4 - Enzymes

Question 1

Define co-enzyme

Answer 1

A cofactor that is an organic molecule

Question 2

Define catabolic

Answer 2

Reactions that break down large molecules into small ones

Question 3

What 4 factors affect the rate of enzyme-controlled reactions?

Answer 3

• temperature
• pH
• enzyme conc
• substrate conc

Question 4

Explain how denaturing leads to a loss of enzyme function

Answer 4

• bonds holding the secondary and tertiary structure together are broken
• changes the precise shape of the enzyme and active site
• substrate no longer complimentary

Question 5

Describe how the induced fit model works

Answer 5

• substrate not initially complimentary to active site
• active site is flexible
• molds itself around substrate
• returns to original shape after

Question 6

What is an enzyme’s temperature coefficient?

Answer 6

Q10
How much the rate of reaction increases for a 10-degree rise in temperature
Usually around 2

Question 7

Define anabolic

Answer 7

Reactions that build large molecules from small monomers

Question 8

How are prosthetic groups a part of enzymes? Give an example

Answer 8

Bound permanently and are part of its structure

eg. Zn2+ part of carbonic anhydrase in RBCs

Question 9

How do coenzymes work? Give an example.

Answer 9

Bind temporarily to enzyme, transfer chemical groups in substrate
eg. vitamins

Question 10

How do ions act as cofactors for enzymes?Give an example.

Answer 10

Bind to allosteric site and ensure active site is the right shape
Cl- ions for amylase

Question 11

Explain how pH can affect the 3d structure of an enzyme

Answer 11

high conc of H+ ions interact with the charged/polar R groups and distorts the 3d shape

Question 12

Define cofactor

Answer 12

A non-protein molecule that is required for a molecule to function (by binding to allosteric site)

Question 13

Name an intracellular enzyme and its function

Answer 13

catalase

breaks down hydrogen peroxide into water and oxygen

Question 14

Give an example of an extracellular enzyme

Answer 14

Any digestive enzyme eg. salivary amylase, pepsin, maltase…

Question 15

Define intracellular with regards to enzymes

Answer 15

An enzyme that catalyses a reaction within the cell it is produced in

Question 16

Define extracellular with regards to enzymes

Answer 16

An enzyme that catalyses a reaction outside of the cell it is produced in

Question 17

Define substrate

Answer 17

A specific molecule which interacts with an enzyme, fits into the active site

Question 18

Define activation energy

Answer 18

The energy that needs to be supplied for a chemical reaction to start

Question 19

Define active site

Answer 19

A specific region of an enzyme that is complementary to the substrate molecule

Question 20

How do enzymes affect a reaction in terms of energy

Answer 20

They lower the activation energy therefore less energy has to be supplied to start the reaction

Question 21

What is Vmax

Answer 21

The maximum rate at which the enzyme catalyses a reaction

Question 22

Explain how increasing the temperature increase the rate of an enzyme controlled reaction?

Answer 22

As temp increases KE of enzyme and substrate increases
collide more frequently
more frequent successful collisions
more E-S complexes formed

Question 23

Explain how low temperatures affect the rate of an enzyme controlled reaction?

Answer 23

As temp decreases KE of enzyme and substrate decreases
collide less frequently
less frequent successful collisions
fewer E-S complexes formed

Question 24

Explain how very high temperatures affect the rate of an enzyme controlled reaction?

Answer 24

• High temperatures can put strain on the bonds holding the enzyme together as there is more kinetic energy moving them around etc.
• Bonds can distort and break
• substrate no longer complementary to active site
• enzyme not functional

Question 25

How do extreme pHs affect the rate of an enzyme controlled reaction?

Answer 25

At extreme pHs, high conc. of H+ and OH- ions disrupt and break bonds between amino acids Substrate no longer complementary to active site -enzyme not functional

Question 26

Describe the lock and key model

Answer 26

Enzyme complementary to active site of enzyme | fit together and temporary bonds form, forming an E-S complex

Question 27

State any assumptions the lock and key model makes

Answer 27

- enzyme is rigid and doesn't change at all | - substrate is perfectly complementary to shape of active site

Question 28

Describe how the induced fit model is different from the lock and key model

Answer 28

Substrate not initially complementary to the active site Active site flexible Moulds itself to the substrate Distorts the bonds in the substrate, lowering activation energy Returns to original shape after

Question 29

What would this graph look like: rate of reaction as substrate conc. changes?

Answer 29

Rate of reaction increases as substrate conc. increases and then plateaus as all active sites are saturated

Question 30

What would this graph look like: rate of reaction as enzyme conc. changes?

Answer 30

Rate of reaction increases as enzyme conc. increases and then plateaus as other limiting factors eg. substrate conc.

Question 31

What could your dependent variables be in an experiment to measure the rate of a reaction?

Answer 31

How quickly substrate used up | How quickly product formed

Question 32

How do competitive inhibitors work?

Answer 32

Similar shape to substrate | binds to active site so substrate can't

Question 33

How do competitive inhibitors affect the rate of reaction and why does this happen?

Answer 33

Rate of reaction for given substrate conc. decreases however the Vmax is still reached because there will eventually be considerably more substrate than inhibitor so it will not effect it

Question 34

Name 2 examples of competitive inhibitors and their roles

Answer 34

Statins- inhibit cholesterol production | Asprin - inhibit chemicals responsible for pains and fevers

Question 35

How do non-competitive inhibitors work?

Answer 35

Complimentary to allosteric site, creates a conformational change to the shape o the active site Substrate can't bind

Question 36

How do non-competitive inhibitors affect the rate of reaction and why does this happen?

Answer 36

Increasing substrate conc. will not overcome the inhibition, the graph would be lower (ROR slower) and plateaus beneath normal graph

Question 37

How do end product inhibitors work?

Answer 37

-end product acts as a negative feedback by inhibiting a previous step in its production, this prevents an accumulation of certain substances

Question 38

Enzymes that are not yet active are called

Answer 38

Apoenzymes

Question 39

Define apoenzyme

Answer 39

An enzyme that is not yet active

Question 40

Enzymes that have been activiated with the addition of a cofactor are called

Answer 40

Holoenzymes

Question 41

Define holoenzymes

Answer 41

Enzymes that have been activiated with the addition of a cofactor

Question 42

Why could precursor activation be necessary for enzymes?

Answer 42

The active enzyme could cause damage in one area so is only activated when it gets to its site

Question 43

Give an example of a precursor enzyme and why it is necessary for it to be activated somewhere else

Answer 43

Pepsin (hydrolyses proteins into amino acids) | could be dangerous in cells so it in secreted inactively

Question 44

Describe 2 ways cofactors are necessary for enzymes function

Answer 44

cofactors transfer groups between reactants | form part of the active site