Enzymes

Question 1

What type of biological molecule are enzymes?

Answer 1

They are proteins.

Question 2

What are enzymes?

Answer 2

Enzymes are biological catalysts.
They increase the rate of reactions.
Without being chemically used / changed.

Question 3

Why are enzymes necessary in animals?

Answer 3

They catalyse thousands of biochemical reactions every second, (metabolic reactions) that control human processes.

Question 4

What does the enzyme do to the activation energy required to trigger the reaction?

Answer 4

Enzymes lower the activation energy required for a reaction to take place.

Question 5

Suggest the optimum temperature for enzyme-controlled reactions in humans:

Answer 5

37*C. (body temp.)

Question 6

A significant increase in temp above the optimum temp has an effect on enzyme-controlled reactions.
Explain why this is so:

Answer 6

• Increase causes denaturation due to broken bonds.
• Changed structure due to loss of 3* structure.
• Structural change causes functional change (3* = function).
• No longer catalyse reaction and rate decreases.

Question 7

State the word that best describes a region on the surface of an enzyme molecule where a substrate can bind.

Answer 7

Active site.

Question 8

State the word that best describes the energy required for a chemical reaction to take place.

Answer 8

Activation energy.

Question 9

What does an oxireductase do?

Answer 9

Catalyses redox reactions, through the transfer of hydrogen, oxygen or electrons.

Question 10

What does a transferase do?

Answer 10

Catalyses the transfer of a group from one compound to another, the process of transamination.

Question 11

What does a hydrolase do?

Answer 11

Catalyses hydrolysis and condensation reactions.

Question 12

What does a lysase do?

Answer 12

Catalyses the addition of a group across a double bond.

Question 13

What does a isomerase do?

Answer 13

Catalyses the rearrangements in a molecule to convert isomers.

Question 14

What does a ligase do?

Answer 14

Catalyses bond formation between compounds, using energy from the hydrolysis of ATP.

Question 15

What is produced when the enzyme lactase is added to milk?

Answer 15

Glucose and Galactose.

Question 16

What contributes to the structure of an enzyme?

Answer 16

The sequence of amino acids linked by peptide bonds.

Question 17

What does an increase in temp do to the movement of molecules?

Answer 17

Increases movement.

Question 18

What does an increase in temp do to the chance of collision between enyzme and substrate?

Answer 18

Increases chance of collision.

Question 19

What term is defined as:

A structural change of a protein that results in the loss of its biological properties.

Answer 19

Denaturation.

Question 20

How does an enzyme speed up the rate of reaction?

Answer 20

Provides an alternative reaction pathway with lower activation energy.

Question 21

When high temps denature a protein, what happens to its structure?

Answer 21

The hydrogen bonds and london forces between R groups have been broken leading to a change in the 3* structure.

Question 22

Casein can be used to test enzyme rates of hydrolysis, what feature allows this to be tested?

Answer 22

Casein changed colour when digested from an opaque white to clear.

Question 23

Are enzymes globular or fibrous?

Answer 23

Globular.

Question 24

What is the main role of enzymes?

Answer 24

Catalysing metabolic reactions, he making and breaking of bonds.

Question 25

What does a catalyst do to the ΔH (Enthalpy Change)?

Answer 25

Has no effect on ΔH

Question 26

What does a catalyst do the activation energy?

Answer 26

Lowers energy required.

Question 27

What are the two theories of enzyme action?

Answer 27

- Lock and key mechanism. | - Induced fit hypothesis.

Question 28

What is the lock and key hypothesis?

Answer 28

- The shape and charge of the substrate are complimentary to the active site. - They collide and bind to form an enzyme-substrate complex (e.s.c). - Products released, freeing the active site for the next reaction.

Question 29

What is the induced fit hypothesis?

Answer 29

- The collision between substrate and active site changes the shape of the enzyme slightly. - This creates strain on enzyme structure creating stored energy. - The recoil of the enzyme puts strain on the substrate, forming/breaking bonds. - Products released no longer fit the A.S.

Question 30

Name some factors that affect enzyme activity:

Answer 30

- Temperature; - pH; - Enzyme / Substrate concentration; - Inhibitors; - Co-factors or prosthetic groups.

Question 31

What is Q10?

Answer 31

The factor which rate of reaction increases for every 10*C rise in temp.

Question 32

What is the Q10 equation?

Answer 32

Rt x Q10 = Rt + 10

Question 33

Why does the stomach have a low pH?

Answer 33

To kill bacteria in food.

Question 34

Do all enzymes have the same optimum pH?

Answer 34

No they are all different.

Question 35

Explain the effects of increasing conc^ of substrate on frequency of collisions.

Answer 35

- Increasing conc^ increases the frequency of collisions as there are more substrates per area. - Until all active sites are occupied. - Then further increases have no effect on the frequency of collisions as they are not thee limiting factor.

Question 36

What is Vmax?

Answer 36

The maximum rate of reaction.

Question 37

How is Km found?

Answer 37

Half Vmax.

Question 38

What is Km?

Answer 38

The conc^ of substrate required to achieve half of Vmax.

Question 39

Explain the effect of increasing enzyme conc^ on rate of reaction.

Answer 39

Increased enzyme conc^ means more A.S available, more A.S means more collisions, this leads to more ESC formed.

Question 40

What are the two types of inhibition?

Answer 40

Competitive and Non-competitive.

Question 41

How does non-competitive inhibition work?

Answer 41

- The inhibitor does not bind to the active site, it binds to another part of the enzyme, the allosteric site. - This changes the tertiary structure as the shape of the A.S is altered. - Fewer ESC can be formed.

Question 42

What is the allosteric site?

Answer 42

Where non-competitive inhibitors bind.

Question 43

Explain competitive inhibition:

Answer 43

- The inhibitor fits into the active site. - This forms an enzyme-inhibitor complex (EIC) - This means the active site is in use and therefore, no ESC's can be formed.

Question 44

What is end product inhibition used for?

Answer 44

Controlling metabolic rates.

Question 45

When an inhibitor is bound to the allosteric site, what happens to the active site:

Answer 45

The shape is changed and therefore cannot form ESC's.

Question 46

What is an EIC?

Answer 46

Enzyme-Inhibitor Complex

Question 47

What is an ESC?

Answer 47

Enzyme-Substrate Complex

Question 48

What is a prosthetic group an example of?

Answer 48

A coenzyme.

Question 49

In enzyme experiments, the rate of enzyme activity often gradually decreases. What is most likely to cause this decrease?

Answer 49

The substrate concentration decreases.

Question 50

What volume of solution is needed to make 15cm^3 of 0.3M lactose solution from a 1.5M stock solution?

Answer 50

3cm^3

Question 51

Why would we use an initial rate of reaction?

Answer 51

To show maximum rate with no limiting factors.

Question 52

Describe the induced-fit model of enzyme action.

Answer 52

- Before the reaction, active site is not complimentary to substrate. - The shape of active site changes as substrate binds to the active site. - Enzyme-substrate complex forms. - Distortion of bonds in substrate leads to reaction.