Enzymes 2

Question 1

What are the functions of inorganic activators. Give examples of some

Answer 1

May stabilise: 
- substrate in a certain form
- intermediates in the reaction
- structure of AS
May participate in the catalytic act by reacting electrostatically with negatively charged groups

E.g.: usually cations - Mg2+, Fe2+, Mn2+, Zn2+, Cu2+, K+, Na+

Question 2

Are organic or inorganic activators cofactors? What is the other?

Answer 2

Inorganic activators: cofactors

Organic activators: co-enzymes

Question 3

What are the functions of organic activators? Give some examples

Answer 3

They have no catalytic function, but do transfer functional groups. They act like an extra substrate and participate in all metabolic pathways. Usually derived from B-vitamins and are non-protein.

Question 4

What is proteolytic activation?

Answer 4

An enzyme that is produced in an inactive form is called a zymogen. When its needed the zymogen is split by a proteolytic enzyme to give the active enzyme.

Question 5

Give some examples of zymogens undergoing proteolytic activation

Answer 5

Blood clotting cascade proteins, which are synthesised in the liver:

• prothrombin –> thrombin (vitamin k is essential for this, warfarin inhibits vitamin k so reduced clotting ability - used in medicine and also rodenticides)
• fibrinogen –> fibrin

Digestive enzymes:

• trypsinogen –> trypsin
• chymotrypsinogen –> chymotrypsin

Question 6

What effect can phosphorylation have on enzymes?

Answer 6

Can increase or decrease their activity, it is usually stimulated by specific hormones

Degrading enzyme - glycogen phosphorylase - decreased activity
Synthesising enzymes - glycogen synthase - increased activity

Question 7

What are allosteric enzymes?

Answer 7

Enzymes with 2 or more subunits therefore 2 or more active sites.

Question 8

What effect does the bonding of a substrate have to an allosteric enzyme?

Answer 8

The bonding of a substrate causes a change in form of the enzyme –> co-operatively
It results in the sigmoidal kinetics when plotted against [S] like O2 in RBCs

Question 9

What are and what binds to effector binding sites on an allosteric enzyme?

Answer 9

As well as and AS each subunit has 1 or more effector binding site. Specific non-substrate molecules bond here and either:

• increase overall enzyme activity (allosteric activator)
• decrease overall enzyme activity (allosteric inhibitor)

Question 10

Briefly describe the actions of a) oxidoreductases b) transferases c) hydrolases

Answer 10

a) oxidoreductases - oxidation and reduction reactions
b) transferases - transfer of functional groups
c) hydrolases - split bonds but the addition of H2O