Unit 4 - Enzymes

Question 1

What are enzymes?

Answer 1

Biological catalysts made of proteins which interact with substrate molecules causing them to react at high rates.

Question 2

Why are enzymes important?

Answer 2

Without enzymes, reactions would need extremely high temperatures and pressures to take place at the rates needed. This would damage the cell components.

Question 3

What is the structure of enzymes?

Answer 3

Enzymes are globular proteins (they have a 3D, spherical shape) with a specific tertiary structure. They contain an active site with a specific shape that binds to the substrate molecule.

Question 4

Are enzymes soluble in water?

Answer 4

Enzymes are soluble in water due to the position of the hydrophilic and hydrophobic R groups.

Question 5

Define activation energy.

Answer 5

The activation energy for a reaction is the minimum amount of energy required for the reaction to take place.

Question 6

Define anabolic enzyme.

Answer 6

An anabolic enzyme builds molecules.

Question 7

Define catabolic enzyme.

Answer 7

A catabolic enzyme breaks down molecules.

Question 8

How do anabolic enzymes lower the activation energy?

Answer 8

When the two substrate molecules fit into the active site, the enzyme holds them together so they can bond more easily.

Question 9

How do catabolic enzymes lower the activation energy?

Answer 9

Fitting into the active site causes a strain on the bonds of the substrate, allowing them to break more easily.

Question 10

Define intracellular enzyme.

Answer 10

Intracellular enzymes work inside cells.

Question 11

Define extracellular enzyme.

Answer 11

Extracellular enzymes work outside of cells - they break down large polymers to release nutrients for the cell.

Question 12

What does amylase do and where is it produced?

Answer 12

Amylase catalyses the breakdown of starch to maltose. It is produced by the salivary glands and pancreas.

Question 13

What does maltase do and where is it found?

Answer 13

Maltase catalyses the breakdown of maltose into glucose. It is found in the small intestine.

Question 14

What does trypsin do and where is it produced?

Answer 14

Trypsin catalyses the breakdown of proteins into smaller peptides. It is produced in the pancreas and secreted into the small intestine.

Question 15

What is the lock and key theory for how enzymes work?

Answer 15

In the lock and key theory, the shapes of the substrate and active site are complementary. The substrate fits into the active site, which catalyses the reaction, and the products are released, leaving the enzyme free to bind to another substrate.

Question 16

What is the induced-fit theory for how enzymes work?

Answer 16

In the induced-fit theory, the shapes of the substrate and active site are roughly complementary, and when they interact the tertiary structure of the enzyme changes. This strengthens the binding between the active site and the substrate, allowing a closer fit and catalysing the reaction.

Question 17

Why does the rate of reaction increase as the temperature increases (before the optimum temperature?

Answer 17

As the temperature increases, the particles gain kinetic energy, allowing more enzyme-substrate complexes to form.

Question 18

Why does the rate of reaction decrease when the temperature increases beyond the optimum temperature?

Answer 18

The high temperatures cause the enzyme molecules to vibrate rapidly, disrupting the tertiary structure of the enzyme. This changes the shape of the active site, denaturing the enzyme and preventing enzyme-substrate complexes from forming.

Question 19

What is the Q10 value for a reaction?

Answer 19

How much the rate of reaction changes when hte temperature is raised by 10C.

Question 20

How do you calculate the Q10 for a reaction?

Answer 20

Q10 = rate at higher temperature / rate at lower temperature

Question 21

What does a change in pH mean?

Answer 21

A change in hydrogen ion concentration.

Question 22

Why does the structure of the enzyme change at a different pH to the optimum?

Answer 22

The hydrogen and ionic bonds between R groups that hold the enzyme’s shape together will react with hydrogen ions.

Question 23

What happens if the pH returns to optimum quickly enough?

Answer 23

Renaturation will occur - the active site will return to its original shape.

Question 24

What happens if the pH changes significantly from the optimum?

Answer 24

The enzyme will be fully denatured and unable to return to its original shape.

Question 25

Why does a lower pH than optimum change the enzyme’s shape?

Answer 25

The R groups will react with the hydrogen ions and therefore interact less with each other. This breaks bonds, changing enzyme shape.

Question 26

Why does a higher pH than optimum change the enzyme’s shape?

Answer 26

The R groups will interact more with each other because there are less hydrogen ions.

Question 27

Why does increasing enzyme concentration increase the rate of reaction only up to a point before plateauing?

Answer 27

Initially, an increase in enzyme concentration will increase the amount of active sites in an area, leading to more enzyme-substrate complexes forming. However, after a point, all the substrate molecules will be occupied and increasing enzyme concentration will have no effect.

Question 28

Why does increasing substrate concentration increase the rate of reaction only up to a point before plateauing?

Answer 28

Initially, an increase in substrate concentration will increase the amount of collisions in an area, leading to more enzyme-substrate complexes forming. However, after a point, all the active sites will be occupied and increasing substrate concentration will have no effect.

Question 29

What is the V max for a reaction?

Answer 29

The V max is the maximum rate of reaction, or the point at which all active sites have formed enzyme-substrate complexes and no more can form until an active site becomes available.

Question 30

What are inhibitors?

Answer 30

Inhibitors are molecules which decrease the rate of reaction by preventing enzymes from catalysing reactions.

Question 31

What are competitive inhibitors and how do they decrease the rate of reaction?

Answer 31

Competitive inhibitors have a complementary shape to the active site and bind to it, blocking the substrate from forming an enzyme-substrate complex. This reduces the amount of catalysis for the reaction and therefore the rate.

Question 32

Do competitive inhibitors affect the V max?

Answer 32

Competitive inhibitors do not change the V max, but they increase the time taken for the reaction to reach V max.

Question 33

Can the effect of competitive inhibitors be reversed?

