Module 2.4 - Enzymes

Question 1

Define enzymes

Answer 1

Globular proteins with specific tertiary structures

Question 2

How do enzymes get these specific tertiary structures?

Answer 2

Primary base sequence determines the specific tertiary structure

Question 3

Do endotherms need enzymes adapted for extreme temperatures?

Answer 3

No as they maintain their own internal body temperature, so maintain the optimum temperatures for enzymes by thermoregulation

Question 4

How do heterotrophs digest food?

Answer 4

Consume other organisms and digest them inside the body (e.g. animals)

Question 5

How do saprophytic feeders digest food?

Answer 5

Release enzymes onto food for it to be digested outside the body and then absorb the monomers (e.g. fungi, bacteria)

Question 6

Define extracellular enzymes

Answer 6

Catalyse outside cells

Most digestive enzymes

Question 7

Define intracellular enzymes

Answer 7

Catalyse inside cells (within cytoplasm / on membranes)

Question 8

How do enzymes catalyse a reaction?

Answer 8

Reduce activation energy required by providing a different route for the reaction

Question 9

Define activation energy

Answer 9

Minimum energy required for reaction to take place

Question 10

Induced fit hypothesis

Answer 10

As the substrate binds to the active site, the enzyme changes shape slightly.
The active site is tighter around the substrate molecules.
Oppositely charged groups on the substrate and active site interact and hold the substrate molecule in place (ESC).
The enzyme’s shape change puts strain on the bonds in the substrate which destabilises it, causing the reaction to occur more easily.
Enzyme product complex is formed and as it is a different shape to the reactant it’s released from the active site.

Question 11

Define temperature coefficient

Answer 11

Measure of rate of change of a reaction when the temperature is increased by 10°C

Question 12

How will a low pH affect enzymes?

Answer 12

A low pH means that there are more H+ ions, which will attract negative parts of the enzyme and repel positive parts
This interferes with the hydrogen and ionic bonds giving the enzyme its tertiary structure and therefore specific active site

Question 13

Define enzyme inhibitors

Answer 13

Molecules that slow down the rate of an enzyme controlled reaction

Question 14

Main points about competitive inhibitors

Answer 14

Similar shape to enzymes’ substrate
Complementary to active site so they can bind with it and block it, forming an enzyme-inhibitor-complex
Prevents ESCs forming, slows rate of reaction, no products formed
Do not bind permanently (action is reversible)

Question 15

Main points about non-competitive inhibitors

Answer 15

Fit into allosteric site on enzyme
Alters tertiary structure of enzyme so changes shape of active site
No ESCs can form, rate of reaction decreases
Bind permanently

Question 16

Three cofactors

Answer 16

Coenzymes
Prosthetic groups
Inorganic ion cofactors

Question 17

Define cofactors

Answer 17

Substances that must be present to ensure that an enzyme-controlled reaction takes place at the right rate

Question 18

Points about coenzymes

Answer 18

Small, organic, non-protein molecules
Able to bind to active site at same time as substrate or just before
Changed by the reaction then converted back to original state (usually by a different enzyme)
E.g. vitamin B12 (nicotinamide) is used to make the coenzyme required for Pyruvate Dehydrogenase

Question 19

Points about prosthetic groups

Answer 19

Permanent parts of some enzymes (permanent coenzyme)
Vital to 3D shape, function and charges on enzyme
E.g. carbonic anhydride contains Zn2+ prosthetic group, allows red blood cells to combine CO2 and H2O to produce carbonic acid

Question 20

Points about inorganic ion cofactors

Answer 20

Increase reaction rate
Combine with enzymes or substrates which helps ESC form more easily by altering charge or shape of ESC
E.g. amylase breaks down starch into maltose molecules, and will only function properly if in the presence of chloride ions

Question 21

Points about potassium cyanide

Answer 21

Non-competitive inhibitor of enzyme cytochrome oxidase needed for respiration
Inhibiting this enzyme decreases use of oxygen so ATP can’t be made
Organism has to respire anaerobically causing build up of lactic acid in blood

Question 22

Inhibitors used to treat viral infections

Answer 22

Competitive inhibitors
E.g. HIV is treated using protease inhibitors as viruses need protease enzymes to build viral coat and inhibitors prevent this happening

Question 23

Inhibitors in antibiotics

Answer 23

Treat bacterial infections by killing/stopping growth

E.g. penicillin is an inhibitor of the enzyme that helps build cell walls in bacteria, preventing bacteria reproducing

Question 24

Inhibitors in alcohol

Answer 24

Ethylene glycol (in antifreeze) is broken down in the liver by alcohol dehydrogenase in oxalic acid which is highly toxic - can lead to death
Ethanol acts as a competitive inhibitor of alcohol dehydrogenase