Enzymes

Question 1

What are enzymes?

Answer 1

globular proteins that act as biological catalysts

Question 2

How does an enzyme act as a biological catalyst?

Answer 2

alter rate of chemical reaction by lowering activation energy required without undergoing permanent change themselves

Question 3

What is required to start a chemical reaction?

Answer 3

-must collide with sufficient energy
-energy of products must be lower than substrates/reactants
-minimum amount of energy to start reaction-activation energy

Question 4

What is the structure of an enzyme?

Answer 4

Specific region- active site

Question 5

What is an active site?

Answer 5

forms small depression within the much larger enzyme molecule

Question 6

What is the active site made up of?

Answer 6

relatively small number of amino acids

Question 7

What is the molecule that the enzyme acts upon called?

Answer 7

substrate

Question 8

What is formed when the active site and substrate collide?

Answer 8

enzyme-substrate complex

Question 9

How is an enzyme substrate complex formed?

Answer 9

substrate and active site collide
substrate held within active site that temporarily form bonds between certain amino acids of substrate and active site

Question 10

What does the lock and key enzyme model suggest?

Answer 10

enzyme active site specific shape to particular substrate
enzyme active site and substrate are exactly complimentary
when substrate collides with active site an enzyme substrate complex is formed

Question 11

What does the enzyme induced fit model propose?

Answer 11

active site and substrate not EXACTLY complimentary
active site forms as enzyme and substrate interact
proximity of substrate alters shape to form functional active site
enzyme moulds itself around substrate
enzyme substrate complex is formed

Question 12

What two changes are most frequently measured to determine the length of enzyme-catalysed reactions?

Answer 12

-formation of products
-reduction in starch concentration

Question 13

How can we measure the change in a rate of reaction?

Answer 13

measure gradient at chosen point

Question 14

How can we obtain a gradient from an enzyme-catalysed reaction ?

Answer 14

equal to gradient of tangent to curve at point
tangent- point at which straight line touches the curve without cutting across it
normal line- line that pass through a point at 90•
gradient- A/B

Question 15

How do we create a control when measuring the rate of an enzyme-catalysed reaction?

Answer 15

enzyme and substrate concentration constant
all possible inhibitors absent
active site and substrate mustn’t be complementary

Question 16

How does temperature affect the rate of an enzyme-catalysed reaction?

Answer 16

rise in temperature, increase in kinetic energy of molecules
molecules more likely to collide as moving rapidly
enzyme and substrate in contact more often in a given time
more successful collisions, more enzyme substrate complexes, increases rate of reaction
HOWEVER LIMITING…
temperature rise causes bonds to break
active site changes shape
harder to form enzyme substrate complex, slower rate
higher temperature, enzyme denatured (permanent) no enzyme substrate complex as cannot function

Question 17

What is the pH of a solution?

Answer 17

Measure of its hydrogen ion concentration

Question 18

What does each enzyme have in terms of pH?

Answer 18

An optimum pH

Question 19

How does pH affect enzyme action?

Answer 19

-alters charges on amino acids that form active site therefore substrate can longer bind for e-s complex
-depending on significance of pH change, bonds maintaining tertiary structure break and active site changes shape

Question 20

How does enzyme concentration affect the rate of reaction?

Answer 20

Excess of substrate-increase in amount of enzyme-proportionate increase in rate of reaction
If substrate limiting-increase in enzyme concentration-not enough substrate available for increase in active site-no effect on rate

Question 21

How does substrate concentration affect the rate of reaction?

Answer 21

Increase in substrate concentration- more substrate available to bind to active site (more opportunities)-rate of reaction increases-more e-s complexes formed-substrate becomes limiting factor-no further effect

Question 22

What are enzyme inhibitors?

Answer 22

Substances that directly or indirectly interfere with function of active site

Question 23

What is a competitive inhibitor?

Answer 23

Substances which bind directly to active site of enzyme

Question 24

What is a non-competitive inhibitor?

Answer 24

Substances which bind indirectly to the enzyme (allosteric site) which changes the shape of the active site

Question 25

How does competitive inhibition work?

Answer 25

Molecule structurally similar to substrate competes and binds to active site
Prevents substrate from binding
Effects are reversible as inhibitor not permanently bound to active site

Question 26

How can we prevent the affects of competitive inhibition?

Answer 26

Increase substrate concentration, effect of inhibitor reduced

Question 27

How does non-competitive inhibition work?

Answer 27

Inhibitor binds to allosteric site
Binding to allosteric site alters shape of active site
Non-competitive inhibitors do not compete with substrate
Change in active site shape stops substrate from binding

Question 28

Why does increasing substrate concentration not effect non-competitive inhibition?

Answer 28

Substrate and non-competitive inhibitor do not compete for the same site. Substrate for active site whereas non-competitive inhibitor for allosteric site