3.1.4.2 Many proteins are enzymes

Question 1

what is an enzyme?

Answer 1

biological catalysts that speed up the rate of a chemical reaction in organisms without getting used up

Question 2

where can enzymes catalyse metabolic reactions?

Answer 2

at a cellular level (respiration) and extracellularly (digestion)

Question 3

what is formed when an enzyme binds to a substrate?

Answer 3

enzyme-substrate complex

Question 4

how do enzymes speed up metabolic reactions?

Answer 4

by lowering the activation energy of a reaction due to bending bonds

Question 5

what are the two models of enzymes?

Answer 5

• lock and key
• induced fit

Question 6

what does the lock and key model of an enzyme suggest?

Answer 6

the shape of the active site is exactly complementary to the specific substrate molecule

Question 7

what does the induced fit model of an enzyme suggest?

Answer 7

the active site can change shape slightly so it is complementary to the substrate, this distorts bonds in the substrate and therefore lowers activation energy

Question 8

why is the induced fit model better than the lock and key model?

Answer 8

research has been done into inhibitors, suggesting that the structure of an enzyme is not as rigid as it was assumed to be, meaning that it can change shape

Question 9

how does temperature affect enzyme activity until the optimum temperature?

Answer 9

• increase in temperature causes an increase in kinetic energy
• this causes molecules to move around more and increases the chances for more successful collisions
• this increases the rate of enzyme activity

Question 10

how does temperature affect enzyme activity beyond the optimum temperature?

Answer 10

• hydrogen and other bonds break
• this disrupts the secondary and tertiary structure
• causes denaturation so rate of enzyme activity decreases

Question 11

denaturation of enzymes due to temperature is…

Answer 11

permanent

Question 12

what is pH?

Answer 12

the concentration of hydrogen ions of solution

Question 13

what is the formula for calculating pH?

Answer 13

-log[H+]

Question 14

how does pH affect the rate of enzyme activity?

Answer 14

• changes ionic charges within the enzyme
• causes hydrogen and ionic bonds to change
• more likely to decrease the rate of enzyme activity than denature enzymes

Question 15

denaturation of enzymes due to pH is…

Answer 15

generally reversible

Question 16

what is competitive inhibition?

Answer 16

• inhibitor has a similar shape to substrate
• molecule binds to active site of enzyme before substrate can
• prevents e-s complex forming

Question 17

what is non-competitive inhibtion?

Answer 17

• molecule binds to allosteric site (site in the enzyme other than the active site)
• changes the shape of the active site / alters tertiary structure
• no longer complementary to the substrate so no e-s complexes form

Question 18

when competitive inhibitors are present, how would the rate of enzyme activity change if the concentration of the substrate increased?

Answer 18

enzyme activity would increase as substrates out-compete inhibitor to form e-s complexes

Question 19

when non-competitive inhibitors are present, how would the rate of enzyme activity change if the concentration of the substrate increased?

Answer 19

no change as active site changes shape so no e-s complexes can form

Question 20

what happens to e-s complexes during competitive inhibition?

Answer 20

less e-s complexes are formed

Question 21

what happens to e-s complexes during non-competitive inhibition?

Answer 21

no e-s complexes are formed