Enzymes

Question 1

What is an enzyme?

Answer 1

Enzymes are tertiary structure proteins which catalyse reactions.

Question 2

What is the function of enzymes?

Answer 2

To lower the activation energy of a reaction

Question 3

Do enzymes get used up in reactions?

Answer 3

No

Question 4

What is the activation energy?

Answer 4

The certain amount of energy that all reactions require before they occur.

Question 5

What part of an enzyme attaches to a substrate?

Answer 5

The active site.

Question 6

Describe the shape of an active site.

Answer 6

Specific and unique in shape

• this is due to the specific folding and bonding in the tertiary structure of the protein

Question 7

Why is the unique shape of the active site in an enzyme important?

Answer 7

It ensures that enzymes can only bind to substrates that are complementary in shape.

Question 8

What is the lock and key model?

Answer 8

The enzymes active site is a fixed shape and due to random collisions the substrate can collide and attach to the enzyme which will produce an enzyme-substrate complex. Once the enzyme-substrate complex has formed, the charged groups within the active site are thought to distort the substrate and therefore lower the activation energy. The products are then released and the enzyme active site is empty and ready to be reused.

Question 9

What is the induced-fit model?

Answer 9

Induced fit is when the enzymes active site slightly changes shape to mould around the substrate. When enzyme-substrate complex occurs due to the enzyme moulding around the substrate it puts strain on the bonds and therefore lowers the activation energy. The products are then removed and the enzymes active site returns to its original shape.

Question 10

What factors affect the rate of enzyme controlled reactions?

Answer 10

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

Question 11

How does temperature affect enzyme controlled reactions?

Answer 11

Too low temp
- not enough kinetic energy
- less successful collisions between enzyme and substrate
- fewer enzyme-substate complexes will form

Too high temp
- too much kinetic energy
- active site will change shape + enzyme will denature due to bonds breaking
- enzyme-substrate complexes cannot form

Question 12

How does pH affect enzyme controlled reactions?

Answer 12

• too high/too low a pH will interfere with charges in the amino acids in the active site
• the active site will change shape
• the enzyme denatures and fewer enzyme-substrate complexes form

Question 13

How does substrate concentration affect enzyme controlled reactions?

Answer 13

If there is insufficient substrate, the reaction will be slower as there will be fewer collisions between the enzyme and substrate.

Question 14

How does enzyme concentration affect enzyme controlled reactions?

Answer 14

If there is insufficient enzymes, the enzymes active site will become saturated with substrate and unable to work any faster.

Question 15

How do competitive inhibitors affect enzyme controlled reactions?

Answer 15

• they have a similar shape as the substrate and can bind to active site.
• prevents substrate from binding and a reaction occurring
• if more substrate is added this will out-compete the inhibitor and knock them out of the active site

Question 16

How do non-competitive inhibitors affect enzyme controlled reactions?

Answer 16

• they bind to the enzyme away from the active site called the allosteric site
• causes the active site to change shape and substrate can no longer bind regardless of how much substrate is added