C5- Enzymes

Question 1

Enzyme

General definition

Answer 1

Globular proteins that act as a biological catalyst

They catalyse reactions that affect metabolism

Lower activation energy needed for a reaction to begin

Question 2

Metabolism

Answer 2

All the chemical reaction in a cell

catabolism= breaking down
large -> small

Anabolism= Building up
small –> large

Question 3

Extracellular enzymes

Answer 3

Their effect is outside the cells that produce them

e.g. amylase

Question 4

Intracellular enzymes

Answer 4

Their effect is inside the cells that produced them

e.g. Catalase
–> catalyses hydrolysis of hydrogen
peroxide

Question 5

Lock and key hypothesis

Answer 5

enzyme has an area called the active site that is complimentary to the shape of the substrate

When bound this forms the enzyme substrate (e-s) complex

substrate then reacts and the product or products are formed

This forms the enzyme product (e-p) complex

Substrate is held in such a way by the enzyme that the right R groups are close enough to react. Temporary bonds form between enzyme and substrate, putting strain on the bonds in the substrate which helps the reaction along

Question 6

Induced fit hypothesis

Answer 6

modified version of lock and key hypothesis, where initially the substrate is not complimentary to the active site.

When the enzyme substrate (e-s) complex is formed the enzyme changes shape slightly as the substrate binds to the enzyme,

allowing the reaction to take place due to lowered activation energy

Question 7

Active site

Answer 7

part of the protein molecule with the specific 3D shape to bind to one specific complimentary substrate

Question 8

Substrate

Answer 8

A substance used or acted on by a process or enzyme

Question 9

Effect of temperature on enzyme activity

Answer 9

As temp increases the kinetic energy of particles increases

Enzyme and substrate move faster and collide more frequently.

More frequent successful collisions

More enzyme-substrate complexes are formed in a given time

Question 10

Enzymes at too high temperatures

Answer 10

Bonds holding the secondary and tertiary structure together are broken

This changes the precise 3D shape of the enzyme

Active site changes shape

The substrate is no longer complementary (so does not fit)

Enzyme no longer functions

Denature= irreversible

Question 11

Enzymes at Lower temperatures

Answer 11

Enzymes are INACTIVE at low temperatures.

They do not denature at low temperatures.

At low temperatures enzyme and substrate molecules have less kinetic energy so fewer enzyme-substrate complexes form.

Question 12

Temperature coefficient

Q10

Answer 12

A measure of how much the rate of reaction increases for every 10C increase in temperature.

This is usually around 2

Rate at higher temperature / Rate at lower temperature

x+10/X

Question 13

How does pH effect enzyme activity

Answer 13

Hydrogen ions (H+) interact with charged R groups on amino acids.

This may alter the way in which R groups interact with each other e.g. ionic bonds may break.

The shape of the enzyme (and the shape of the active site) changes so the substrate does not fit.

Question 14

Effect of substrate concentration on enzyme activity

Answer 14

As the concentration of substrate increases, there is an increased chance of successful collisions between the enzyme and the substrate.

The rate of reaction increases up to a maximum rate, Vmax

There is a maximum rate of reaction as at high concentrations of substrate the active sites are SATURATED

Question 15

V max

enzymes

Answer 15

The maximum rate of reaction

Question 16

Point of saturation

Answer 16

All active sites are occupied by a substate

Concentration of enzyme is the limiting factor to rate of reaction

Question 17

How do inhibitors work

Answer 17

Inhibitors are substances that slow down the rate of enzyme-controlled reactions.

Inhibitors reduce the chance of the normal substrate binding to the active site.

Question 18

Competitive Inhibition

Process

Answer 18

inhibitor molecule has a similar shape to the substrate, so is complimentary to the active site

The inhibitor molecule binds with active site of enzyme

Inhibitor molecule prevents the binding of the substrate molecule

Question 19

Non Competitive inhibition

process

Answer 19

The inhibitor binds to the enzyme at a region which is NOT the active site - called the ALLOSTERIC SITE.
(the inhibitor is not competing with the normal substrate for the active site).
This causes the tertiary structure of the enzyme to change and the active site changes shape.
The active site is NO LONGER COMPLEMENTARY to the substrate.
The substrate cannot bind to the active site.
The enzyme is INHIBITED.

