer 24

Because at higher temps enzymes begin vibrating more rapidly so bonds in the tertiary structure end up breaking
Which changes the tertiary structure thus active site
So no longer is complementary to substrate and can’t catalyse reaction

Question 25

Can the enzyme renature after it has denatured to increased temperature?

Answer 25

No because the tertiary structure had changed too much

Question 26

Low pH

Answer 26

High concentration of H+ ions

Question 27

High pH

Answer 27

Low concentration of H+ ions

Question 28

Enzymes optimum pH

Answer 28

When the rate of reaction for an enzyme to catalyse is at its highest Depends on the enzyme

Question 29

pH-rate graph description

Answer 29

On the x axis, at the optimum pH there is a massive increase in rate of reaction But before and after that pH the rate decreases very rapidly to 0

Question 30

Why does rate of reaction decrease above and below optimum pH in enzyme catalyse reaction?

Answer 30

Because changing from the optimum disrupts tertiary structure of enzyme causing a change in shape of the active site So less enzyme substrate complexes are formed because the active site no longer complementary to substrate Sometimes extreme pH causes complete denaturation

Question 31

How to find the pH of a solution given the concentration of hydrogen ions?

Answer 31

pH = -log [H+] H+ = the concentration of hydrogen ions

Question 32

How does increasing the substrate concentration (but keeping enzyme conc constant) increase rate of reaction?

Answer 32

Because at low concentrations not all active sites are occupied so conc is limiting factor Increasing number of substrate molecules Increases the frequency of successful collisions between substrate and active site increases Increasing no. Of enzyme substrate complexes thus rate of reaction

Question 33

Relationship between rate of reaction and substrate concentration

Answer 33

Directly proportional Until it stops increasing and reaches its V max despite substrate concentration increasing

Question 34

Enzyme’s v max

Answer 34

The maximum rate of reaction an enzyme can reach when saturated with substrate

Question 35

Why does the enzyme reach its v max?

Answer 35

Because there are no more free active sites for the extra substrate molecules to collide with So there’s no enough enzymes to form more enzyme-substrate complexes = rate of reaction stops increasing

Question 36

How does increasing the enzyme concentration (keeping substrate concentration constant) increase rate of reaction?

Answer 36

Because there are more active sites available And so increased successful collisions More enzyme substrate complexes at any point So increased rate

Question 37

How do competitive inhibitors decrease the rate of reaction

Answer 37

The comp inhibitor binds to the active site By occupying the active site the substrate cannot bind to the active site so less successful collisions Less enzyme substrate complexes formed So reduces rate of reaction

Question 38

Competitive inhibitors

Answer 38

Molecules that bind to the enzymes active site which inhibits the reaction and reduces rate of reaction because they are similar in shape to substrate so prevent enzyme- substrate complexes from forming

Question 39

Where do comp inhibitors bind to?

Answer 39

Active site

Question 40

How to offset the effect of competitive inhibitors

Answer 40

Increase substrate concentration So greater change it will occupy active site instead of inhibitors

Question 41

Rate-substrate concentration with comp an inhibitor graph

Answer 41

Will reach the v max eventually than if there were no comp inhibitor But the rate before is reduced compared to with no inhibitor

Question 42

Can irreversible competitive inhibitors be reversed by increasing substrate concentration?

Answer 42

No because it permanently binds to active site so increasing substrate concentration won’t change as it can’t bind to active site

Question 43

Non competitive inhibitors

Answer 43

Molecules that bind to the allosteric site of an enzyme which reduces rate of reaction

Question 44

Where do non comp inhibitors bind to?

Answer 44

Allosteric site

Question 45

How do non competitive inhibitors decrease rate of reaction?

Answer 45

Binds to allosteric site Causes tertiary structure of enzyme to change So active site changes shape = not complementary to substrate So enzyme substrate complexes not formed decreasing rate of reaction

Question 46

Can non competitive inhibitors be overcome by increasing substrate concentration?

Answer 46

No will never reach v max because active site changed shape So even with more substrates they can’t bind to active site

Question 47

When using enzymes in a practical what should the control be?

Answer 47

Boiled enzyme because then the enzyme denatures and thus cannot form enzyme substrate complexes

Question 48

What happens when enzymes denature?

Answer 48

The bonds between r groups in tertiary structure are broken so tertiary structure is disrupted Causing polypeptide chains to unfold and destroy active site Substrate is no longer complementary to enzyme's active site

Question 49

Feed back inhibition loops

Answer 49

enzyme 1 --> enzyme 2 --> enzyme 3 If a product released in an enzyme catalysed reaction 3 inhibits enzyme 1 to turn off its own production