Enzymes as Biological Catalysts

Question 1

What do enzymes do?

Answer 1

Speed up the rate at which a reaction reaches equilibrium

Question 2

Do enzymes affect the position of equilibrium?

Answer 2

No

Question 3

What are enzymes made of?

Answer 3

Mostly proteins but some types of RNA (ribozymes`) can also be catalysts

Question 4

What conditions are optimal for enzymes?

Answer 4

Body temperature, aqueous solution and neutral pH

Question 5

What is specificity in relation to proteins?

Answer 5

Each enzyme has a limited range of substrates. Some can distinguish stereoisomers

Question 6

What is enzyme potency?

Answer 6

Each enzyme can convert many substrate molecules into product per second

Question 7

What happens at a reaction’s transition state?

Answer 7

The reaction takes place really rapidly which is unstable for the reactants

Question 8

How do enzymes affect the transition state?

Answer 8

They bind to the reactants and make it stable, also reducing the activation energy by providing alternative pathways

Question 9

What is the transition state?

Answer 9

The reaction intermediate species which has the greatest free energy hence why it is unstable

Question 10

What causes glycogen storage disease?

Answer 10

It is an enzyme deficiency that results in failure of glycogen to enter the transition ‘phosphorylated’ state and so there is defective glycogen synthesis/breakdown

Question 11

What are the symptoms of glycogen storage disease?

Answer 11

Hypoglycaemia, hepatomegaly (liver swelling), skin and mouth ulcers, bacterial/fungal infection and bowel inflammation/irritability

Question 12

What is the treatment for glycogen storage disease?

Answer 12

Slow release glucose meal and feeding little and often to mimic glycogen conversion to glucose

Question 13

What is a cofactor?

Answer 13

Metal ions (inorganic) which many enzymes depend on for catalytic activity

Question 14

What do cofactors form with enzymes?

Answer 14

Metal co-ordination centre in the enzyme - metalloprotein

Question 15

What is a coenzyme?

Answer 15

An organic molecule which many enzymes depend on for catalytic activity

Question 16

What do coenzymes do?

Answer 16

Mostly associate with the coenzyme transiently and change charge or structure during the reaction but are regenerated eg VITAMINS

Question 17

What are tightly bound coenzymes called?

Answer 17

Prosthetic groups

Question 18

What is an enzyme without a cofactor called?

Answer 18

Apoenzyme

Question 19

What is an enzyme with a cofactor called?

Answer 19

Holoenzyme = apoenzyme + cofactor

Question 20

What do cofactors do?

Answer 20

Stabilise transition states

Question 21

Where does the substrate bind in the enzyme?

Answer 21

Active site - a cleft or crevice that contains amino acids essential for catalytic activity for highly specific reactions

Question 22

What is the lock and key model?

Answer 22

Active site of the unbound enzyme is complementary to the shape of the substrate

Question 23

What is the induced fit model?

Answer 23

Binding of the substrate induces a conformational change in the enzyme resulting in complementary fit

Question 24

What are isozymes?

Answer 24

Isoforms of enzymes - they catalyse the same reaction but have different properties and structure

Question 25

Where are isozymes synthesised?

Answer 25

During different stages of foetal and embryonic development

Question 26

Where are isozymes present?

Answer 26

In different tissues and in different cellular locations

Question 27

In lactate dehydrogenase what are the 2 subunits and what do they do?

Answer 27

H (heart) - promotes aerobic respiration

M (muscle) - promotes anaerobic respiration

Question 28

What is the role of creatine kinase?

Answer 28

It is a dimeric protein which binds to the muscle sarcomere. M form is produced in skeletal muscle (MM), B form is produced in brain (BB) and the heart produces both types = heterodimer (MB). Brain type in blood suggests stroke/tumour, whilst heart type suggests heart attack.

Question 29

What is the role of enzyme activation by phosphorylation?

Answer 29

Can convert enzymes to active or inactive forms by protein kinases - fast, reversible and found in all cells - especially in energy generation

Question 30

What are zymogens?

Answer 30

Inactive precursors of an enzyme

Question 31

What happens in irreversible covalent modification to regulate enzyme activity?

Answer 31

Results in activation of enzymes. Zymogens are irreversibly transformed into active enzymes by cleavage of a covalent bond

Question 32

What are some examples of digestive enzymes?

Answer 32

Trypsin, chymotrypsin, carboxypeptidase A and B, elastase, pepsin and phospholipase

Question 33

What are some examples of blood coagulation factors?

Answer 33

Factors VII, IX, X, XI, and XIII, kallikrein and thrombin

Question 34

What are some examples of enzymes in blood clot dissolving?

Answer 34

Plasminogen, and plasminogen activator

Question 35

What are some examples of enzymes involved in programmed development?

Answer 35

Chitin synthetase, cocoons and collagenase