Enzymes

Question 1

What are enzymes?

Answer 1

Globular proteins which speed up biochemical reactions and so are called biological catalysts

Question 2

What type of structure do enzymes have? What does this determine?

Answer 2

Tertiary structure - determines their 3D shape and so the substrate they join to

Question 3

Why is the active site - part of the enzyme molecule - a specific shape?

Answer 3

To allow the substrate molecule to enter the active site and form an enzyme substrate complex

Question 4

How does the shape of the active site compare to the shape of the substrate?

Answer 4

They may not be precisely complementary

Question 5

What happens as the substrate binds?

Answer 5

The enzyme changes shape slightly

Question 6

What is the enzyme changing shape theory called and what is it a modified form of?

Answer 6

Induced fit model - modified form of the lock and key model of enzyme action

Question 7

What is the activation energy?

Answer 7

The minimum energy needed to start a chemical reaction

Question 8

How do enzymes impact activation energy?

Answer 8

Enzymes lower the activation energy of the reactions that they catalyse

Question 9

Enzymes increase the rate of reaction without….?

Answer 9

Being used up

Question 10

What is the rate of an enzyme catalysed reaction dependent on?

Answer 10

The rate of successful collisions between the enzyme and the substrate

Question 11

What does successful collisions between the enzyme and the substrate lead to?

Answer 11

The formation of an enzyme substrate complex and then a product

Question 12

What factors affect the speed at which enzymes convert reactants to products? (5)

Answer 12

Temperature
PH
Concentration of enzyme
Concentration of substrate
Concentration of inhibitors (competitive and non competitive)

Question 13

How does temperature impact the rate of enzyme controlled reactions?

Answer 13

An increase in temperature results in an increase in the numbers of successful collisions between the enzyme and substrate molecules as they gain kinetic energy.

Question 14

What happens to enzyme controlled reactions beyond optimum temperature?

Answer 14

The increased vibrational energy of the enzyme causes ionic and hydrogen bonds to break, disrupting the tertiary structure. The substrate can no longer fit into the active site. Enzyme activity decreases and eventually stops. The enzyme is denatured - this change is irreversible

Question 15

What is pH a measure of?

Answer 15

The concentration of hydrogen ions (pH = -log10 [H+])

Question 16

What happens if the environment of an enzyme deviates either side of the optimum pH?

Answer 16

The change in hydrogen ion concentration will change the ionic charges within the enzyme. This will cause disruption of both the secondary and tertiary structure of the enzyme and so affect the shape of the active site. Fewer enzyme substrate complexes are formed and the rate of reaction decreases. Further changes in pH result in no activity at all and the enzyme is denatured. Denaturation due to a change in pH is generally reversible

Question 17

How does enzyme concentration impact the rate of enzyme controlled reactions?

Answer 17

Increasing the enzyme concentration of a biochemical reaction results in an increase in the rate of reaction. As more enzyme is added, more active sites are available to form enzyme substrate complexes and so more product is formed per second. If the substrate is in excess and not limiting, the rate of reaction continues to rise

Question 18

How does substrate concentration impact the rate of enzyme controlled reactions?

Answer 18

For a fixed amount of enzyme, increasing the substrate concentration results in an increase in the rate of reaction (the substrate is acting as a limiting factor). Once there is sufficient substrate to saturate the active sites, increasing substrate concentration results in no further increase in rate (substrate is no longer limiting)

Question 19

What is an inhibitor?

Answer 19

A substance that changes the rate of reaction of an enzyme

Question 20

How does concentration of competitive reversible inhibitors affect the rate of enzyme controlled reactions?

Answer 20

As concentration of competitive reversible inhibitors increases, rate of reaction decreases as the active sites are temporarily blocked by inhibitors so substrates cannot bind to them

Question 21

How does concentration of non competitive reversible inhibitors affect the rate of enzyme controlled reactions?

Answer 21

As concentration of non competitive reversible inhibitors increases, rate of reaction decreases as the shape of the enzyme (not the active site) is altered by the inhibitors