Factors affecting enzyme actions

Question 1

Factors

Answer 1

Substrate concentration
Enzyme concentration 
Temperature
PH
Inhibitors

Question 2

Explain how active site enables the substrate to then bind to the enzyme

Answer 2

Change in tertiary structure affecting active site

Substrate now complementary

Question 3

Substrate/enzyme concentration limiting

Answer 3

Limiting factor at beginning of reaction but eventually the enzyme become saturated (as all the active sites are filled)

increasing the substrate concentration won’t further increase the rate of reaction

Question 4

S/C conc graph - what does it show

Answer 4

Keeping the concentration of the enzyme constant while increasing the concentration of substrate results in an increase in rate of reaction

However, at a certain concentration, the rate of reaction reaches a maximum level with all active sites being used

After, increasing the substrate level doesn’t increase the rate of reaction

Question 5

What is the limiting factor in first part of graph (S/E conc)

Answer 5

Substrate concentration as if substrate concentration is increased, rate of reaction increases

Question 6

Limiting factor at first part of graph (e conc)

Answer 6

Enzyme conc as if enzyme concentration is increased, rate of reaction increases

Question 7

Limiting factors at 2nd part of graph (e conc)

Answer 7

Number of substrate molecules, as if you increase the enzyme concentration, the rate doesn’t further increase

Question 8

Enzymes at low temperatures

Answer 8

Described as inactive

Reversible reaction as it doesn’t change tertiary structure of enzymes

Inactive - little kinetic energy, few collisions between enzyme & substrate, few ES complexes, low rate of reaction

Question 9

Denatured

Answer 9

• heat causes atoms to vibrate
• hydrogen bonds break first as they are the weakest bonds
• tertiary structure changes
• shape of active site changes
• active site & substrate no longer complementary shapes
• no/fewer E-S complexes, reduced rate of reaction

Not reversible reaction

Question 10

pH calc

Answer 10

Convert stand form to decimal
Log
+/-

Question 11

pH

Answer 11

Major effect on enzyme activity as it can alter the tertiary structure of the protein molecule

Extremes of pH denature enzymes by making or breaking hydrogen and/or ionic bonds (as these bonds rely on electrostatic attractions between ions or partial charges), not reversible

Question 12

PH denatured

Answer 12

High or low pH

• ionic bonds break
• tertiary structure changes
• shape of active site changes
• active site & substrate no longer complementary
• no E-S complexes
• reduced rate of reaction

Question 13

How can this link to picking as a preserving technique

Answer 13

Active site changed

No E-S complexes formed

Question 14

Enzyme inhibitors

Answer 14

Reduce rate of reaction

2 types of inhibition - reversible & irreversible

Question 15

Reversible inhibition

Answer 15

Inhibitor doesn’t permanently damage the enzyme tertiary and if the inhibitor is removed it functions normally again

Question 16

Competitive inhibition

Answer 16

Inhibitor is similar shape to the substrate molecule

It competes to bind on the active site of the enzyme, forming enzyme-inhibitor complex

If concentration of inhibitor is fixed, the percentage of the inhibition can be reduced by increasing the substrate concentration

As 2 molecules are competing, the more substrate molecules there are, the less likely it is that the inhibitor will bind to the active site

Question 17

Action of competitive inhibitor

Answer 17

Competitive inhibitor interferes with active site of enzyme so substrate cannot bind

Question 18

Non-competitive inhibition

Answer 18

Inhibitor is not competing for the active site but joins to the enzyme molecule somewhere else on its structure (allosteric)

The inhibitors shape is different to that of the substrate, the inhibitors form a complex with the enzyme and this changes the tertiary of the protein

Active site shape changes, so that the substrate is no longer a complementary shape

Changing conc of substrate makes no difference to the level of inhibition of the rate of reaction

Question 19

Action of non-competitive inhibitor

Answer 19

Non-competitive inhibitor changes shape of enzyme so it cannot bind to substrate

Question 20

How to tell if competitive or non-competitive inhibitor

Answer 20

1. Perform experiment with only enzyme present and keep adding more substrate until you get maximum rate of reaction (to determine Vmax)
2. All other factors (e.g. temp, pH) need to remain constant
3. Repeat experiment with the inhibitor present
4. Plot a graph of results

Question 21

Competitive inhibitor graph

Answer 21

Adding more substrate

Less probability inhibitor gets into active site

Rate increases as inhibition decreases

Eventually reaches Vmax

Question 22

Non-competitive inhibitor graph

Answer 22

Adding more substrate

Inhibitor can still enter allosteric site & change tertiary structure and change shape of active site

Rate doesn’t increase, stays the same, inhibition stays the same