2.4: Enzymes

Question 1

What is an enzyme?

Answer 1

Biological catalysts that speed up the rate of chemical reaction by decreasing activation energy
Substrate binds to active site to form an enzyme substrate complex

Made up of globular proteins

Question 2

What is the active site?

Answer 2

Specific and unique in shape due to the specific folding and bonding of the tertiary structure of the protein

Question 3

What are the two enzyme mechanisms?

Answer 3

• Lock and key - enzyme and substrate bind perfectly
• Induced fit - active site slightly changes shape it fit substrate

Question 4

What is an apoenzyme?

Answer 4

An inactive form of the enzyme
When they experience activation they turn into a holoenzyme

Question 5

What are features of cofactors?

Answer 5

• Inorganic (minerals)
• Temporarily bound to the enzyme - when they bind they will activate it
  e.g Chlorine ions bind to amylase

Question 6

What are featuress of coenzymes?

Answer 6

• Organic (vitamins)
• Temporarily bound
  e.g NADP

Question 7

What are features of prosthetic groups?

Answer 7

• Permenantly bound by covalent bonds
  e.g Iron in haem group or zinc in carbonic anhydrase

Question 8

What does the enzyme carbonic anhydrase do?

Answer 8

It contains a zinc ion permemantly bound, as a prosthetic group, to it’s active site.
* Found in erythrocytes (rbc)
* catalyses the interconversion of CO2 and H2O to carbonic acid
* this then breaks down into protons and hydrogencarbonate ions

Question 9

What does temperature do to enzymes?

Answer 9

1. When temperature increases the molecules gain more kinetic energy and start to move quicker
2. There is a higher chance for the enzyme and substrate to collide with each other (more successful collisions)
3. This increases the rate of reaction
4. After it reaches it optimum temperature the enzymes denature and the rate of reaction slows down

Question 10

What does pH levels do to enzymes?

Answer 10

• Too high or to low a pH will interfere with the charges in the amino acids in the active site
• Causes ionic/hydrogen bonds to break
• Alters tertiary structure and changes the shape of the active site and the enzyme denatures
• Enzymess have different optimal pH values that they work at

Question 11

What happens when substrate concentration increases?

Answer 11

1. There will be more substrate to form enzymes substrate complexes
2. The rate of reaction will increase only to a certain extent
3. It is a limiting factor because all the enzymes are occupied
4. Max ESC is formed

Question 12

What happens when enzyme concentration increases?

Answer 12

1. There will be more enzymes to form enzymes substrate complexes
2. The rate of reaction will increase only to a certain extent
3. It is a limiting factor because therer would be no substrate left
4. Max ESC is formed

Question 13

What is an inhibitor?

Answer 13

A chemical that could bind to the enzyme in a certain way to reduce the rate of chemical reaction

Question 14

What is a competitive inhibitor?

Answer 14

An inhibitor that has a similar shape to the substrate molecule that is complementary to the active site. Therefore it competes with the substrate for the active site

Question 15

What is a non - competitive inhibitor?

Answer 15

It binds to the allosteric site . The binding causes a conformational change (structural change) to the active site of the enzyme. This means it is no longer complementary to the substrate

Question 16

What does the competitive inhibitor do?

Answer 16

• Similar structure to substrate
• Competes with the substrate for the same active site
• Less active sites are avaliable
• Less ESC formed and the rate of reaction decreases
• When there is a higher concentration of substrate molecules it can outcompete and restore the Vmax

Question 17

What does the non-competitive inhibitor do?

Answer 17

• Binds to the allosteric site
• Changes the 3D structure of the active site
• Active site no longer complementary to substrate
• Less ESC formed so the rate of reaction decreases
• HIgher substrate concentration cannot restore Vmax

Question 18

What is end product inhibition?

Answer 18

The products of some reactions are reversible inhibitors for the enzymes involved in controlling the reaction.
* This enables the reaction to be controlled

Question 19

What does end product inhibition do?

Answer 19

If there is a lot of product present, it will inhibit the enzymes and cause the reaction to slow or stop
This prevents resources being wasted

Question 20

What is enzyme degradation?

Answer 20

Cells are continuously degrading old enzyme molecules to their component amino acids and synthesising new enzyme molecules from amino acids

Question 21

What are the advantages of enzyme degradation?

Answer 21

• It eliminates abnormally shaped proteins that might otherwise accumulate annd harm the cell
• The regulation of metabolism in the cell by eliminating any superfluous enzymes