Enzymes as biological catalysts

Question 1

What do enzymes do?

Answer 1

They are catalysts that speed up chemical reactions and make up the process of metabolism.
They speed up the rate at which a reaction reaches equilibrium

Question 2

What characteristics define all enzymes?

Answer 2

Catalysts
Proteins
Efficient
Specific
Potent - each enzyme molecule can convert many substrate molecules into product per second

Question 3

What must enzymes pass to allow the reaction to occur?

Answer 3

Activation energy barrier

Question 4

What is the transition state?

Answer 4

The transition state is the reaction intermediate species which has the greatest free energy

Question 5

How do enzymes reduce the activation energy?

Answer 5

They provide an alternative reaction pathway

Question 6

What is a cofactor?

Answer 6

A small metal ion molecule that increases the enzymes catalytic activity

Question 7

What is a coenzyme?

Answer 7

A small organic molecule that increases the enzymes catalytic activity

Question 8

What do metal cofactors form in the centre of an enzyme?

Answer 8

A metal co-ordination centre called a metalloprotein

Question 9

What do coenzymes change during the course of the reaction?

Answer 9

Their charge or structure

Question 10

What is a prosthetic group?

Answer 10

A tightly bound coenzyme

Question 11

What is an apoenzyme?

Answer 11

An enzyme without a cofactor

Question 12

What is a holoenzyme?

Answer 12

An enzyme with a cofactor

Question 13

What are some examples of a cofactors?

Answer 13

Zinc, Iron, Copper, coenzymes such as ATP, NAD and FAD

Question 14

What do many vitamins function as?

Answer 14

Coenzymes

Question 15

What is an example of an enzyme that shows induced fit?

Answer 15

Hexokinase which changes shape as glucose binds to the active site, ATP is a co-substrate

Question 16

What are some examples of active sites?

Answer 16

The three pancreatic protrases that contain reactive serine residue which catalyse the hydrolysis of peptides

Question 17

What 2 factors affect enzyme activity?

Answer 17

Temperature and pH

Question 18

What is an isoenzyme?

Answer 18

An isoform of an enzyme that catalyses the same reaction but has different properties and structure

Question 19

When can different isoenzymes be synthesized?

Answer 19

Foetal and embryonic development
Different tissues
Different cellular locations

Question 20

What is an example of an isoenzyme?

Answer 20

Lactate dehydrogenase which when containing 2 subunits in the heart promotes anaerobic respiration but when in muscle promotes anaerobic respiration

Question 21

What is an example of reversible covalent modification?

Answer 21

Phosphorylation

Question 22

What are phosphorylation reactions carried out by?

Answer 22

Kinases and dephosphorylation carried out by phosphatases

Question 23

What does the irreversibel covalent modification result in?

Answer 23

Irreversible activation of enzymes

Question 24

What is a zymogen?

Answer 24

An inactive precursor of an enzyme that is irreversibly transformed into an active enzyme by the cleavage of a covalent bond

Question 25

What are some examples of zymogens?

Answer 25

Enzymes found in pancreas, small intestine, digestive enzymes, blood clotting and clot dissolving enzymes