Topic 1---A: Biological molecules- 7. Factors affecting enzyme activity

Question 1

How do you measure enzyme activity?

Answer 1

1. How fast the product is made
2. How fast the substrate is broken down

Question 2

How fast the product is made (measure of enzyme activity)

Answer 2

• There are different molecules present at the end of a chemical reaction than there is at the beginning.
• By measuring the amount of end product present at different times during the experiment the reaction rate can be calculated.

Question 3

How fast the substrate is broken down (measure of enzyme activity)

Answer 3

• To produce the end products in a reaction, substrate molecules have to be used up.
• By measuring the amount of substrate molecules left at different times of the experiment the reaction rate can be calculated.

Question 4

Factos affecting enzyme activity?

Answer 4

• Temperature
• pH
• Substrate concentration
• Enzyme concentration
• Competitive inhibitors
• Non-competitive inhibitors

Question 5

Temperature

Answer 5

• Rate of an enzyme-controlled reaction increases when the temperature increases
• As there is more kinetic energy so molecules move faster
• Makes the substrate molecules more likely to collide with the enzymes active site.

Question 6

What happens if the temperature gets too high?

Answer 6

• The reaction stops
• As a rise in temperature makes makes the enzymes molecules to vibrate more
• And if the temperature goes above a cerrtain level the vibration breaks some of the bonds that hold the enzyme in shape
• So the active site changes shape and the enzyme and substrate no longer fit together
• Enzyme denatures so no lunger functions as a catalyst

Question 7

What do enzymes have that are different and what does it mean?

Answer 7

• Different enzymes can have different optimum temperatures
• This means they can denature at different times

Question 8

pH

Answer 8

• All enzymes have an optimum pH value
• Above and below the optimum pH, the H + AND OH- ions found in acids and alkalis can disrupt the ionic and hydrogen bonds that hold the enzymes tertiary structure in place.
• The enzyme becomes denatured and the active site changes shape.

Question 9

Substrate concentration

Answer 9

• Increasing the concentration of substrate increases the rate of reaction.
• There are more substrates meaning a collision between substrate and enzyme is more likely so more active sites will be occupied ( greater chance of enzyme-substrates being formed)
• This is a steady increase.
• Only true up until a ‘saturation’ point
• After that, there are so many substrate molecules compared to the enzymes molecules as all their active sites are occupied.
• So there are no free enzymes to form an enzyme- substrate complex.
• Slows down

Question 10

Enzyme concentration

Answer 10

• Increasing the concentration of enzyme increases the rate of reaction.
• As if there are more enzymes it means it’s more likely a substrate molecule is to collide with one and form an enzyme- substrate complex.
• This is a steady increase as more active sites (on the enzyme) are available.
• But if there are more enzymes compared to substrate molecules it means that some active sites will be unoccupied so enzyme- substrate complexes won’t be formed
• Substrate reaction is a limiting factor so rate of reaction levels off.

Question 11

What can enzyme activity be prevented by?

Answer 11

Enzyme inhibitors

Question 12

What are enzyme inhibitors?

Answer 12

• They are molecules that bind to the enzyme they inhibit.
• They slow down or stop enzyme-catalysed reactions.
• Enzyme inhibitors can either be competitive or non-competitive.

Question 13

Competitive inhibitor

Answer 13

• They have a similar shape to that of substrate molecules.
• They compete with the substrate to bind to the active site
• They block the active site so no substrate molecules can fit in (no enzyme- substrate complexes can be formed)

Question 14

What happens if there is a high concentration of the competitive inhibitor?

Answer 14

• They will take up nearly all the active sites so hardly any of the substrates will get to the enzyme.
• So effect on inhibition is greater.

Question 15

What happens if there is a high concentration of substrates compared to competitive inhibitors?

Answer 15

• The substrates chances of getting to the active site before the inhibitor increases so the more substrate molecules the rate of reaction will increase.
• So effect of inhibition is reduced

Question 16

Non-competitive inhibitors

Answer 16

• They bind to the enzyme away from it’s active site.
• This causes the active site of the enzyme to change shape by breaking some hydrogen bonds and forming incorrect ones in the tertiary structure.
• Substrate molecules can no longer bind to the active site (no enzyme- substrate complexes can be formed)

Question 17

Why won’t increasing the concentration of substrates not have an effect on the non-competitive inhibitor?

Answer 17

• As the non-competitive inhibitors bind to the enzyme and they don’t compete with the substrate molecules to bind to the active sites because there are different shapes.
• So enzyme activity will still be inhibited.

Question 18

What happens to an enzymes shape and function when it is denatured?

Answer 18

• The bonds that hold the enzyme in place are broken which alters the shape of the active site meaning it is no longer a complementary shape to the substrate.
• So the enzyme can’t catalyse a reaction.

Question 19

What does saturation point mean?

Answer 19

It’s the point by which all active sites are occupied by the substrate molecules.