4 - ENZYMES

Question 1

What are enzymes?

Answer 1

They are globular proteins which act as biological catalysts becauses they speed up metabollic reactions in living organisms without running out by lowering the activation energy

Question 2

What are catabolic enzymes?

Answer 2

Enzymes which break down substances

Question 3

What are anabolic enzymes?

Answer 3

Enzymes which synthesise large molecules

Question 4

What are intracellular enzymes?

Answer 4

Enzymes which act within the cells which they are made in

Question 5

What are extracellular enzymes?

Answer 5

Enzymes which leave the cells they are made in by exocytosis and act outside on other target cells

Question 6

Describe the lock and key model.

Answer 6

The active site of an enzyme is specific to substrates with a complementary shapes and when they collide they form temporary bonds in an enzyme-substrate complex (ESC)

Question 7

Describe the induced fit theory.

Answer 7

Although the shape of the active site is complementary to that of a substrate, subtle changes occur in the shape of the side chains or R groups of amino acids which give them a more precise conformation in the active site

Question 8

What is a co-factor?

Answer 8

A substance that aids the function of an enzyme, either in the form of a co-enzyme (temporarily bonded) or a prosthetic group (permanently, covalently bonded)

Question 9

What is the role of a co-factor?

Answer 9

• eases the formation of ESCs
• acts as co-substrate by combining with the substrate to make it fit perfectly in the enzyme’s active site
• changes the charge distribution on the surface of the enzyme or the substrate to make the temporary bonds between them easier to form

Question 10

What happens once an ESC forms?

Answer 10

The enzyme acts anabollically or catabollically, forming an enzyme-product complex (EPC) before release the products

Question 11

What factors affect the rate of enzyme-controlled reactions?

Answer 11

Temperature, pH, enzyme concentration, substrate concentration, cofactors and inhibitors

Question 12

What is Vmax?

Answer 12

The maximum rate of reaction/activity of an enzyme

Question 13

What is the effect of temperauture on enzyme activity?

Answer 13

• increases kinetic energy of the enzyme and the substrate so they collide together more, forming more ESCs
• at the enzyme’s optimal temp, Vmax is achieved
• further increases to the temp cause H bonds to breqk but there is chance of their reformation
• once temp is increased even further, the enzyme denatures

Question 14

What is the affect of pH on enzyme activity?

Answer 14

• different enzymes have different optimum pH levels at which they work most efficiently and achieve Vmax
• further changes to pH cause H bonds to break but there is chance of their reformation
• once pH changes even further, the enzyme denatures

Question 15

How does an enzyme become denatured?

Answer 15

• hydrogen bonds and ionic bonds in its tertiary structure break
• the shape of the active site changes permanently
• the enzyme can no longer carry out its function

Question 16

What is the effect of enzyme/ substrate concentration on enzyme activity?

Answer 16

• as concentration (of one) increases, rate of reaction increases
• concentration becomes limiting factor of the reaction, since the rate begins to slow
• once the concentration increases further, Vmax is achieved
• further increases in concentration have no effect on the rate
• the concentration of the other now becomes the limiting factor

Question 17

What are competitive inhibtors?

Answer 17

Inhibitors which:

• can fit into active site of an enzyme without reacting
• compete with subtrate molecules for access to the active site
• affects activity depending on concetration
• can be minimised by raising the concentration of substrate
• have reversible effects on the enzyme as they detach themselves after a while

Question 18

What are non-competitive inhibitors?

Answer 18

Inhibitors which:

• binds to allosteric site (the place on an enzyme where a molecule that is not a substrate may bind)
• change the shape of the molecule, preventing it from working
• effect is independent of substrate concentration and irreversible

Question 18

What are metabollic inhibitors?

Answer 18

Poisons and medicines which inhibit the metabollic reactions of cells for an adverse or beneficial effect