Question 20

Competitive inhibition

Effect on rate of reaction and vmax

Answer 20

Will decrease the rate of reaction BUT

The V max can still be reached IF enough substrate is present!

Question 21

Non competitive inhibition

Effect on rate of reaction and vmax

Answer 21

slows rate of reaction

V max cannot be reached

Question 22

Bonding

Reversible vs irreversible enzyme inhibitors

Answer 22

strong, covalent bonds the inhibitor cannot be removed easily and the inhibition is permanent (irreversible).

weaker hydrogen or ionic bonds the inhibitor can be easily removed and the inhibition is reversible.

Question 23

Metabolic Poisons

Answer 23

These are chemicals which inhibit the activity of enzymes involved in key metabolic reactions.

These poisons can cause illness or death.

Question 24

What is specific about the structure of the enzyme and its effect on activity

Answer 24

specific, 3D shape / tertiary structure

(formation of) active site

binds to substrate(s)

catalyses reaction

Question 25

Explain how catabolism and anabolism are related to anabolism

Answer 25

Catabolism is breaking down of molecules

anabolism is building of molecules reactions

idea of metabolism is sum of all reactions

Question 26

Catalase

Answer 26

Catalyses the hydrolysis of hydrogen peroxide into water and hydrogen

Question 27

Explain the term denatured

Answer 27

R-group interactions are disrupted

H bonds

change in tertiary structure

change in 3D shape of active site preventing binding with substrate

Question 28

Explain why a non competitive inhibitor does not need to have a similar shape to the substate molecule

Answer 28

A non-competitive inhibitor binds to an enzyme away from the active site

at an allosteric site

which has a different shape than the active site

Question 29

Explain why increasing the concentration of the substrate will never produce the V max of a reaction after a non competitive inhibitor has been added

Answer 29

Inhibitor will always be present

some enzymes always inhibited

Question 30

End product inhibition is likely to be competitive rather than non competitive

Suggest reasons for this and give an example of end product inhibition

Answer 30

End-product inhibition regulates rate of reaction

concentrations of substrate and product
determine reaction rate

(so must be) competitive

substrate concentration has no effect in non- competitive inhibition

e.g. ATP and PFK in respiration

Question 31

End product inhibition

Answer 31

When the product of a reaction acts as an inhibitor to the enzyme that produced it

Question 32

Function/ effect of end product inhibition

Answer 32

Way of controlling reactions

Preventing further accumulation of certain substances in cells

Question 33

Cofactors

general

Answer 33

some enzymes work better in the Prescence of other molecules or ions called cofactors

cofactors are a non protein part of an enzyme

Question 34

2 Types of cofactors

Answer 34

Organic molecules (coenzymes)

Inorganic ions

Question 35

Cofactor specific example

Answer 35

Chloride ions are cofactors for the enzyme amylase

Question 36

inorganic cofactors

Answer 36

ensure the active site is the correct shape by changing the shape of the active site

do not take part in the reaction

Question 37

Coenzymes

Answer 37

Transfer chemical groups or atoms between molecules in reactions

often vitamins

Question 38

Protein hydrolysis PAG

why leave albumen and pepsin solution in water bath before mixing

Answer 38

Temperature equilibration or preincubation

Ensures both solutions are at the desired temperature

Question 39

Protein hydrolysis PAG

Why is it important to add the same volume of biuret reagent to each sample

Answer 39

Controls the saturation of the solutions

Affects the time recorded for the colour change to take place

Question 40

Protein hydrolysis PAG

Biuret reagent can sometimes act as an enzyme inhibitor, why do we carry the test out in samples not directly from the reaction mixture

Answer 40

Since biuret reagent acts as an enzyme inhibitor, it inhibits pepsin causing rate of reaction to slow down, reducing colour change