Enzymes as Biological Catalysts

Question 1

What enzymes do?

Answer 1

Catalyse many chemical reactions
Increases reaction rate of a reaction reaches equilibrium
Does not affect equilibrium position

Question 2

What are enzymes?

Answer 2

Catalysts
Mostly proteins
Efficient
Specific
Potent

Question 3

Activation Energy Barrier

Answer 3

Energy must be added to the reactants to overcome the energy barrier, which is recovered when products are formed

Question 4

Catalyst action on Activation Energy Barrier

Answer 4

Reduces activation energy barrier

Question 5

Glycogen Storage Disease

Answer 5

Enzyme deficiency –> failure of glycogen to enter transition phosphorylated state
Glycogen –> G1P –> G6P –> Glucose

Cause - defective glycogen synthesis/breakdown
Von Gierke’s Disease - symptoms and treatment

Question 6

Coenzymes

Answer 6

Organic molecules
Associate with enzyme only transiently
Change charge or structure during reaction
Tightly bound coenzymes = prosthetic group

Example
CoA, ATP
NAD+, FAD

Most vitamins function as coenzymes

Question 7

Cofactors

Answer 7

Metal Ions
Form metal co-ordination centre in enzyme

Enzyme without Cofactor = Apoenzyme
Enzyme + Cofactor = Holoenzyme
Apoenzyme + Cofactor = Holoenzyme

Examples
- Metal Ions (e.g. Zn, Fe, Cu)

Question 8

Substrate Binding to enzyme (2)

Answer 8

Substrate binds to active site
Lock and Key - unbound enzyme complementary to substrate shape
Induced fit - binding induces conformational change

Question 9

Temperature & pH affect enzyme activity

Answer 9

There are optimum ranges for temperature and pH where the enzyme will work at its best

Question 10

Isozymes

Answer 10

Isoforms of enzymes
Catalyse same reaction but have different properties and structures

Example - Lactate Dehydrogenase
- H subunit (normal O2)
- M subunit (low O2)
- 5 isoforms
- Diagnostic

Example - Creatine Kinase
- M form (skeletal muscle)
- B form (brain)
- Heterodimer (MB)
- Appearance of specific types suggest presence of disease

Question 11

Phosphorylation

Answer 11

Reversible covalent modification
Serine, Threonine, Tyrosine
Can be activated or inactivated
Kinases and Phosphatases

Question 12

Zymogens

Answer 12

Inactive precursor of an enzyme
Cleavage of covalent bond to active enzyme

Question 13

Irreversible Proteolytic Enzymes

Answer 13

Digestive enzymes
Blood Coagulation enzymes
Enzymes involved in dissolving blood clots
Enzymes involved in programmed development