cofactors and coenzymes

Question 1

define coenzyme

Answer 1

organic cofactor not permanently attached to the protein

Question 2

define cofactor

Answer 2

non-protein component necessary for effective functioning of an enzyme (ions or organic molecules)

Question 3

describe the similarities between cofactors, coenzymes and prosthetic groups.

Answer 3

• coenzymes and prosthetic groups are both cofactors
• cofactors and prosthetic groups can be organic or inorganic

Question 4

describe differences between cofactors, coenzymes and prosthetic groups.

Answer 4

• coenzymes are organic cofactors - not permanently attached to the protein
• prosthetic groups are cofactors that are permanently attached to the enzyme

Question 5

why is the chloride ion necessary for the correct formation of the amylase active site is a cofactor, not a coenzyme or prosthetic group

Answer 5

• it is organic (coenzymes are organic)
• it is not permanently attached (prosthetic groups are)

Question 6

explain why zinc ions that form an important part of the structure of carbonic anhydrase is a prosthetic group, not a cofactor or coenzyme.

Answer 6

• it is permanently attached (stating cofactor is ambiguous as they are both)
• inorganic (coenzymes are organic only)

Question 7

give two examples of coenzymes synthesised from vitamins in our diet.

Answer 7

• NAD (vitamin B3)
• NADP (vitamin B3)

Question 8

define inorganic precursor enzyme

Answer 8

enzyme that requires biochemical change for it to become active

Question 9

explain why inactive precursor enzymes may be produced

Answer 9

• to prevent enzymes from causing damage within the cells producing them when released
• when enzymes action needs to be controlled

Question 10

describe 3 ways in which inactive precursor may be activated.

Answer 10

• adding a cofactor
• action of another enzyme
• change in conditions

Question 11

define apoenzyme

Answer 11

protein that forms an active enzyme by combination with a cofactor

Question 12

define holoenzyme

Answer 12

active form of an enzyme

Question 13

define zymogens

Answer 13

inactive enzymes that require a biochemical change (change in conditions/acted on by another enzyme) to become an active enzyme.

Question 14

define proenzymes

Answer 14

inactive enzymes that require a biochemical change (change in conditions/acted on by another enzyme) to become an active enzyme.

Question 15

give 2 examples of inactive precursor enzymes and describe how they are activated

Answer 15

• pepsinogen: becomes pepsin when exposed to stomach acid (low pH)
• trypsinogen: becomes trypsin when cleaved into active form by enteropeptidase