Enzymes

Question 1

What are enzymes?

Answer 1

Globular proteins with specific tertiary structure, which catalyse reactions.

Question 2

What does it mean that enzymes catalyse reactions?

Answer 2

They reduce the activation energy of chemical reactions, increasing the rate of reaction without being consumed.

Question 3

What is an example of an intracellular enzyme?

Answer 3

Catalase

hydrogen peroxide=>water+oxygen

Question 4

What are two examples of extracellular enzymes, and what reaction do they catalyse?

Answer 4

Amylase
starch=>glucose
Trypsin
proteins=>amino acids

Question 5

What is the lock and key model of enzyme action?

Answer 5

The substrate attaches to the complementary active site of the enzyme, forming the ESC (enzyme-substrate complex).
This then becomes the EPC (enzyme-product complex).

Question 6

What is the induced-fit theory of enzyme action?

Answer 6

Like the lock-and-key model, but the active site is constantly being reshaped from interaction with the substrate.

Question 7

What are cofactors?

Answer 7

Inorganic molecules that play a role in a multi-step pathway or form part of the active site of an enzyme.

Question 8

What are coenzymes?

Answer 8

The same as cofactors but are organic molecules.

Question 9

What are prosthetic groups?

Answer 9

Cofactors that are tightly bound to the enzyme protein.

Question 10

What is an example of a cofactor, and what enzyme does it work with?

Answer 10

Cl- (chloride ions)

with Amylase in the digestion of starch

Question 11

What is an example of a coenzyme, and what enzyme pathway does it work with?

Answer 11

NAD

transfers hydrogen atoms in respiration

Question 12

What is an example of a prosthetic group, and what enzyme does it work with?

Answer 12

Zn2+ (zinc ions)

with Carbonic Anhydrase in the metabolism of carbon dioxide

Question 13

How does increasing temperature increase the rate of enzyme-controlled reactions?

Answer 13

Higher temperature corresponds to individual molecules having greater kinetic energy so moving faster and colliding more. This results in the ESC being formed more often and the activation energy being more easily reached, increasing the rate of reaction.

Question 14

How does very high temperature cause enzymes to denature

Answer 14

The kinetic energy of molecules strains the bonds holding the enzyme together. The weak hydrogen and ionic bonds break first. This changes the shape of the active site so that it is no longer complementary to the substrate.

Question 15

How can pH cause an enzyme to denature?

Answer 15

Ions in acidic or basic solutions interfere with hydrogen and ionic bonds holding the enzyme together. This changes the shape of the active site.
All enzymes have an optimum pH.

Question 16

What other factors other than temperature and pH can affect the rate of an enzyme-controlled reaction?

Answer 16

The substrate concentration.
The enzyme concentration.
Enzyme inhibitors.

Question 17

What is an enzyme inhibitor?

Answer 17

Any substance which slows down an enzyme controlled reaction by affecting the enzyme molecule.

Question 18

How does a competitive enzyme inhibitor work?

Answer 18

The inhibitor has a similar shape to the substrate.
It competes with the substrate to enter the active site.
The competitive inhibitor enters and blocks the active site, preventing formation of the ESC.

Question 19

How do non-competitive enzyme inhibitors work?

Answer 19

The inhibitor binds to an allosteric site on the enzyme, this changes the shape of the active site without competing with the substrate.

Question 20

What is a non-reversible enzyme inhibitor?

Answer 20

An inhibitor that permanently binds to the enzyme with strong covalent bonds.

Question 21

What is a reversible enzyme inhibitor?

Answer 21

An inhibitor that does not permanently bind (weak hydrogen or ionic bonds)

Question 22

What is an example of an enzyme inhibitor used as a metabolic poison, and how does it work?

Answer 22

Cyanide inhibits enzymes in mitochondria, preventing aerobic respiration.

Question 23

What is an example of an enzyme inhibitor used as a medicinal drug, and how does it work?

Answer 23

Penicillin competitively inhibits an enzyme in bacteria, preventing the production of the peptidoglycan cell wall.

Question 24

What is end-product inhibition?

Answer 24

When a product of an enzyme reaction pathway inhibits one of the enzymes involved in the pathway. This slows the rate of reaction if the concentration of the product is too high in negative feedback.