2.1.4 - Enzymes

Question 1

Describe feedback inhibition

Answer 1

When a product of a reaction acts as an inhibitor to the enzyme that produces it.

Question 2

What type of mechanism is feedback inhibition

Answer 2

Negative feedback

Question 3

What type of shape change occurs when a noncompetitive inhibitor binds to an enzyme

Answer 3

Conformational

Question 4

What’s the site that NC inhibitors bind to

Answer 4

Allosteric

Question 5

Site that competitive inhibitors bind to

Answer 5

Active site

Question 6

Describe a graph comparing comp. inhibition with no inhibitor (rate against substrate concentration)

Answer 6

Rate of reaction reduced as inhibitor competes with substrate. Max rate can still be reached if substrate conc high enough

Question 7

Describe a graph comparing non-comp. inhibition with no inhibitor (rate against substrate concentration)

Answer 7

Rate of reaction reduced as enzyme active site altered. Max rate can’t be reached by raising substrate conc

Lowers Vmax

Question 8

Why is the first enzyme in a pathway more likely to be inhibited in feedback inhibition

Answer 8

Most energy efficient

Question 9

Explain the term biological catalyst

Answer 9

Proteins used in metabolism that lower activation energy

Question 10

Describe an enzyme graph of rate against temperature

Answer 10

Initially increases
At a certain temperature (optimum) the rate peaks
Rate decreases rapidly past this point
Rate stops at a certain temperature

Question 11

Why can some inhibitors bind to active sites

Answer 11

They have a similar shape to that enzyme’s substrate molecule, so its shape is complimentary to the enzyme’s active site.

Question 12

Describe a graph of rate against substrate concentration.

Answer 12

Increasing substrate conc increases the rate of reaction -> more substrate molecules entering active sites and forming ESCs

Vmax = all active sites occupied at highest concentration

Graph plateaus at Vmax and enzyme concentration is the limiting factor

Question 13

Compare cofactor/coenzyme binding to prosthetic group binding

Answer 13

COFACTOR :
Temporary
Ionic / hydrogen bonds

PROSTHETIC GROUP :
Permanent
Covalent bonds

Question 14

What are the differences between cofactors and coenzymes

Answer 14

COFACTORS:

• Derived from minerals in the diet (e.g. iron or calcium)
• inorganic

COENZYMES :

• derived from vitamins
• organic

Question 15

What can some coenzymes do beyond just initiating conformational change?

Answer 15

Transfer important molecules to enzymes (e.g. protons and NAD+)

Question 16

What are inactive precursor enzymes and why are they the way they are

Answer 16

Enzymes produced in an inactive form.

• > In some cases, to prevent damage within the cells that produce them or to the tissues where they are released.
• > Other cases, to control enzyme action and only have them be activated under certain conditions.

Question 17

How are precursor enzymes activated

Answer 17

Addition of a cofactor/coenzyme, action of another enzyme, or a change in conditions (pH / temp) to initiate conformational change.

Question 18

What’s a precursor enzyme called pre-cofactor?

Post-cofactor?

Answer 18

Apoenzyme

Holoenzyme

Question 19

What are precursor enzymes called that undergo change in tertiary structure due to pH/temp conditions or other enzymes’ actions?

Answer 19

Zymogens or proenzymes

Question 20

What may inactive proenzymes contain?

Answer 20

Extra amino acids to be removed by hydrolysis to reveal the active site by changing tertiary structure.

Question 21

How do cofactors/coenzymes/prosthetic groups cause conformational change?

What benefit does this have?

Answer 21

By affecting the charges of the active site or the Hydrogen/Ionic bonds.

This increases the chances of the successful binding of a substrate and ESC formation.

Question 22

Give an example of a cofactor

Answer 22

Chloride ions in amylase

Question 23

Give two examples of a coenzyme

Answer 23

Vitamin B3 needed to make coenzyme NAD

Vitamins B5 needed to make coenzyme A

Question 24

Give an example of a prosthetic group

Answer 24

Zinc ion forming part of the structure of carbonic anhydrase (aid carriage of CO2)

Question 25

Give an example of a proenzyme/zymogen and explain how it becomes active

Answer 25

Pepsinogen is an inactive protease enzyme secreted in the stomach

It is inactive when first secreted by the chief cells to prevent damage to the stomach wall because pepsin is digestive

The active site is obscured by a 44 amino acid-long polypeptide chain

This is removed by the acidic pH of the stomach

Question 26

What’s the difference between proenzymes/zymogens and apoenzymes?

Answer 26

Proenzymes/zymogens require another enzyme (protease) or a change in pH/temp to achieve a change in shape.

Apoenzymes need to be activated by a change in shape (active site) by the binding of a cofactor. The activated enzyme is known as a holoenzyme.