Answer 33

Yes.

Question 34

What are non-competitive inhibitors and how do they decrease the rate of reaction?

Answer 34

Non-competitive inhibitors bind to the enzyme’s allosteric site (different to active site), changing the shape of the active site. This means the substrate is no longer complementary and can’t form an enzyme-substrate complex.

Question 35

What effect do non-competitive inhibitors have on the V max?

Answer 35

Non-competitive inhibitors can decrease the V max as well as reducing time taken to reach V max (but it doesn’t always).

Question 36

Is the effect of non-competitive inhibitors reversible?

Answer 36

It can be reversible or non-reversible - non-reversible inhibitors cannot be removed from the allosteric site.

Question 37

Do competitive or non-competitive inhibitors have a stronger effect on the rate of reaction?

Answer 37

Non-competitive inhibitors decrease the reaction further than competitive inhibitors.

Question 38

What is end-product inhibition?

Answer 38

End-product inhibition is when the product of a reaction acts as an inhibitor to the enzyme that produced it.

Question 39

Is end-product inhibition reversible?

Answer 39

Yes.

Question 40

What enzyme does copper sulphate inhibit and is it a competitive, non-competitive or end-product inhibitor?

Answer 40

Copper sulphate inhibits catalase, which catalyses the breakdown of hydrogen peroxide. It is a non-competitive inhibitor.

Question 41

What enzyme do statins inhibit and are they a competitive, non-competitive or end-product inhibitor?

Answer 41

Statins inhibit an enzyme which synthesises cholesterol - helping prevent heart disease. They are competitive inhibitors.

Question 42

What enzyme do malonate and oxaloacetate inhibit and are they competitive, non-competitive or end-product inhibitors?

Answer 42

Malonate and oxaloacetate inhibit succinate dehydrogenase, which works on the substrate succinate in respiration. They are competitive inhibitors.

Question 43

What enzyme does ATP inhibit and is it a competitive, non-competitive or end-product inhibitor?

Answer 43

ATP inhibits phosphofructokinase (PFK), which catalyses the first step of respiration. ATP is an end-product inhibitor.

Question 44

What enzyme do organophosphates inhibit and are they a competitive, non-competitive or end-product inhibitor?

Answer 44

Organophosphates inhibit acetyl cholinesterase, which is essential for nerve impulse transmission. They are non-competitive inhibitors.

Question 45

What enzyme do proton pump inhibitors inhibit and are they a competitive, non-competitive or end-product inhibitor?

Answer 45

Proton pump inhibitors inhibit an enzyme that secretes hydrogen ions into the stomach. They help treat long-term indigestion and are non-competitive inhibitors.

Question 46

What enzymes does aspirin inhibit and is it a competitive, non-competitive or end-product inhibitor?

Answer 46

Aspirin irreversibly inhibits COX enzymes, which synthesise chemicals that produce pain and fever. It is a competitive inhibitor.

Question 47

What is a cofactor?

Answer 47

A non-protein component which is bound to an enzyme to help with the enzyme’s function.

Question 48

What is an inorganic cofactor?

Answer 48

A cofactor obtained from the diet via minerals, which does not directly participate in the reaction.

Question 49

Are inorganic cofactors used up or changed in the reaction?

Answer 49

No

Question 50

How do inorganic cofactors help enzymes catalyse reactions?

Answer 50

They alter the charge of the active site, allowing the enzyme-substrate complex to form.

Question 51

Give an example of an enzyme that needs an inorganic cofactor to function.

Answer 51

Either:
Amylase - chloride ion
Catalase - iron ions

Question 52

What are organic cofactors called?

Answer 52

Coenzymes.

Question 53

What is a coenzyme?

Answer 53

A cofactor obtained from the diet as vitamins, which is not permanently bound to the enzyme but may be temporarily or loosely bound to the enzyme.

Question 54

Are coenzymes changed or used up in the reaction?

Answer 54

Coenzymes are changed, but are then recycled so they can take part in the reaction again.

Question 55

Give an example of a coenzyme.

Answer 55

Either:
NAD (respiration) - from Vitamin B3
NADP (photosynthesis) - from Vitamin B3
A (respiration) - from Vitamin B5

Question 56

What are precursor enzymes?

Answer 56

Enzymes produced in an inactive form which must be activated before they can start catalysing reactions.

Question 57

Why are some enzymes produced as precursor enzymes?

Answer 57

Because they can cause damage to the cells and tissues where they are produced. Alternatively, because the reaction must be controlled or happen only under certain conditions.

Question 58

How does a cofactor activate a precursor enzyme?

Answer 58

By changing the tertiary structure, which changes the shape of the active site so that the enzyme can form the enzyme-substrate complex.

Question 59

What ways can a precursor enzyme be activated besides the addition of a cofactor?

Answer 59

Another enzyme can be used to break bonds in the enzyme, changing the shape of the active site. Another way is if the conditions such as temperature or pH change.

Question 60

What is a precursor enzyme called when it is inactive?

Answer 60

An apoenzyme.

Question 61

What is a precursor enzyme called when it has been activated?

Answer 61

A holoenzyme.

Question 62

What is a precursor enzyme which is activated by a change in the conditions called?

Answer 62

A zymogen or a proenzyme.

Question 63

Give an example of a proenzyme.

Answer 63

Pepsin is produced as the inactive form pepsinogen, which is activated by the acid pH in the stomach. This protects the tissues in the body from being digested by pepsin.

Question 64

What is a prosthetic group?

Answer 64

A cofactor which is tightly bound to an enzyme.

Question 65

Give an example of an enzyme with a prosthetic group.

Answer 65

Carbonic anhydrase is an enzyme necessary for the metabolism of carbon dioxide which contains zinc ions.