Module 2: Enzymes

Question 1

What is an enzyme?
What do enzymes do?
How do they do this?

Answer 1

a biological catalyst

they catalyze metabolic reactions by providing a lower activation energy

they interact with substrate molecules causing them to react at faster rates

Question 2

Is an enzyme a fibrous , conjugated or globular protein?

Answer 2

a globular protein

Question 3

What is the difference between an intracellular and an extracellular enzyme?

Name 1 extracellular and 1 intracellular enzyme

Answer 3

intracellular-found in the cytoplasm/attached to cell membrane and they carry out their function within the cell they are produced in

extracellular-they are released from the cell producing them so carry out their function outside the cell

i-catalase
e-amylase

Question 4

Enzymes can only increase the rate of a chemical reaction to a certain point , what is this point known as?

Answer 4

the Vmax

Question 5

What is an anabolic reaction?

What is a catabolic reaction?

Answer 5

a reaction that builds up molecules into larger structures , they are all catalyzed by enzymes

a reaction that breaks down larger molecules , they are also catalyzed by enzymes

Question 6

What is activation energy?

What is meant by the term ‘enzyme specificity’

Answer 6

the energy required to start a chemical reaction

that each enzyme is specific to 1 reaction

Question 7

What is the active site of an enzyme?

Answer 7

an area within the enzymes tertiary structure that’s shape is complementary to a specific substrate molecule

Question 8

What are the 2 hypotheses for how enzymes help molecules collide successfully?

Answer 8

the lock and key hypothesis
the induced fit hypothesis

Question 9

Explain the lock and key hypothesis

What is it called when the enzyme and substrate bind together?

What is it called when products are produced?

Answer 9

an enzymes active site is complementary to only 1 specific substrate molecule so it will only bind with that specific substrate
-the substrate/substrates then react to form a product/products

-an enzyme substrate complex
-an enzyme product complex

Question 10

Explain the induced fit hypothesis

Answer 10

when the enzyme and the substrate bind to one another , structural changes to the enzyme take place so that the active site fits precisely around the substrate

-the initial interaction between the enzyme and substrate is relatively weak but they rapidly cause changes in the enzymes tertiary structure which strengthens the binding and strains the substrate molecule , causing some of its bonds to be broken which lowers the activation energy

Question 11

What does catalase do ?

Answer 11

ensures the breakdown of the toxic substance Hydrogen Peroxide into Oxygen and Water

Question 12

What four factors affect the rate of enzyme controlled reactions?

Answer 12

-pH
-substrate concentration
-enzyme concentration
-temperature

Question 13

What effect does pH have on enzyme controlled reactions?

Answer 13

the active site is only the right shape at a certain concentration of H+ ions so when pH changes the active site is altered but if pH returns to its optimum then the active site will return to its normal shape(Renaturation)

-more significant changes in pH irreversibly alter the active site(Denaturation)

Question 14

What do H+ ions interact with within enzymes?
What does this interaction cause?

Answer 14

the polar/charged R groups

-if H+ ions are interacting with R groups then the R groups can interact less with each other which causes bonds to break

Question 15

What effect does temperature have on enzyme controlled reactions?

Answer 15

-a temp increase increases the kinetic energy of particles meaning they move faster and collide more frequently

Question 16

If temperature is too high, what happens ?

Answer 16

the bonds holding the enzyme in its tertiary structure vibrate more and eventually break which causes a change in active site shape meaning its no longer complementary to its substrate(Denaturation)

Question 17

What is meant by a temperature coefficient(Q10)?

Answer 17

its the measure of how much the ROR increases with a 10 degree rise in temperature

Question 18

What effect does enzyme concentration have on enzyme controlled reactions?

Answer 18

the ROR increases as enzyme concentration increases as there are more active sites for substrates to bind to

increasing the enzyme concentration beyond a certain point has no effect on the ROR
as there are more active sites than substrates so substrate concentration becomes the
limiting factor

Question 19

What effect does substrate concentration have on enzyme controlled reactions?

Answer 19

as the concentration increases the ROR increases as there are more substrates available to bind with active sites
however this only increases to a certain point as eventually there will be no more active sites available so adding more substrate will have no effect on ROR

Question 20

What is an inhibitor?

Name the 2 types of inhibition

Answer 20

a substance which slows down or stops a reaction by affecting the binding of substrates to enzymes active sites

competitive and non-competitive

Question 21

Explain competitive inhibition
What does this do to the reaction?

Do competitive inhibitors bind permanently or temporarily?

Answer 21

-a molecule that has a similar shape to a substrate of an enzyme can fit and bind to the active site
-this blocks the substrate from binding to the active site which prevents the enzyme from catalysing the reaction and slows down the ROR
-the enzyme can’t carry out its function so is said to be inhibited
-the non substrate molecule and the substrate molecules in the solution will compete for the active sites

-most only bind temporarily so there effect is reversible

Question 22

Does competitive inhibition change the Vmax of the enzyme?
What can be done to overcome the effect of the competitive inhibitors?

Answer 22

no
if more substrate is added it will mean there is much more substrate then inhibitor so the likeliness of the substrate binding becomes greater , meaning the Vmax can still be reached

Question 23

Explain non-competitive inhibition , why is it called this?

Do non competitive inhibitors have a reversible/irreversible effect?

Answer 23

-the inhibitor molecule binds to the allosteric site of the enzyme instead of the active site
-this binding causes a change in the tertiary structure of the enzyme , resulting in the active site changing shape
-this means the active site is no longer complementary to the substrate molecules and form any product
-its called non-competitive because the inhibitor and substrate aren’t competing for the active site

-they have an irreversible effect

Question 24

Would increasing the substrate/enzyme concentration have any effect on non competitive inhibition , if not then why?

Answer 24

No , because even at high substrate concentration there won’t be more binding as they are no longer complementary to the enzyme and increasing enzyme concentration will have no effect because they will just be changed

Question 25

What is meant by end-product inhibition?

Answer 25

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

Question 26

What kind of feedback is end-product inhibition known as?

What does this type of inhibition prevent?

Answer 26

negative feedback

prevents excess products being made and wasting resources

Question 27

What is a co-factor?
What can they do?

Answer 27

a non protein compound required for the enzymes activity to occur
transfer atoms or groups from one reaction to another in a multi step pathway
they can also form part of the enzymes active site

Question 28

What are the 3 types of cofactors?

Answer 28

co-enzymes , activators and prosthetic groups

Question 29

What is a co-enzyme and what does it do ?

How are they obtained?

How does a chloride ion act as a cofactor for amylase?

Answer 29

its an organic cofactor which doesn’t bind permanently , they facilitate the binding of substrate to the active site

obtained through the diet as minerals

it is necessary for the correct formation of amylase’s active sites

Question 30

Where else can co-enzymes be derived from?

Answer 30

vitamins

Question 31

What do prosthetic groups do in terms of binding?

Answer 31

they bind tightly to the enzyme and form a permanent feature of the protein

Question 32

What is a precursor enzyme?
What is the name for the innactive and active form of them?
What is often used to change the enzymes shape and activate it?

Answer 32

an innactive enzyme that often needs to change shape to be activated
innactive-apoenzyme
active-holoenzyme
a cofactor

Question 33

What is the difference between an inorganic and an organic cofactor?
make 3 points for organic

Answer 33

organic-participate in the reaction and are changed by it , they are continually recycled during the process
they often act as carriers by moving chemical groups between enzymes

inorganic-help enzyme and substrate bind but don’t directly participate in the reaction so aren’t used up or changed