Lesson 14 - Cofactors, coenzymes and prosthetic groups in Enzymes

Question 1

Cofactor definition

Answer 1

Non-protein components necessary for the effective functioning of an enzyme

Question 2

Inorganic cofactors:

Answer 2

Obtained via the diet as minerals
- Iron ion
- Calcium ion
- Chloride ion
- Zinc ion

Question 3

What does chloride do in the breakdown of starch by amylase?

Answer 3

Chloride ion binds to enzyme. This changes the active site of the enzyme to correctly fit the substrate shape of starch.

Question 4

What coenzyme is used to catalyse respiratory reactions?

Answer 4

NAD (nicotinamide adenine dinucleotide)

Question 5

NAD (nicotinamide adenine dinucleotide)

Answer 5

• Transfers hydrogen between molecules involved in respiration
• Derived from vitamin B3
• Organic molecule

Question 6

Role of coenzyme NADP?

Answer 6

• Role in photosynthesis
• Organic cofactor derived from vitamin B3

Question 7

Coenzyme A?

Answer 7

• derived from vitamin B5
• Essential in the break down of fatty acids and carbohydrates in respiration

Question 8

Prosthetic group?

Answer 8

Non-protein component of a conjugated protein. It is a permanent cofactor.

Question 9

Examples of prosthetic groups?

Answer 9

• Haem group in haemoglobin and catalyse
• Zinc ions in carbonic anhydrase (necessary for the metabolism of carbon dioxide)

Question 10

Coenzymes:

Answer 10

Large, complex, organic molecules based on carbon element.

Question 11

What is an inactive precursor enzyme?

Answer 11

Some enzymes are produced in an inactive form, as they can cause damage within cells producing them or to tissues when they are released.
They can also be enzymes whose action needs to be controlled and only activated under certain conditions.

Question 12

How are precursor enzymes activated?

Answer 12

Change in tertiary structure, changing the shape of the active site.
- Achieved via the addition of a cofactor
- Change in temp or pH
- Addition of another enzyme

Question 13

Name of precursor protein before cofactor is added?

Answer 13

Apoenzyme

Question 14

Name of precursor enzyme after cofactor is added?

Answer 14

Holoenzyme

Question 15

What activates Zymogens?

Answer 15

Environmental factors

Question 16

What activates proenzymes?

Answer 16

The addition of another enzyme.
Eg. proteases

Action of another enzyme cleaves certain bonds in the molecule.

Question 17

Example of a zymogen?

Answer 17

Pepsinogen:
- Released into stomach to digest proteins.
pH in stomach brings about transformation into the active enzyme pepsin. This adaptation protects the body tissues against the digestive action of pepsin.

Question 18

Enzyme activation and the blood-clotting mechanism?

Answer 18

• Blood clotting is an important response to tissue damage.
• Platelets aggregate at the site of tissue damage. Release clotting factors (such as factor X)
• Factor X relies on cofactor vitamin K for activation.
• Factor X catalyses the conversion of prothrombin into the enzyme thrombin by cleaving certain bonds in the molecule, altering the tertiary structure.
• Thrombin is a protease and catalyses the conversion of soluble fibrinogen to insoluble fibrin fibres. Fibrin molecules and platelets form a blood clot.
• Series of successive enzyme activations in blood clotting is called the coagulation cascade.