Chapter 4 Enzymes

Question 1

What are enzymes?

Answer 1

Enzymes are biological catalysts. They are globular proteins which bind with substrate molecules causing them to react at faster rates without the need for harsh environments.

Question 2

What two reactions do enzymes help to catalyse?

Answer 2

Anabolic ( building up)
Catabolic (breaking down)

Question 3

What environmental factors can affect the rate of a chemical reaction?

Answer 3

Temperature
pH
Pressure

Question 4

How are enzymes able to catalyse biological reactions?

Answer 4

Each enzyme lowers the activation energy of the particular reaction

Question 5

How is an enzyme structured?

Answer 5

An enzyme has a tertiary structure which folds a sequence of amino acids into a precise 3D shape. A region within the tertiary structure is complementary to the shape of a specific substrate molecule, called the active site.

Question 6

What are the two hypothesises that explain how enzymes catalyse reactions?

Answer 6

The Lock and key Hypothesis
Induced- Fit model

Question 7

What does the Lock and Key hypothesis state?

Answer 7

The active site of an enzyme is a specific shape to fit a complementary substrate. When there has been a successful collision between the enzyme and the substrate, the substrate will bind to the active site an enzyme-substrate complex is formed. The substrate will then react and the products formed are known as the enzyme-product complex. Finally, the products are released leaving the active site unchanged.

Question 8

What is the Induced fit hypothesis?

Answer 8

The complementary shape of the active site and the substrate allows them to bind together during a successful collision.Therefore, the presence of the substrate induces a change within the active site to the shape of the R-groups of the amino acids. An enzyme-substrate complex is then formed which strengthens binding. Once the substrate has been converted into its product(s), an enzyme-product complex will be formed. Finally, the different shape of the product (compared to the substrate) allows the molecules to detach from the active site and move away. The enzyme is then free to catalyse another reaction with the same type of substrate.

Question 9

What is denaturation?

Answer 9

This is where external factors, such as an increase in temperature or change in pH, can disrupt the tertiary structure bond and irreversibly change the shape of the active site.

Question 10

What are the properties of an enzyme affected by?

Answer 10

The tertiary structure of the enzymes active site and its ability to combine with a complementary substrate.

Question 11

What are intracellular enzymes?

Answer 11

Enzymes located within the cell.

Question 12

What is an example of an intracellular enzyme?

Answer 12

Catalase
Enzyme which breaks down the toxic hydrogen peroxide into oxygen and water preventing its accumulation.

Question 13

What are extra cellular enzymes?

Answer 13

Enzymes which work outside the cell.

Question 14

What are examples of extra cellular enzymes?

Answer 14

Amylase is a carbohydrase enzyme which catalyses the hydrolysis of 1-4 glycosidic bonds found in starch.
Maltase is also a carbohydrase enzyme which catalyses the breakdown of maltose.
Trypsin is a protease enzyme which catalyses the breakdown of proteins into amino acids
Pepsin also is a protease enzyme which catalyses the breakdown of proteins into amino acids

Question 15

How is starch broken down?

Answer 15

Starch polymers are partially broken down into maltose by the enzyme amylase. Amylase is found within the salivary glands and the small intestine.
Maltose is then broken down into glucose by the enzyme maltase which is present in the small intestine.

Question 16

How are proteins broken down?

Answer 16

Proteins are broken down by protease enzymes such as Trypsin, which catalyses the digestion of proteins into smaller peptides which can then be broken down into amino acids by other protease enzymes. Trypsin is produced in the pancreas and released into the small intestine.

Question 17

How does temperature affect enzyme activity?

Answer 17

Increasing the temperature increases the rate of the enzyme-controlled reaction. This is due to the increased kinetic energy within the enzyme and substrate molecules so more frequent successful, effective collisions can take place between the complementary molecules. Consequently, this increases the rate of formation of enzyme-substrate complexes and therefore the rate of enzyme-product complexes produced per second.

Question 18

What is meant by temperature coefficient (Q10)?

Answer 18

Temperature coefficient describes the increase in temperature rate of reaction as a result of increasing the temperature by 10 degrees.

Question 19

What is the equation for temperature coefficient?

Answer 19

Q10= R2 / R1

R1= represents the rate of reaction at x degrees
R2= represents the rate of reaction at
(x + 10 degrees)

Question 20

How do enzymes denature from temperature?

Answer 20

Increasing temperature above the optimum causes the bond holding the protein together in the enzyme molecule to vibrate more vigorously and eventually break. This therefore results in a disruption to the precise tertiary structure of the protein and a change to the shape of the active site. This means that now the enzyme is no longer complementary to the substrate- it has become denatured.

Question 21

What is the optimum temperature?

Answer 21

The optimum temperature is at which the enzyme has the highest rate of activity. The optimum temperatures of enzymes can vary.

Question 22

How does the rate of reaction change if an enzyme is above its optimum temperature?

Answer 22

The rate of reaction above optimum temperature decreases rapidly because the active site has irreversibly changed and the enzyme has denatured.Consequently, this means that the active site and substrate are no longer complementary so the rate of reaction is zero.

Question 23

How does the rate of reaction change if an enzyme is below its optimum temperature?

Answer 23

The rate of reaction decreases less rapidly below optimum temperature because the enzymes have not denatured, they are just less active.

Question 24

How can enzymes adapted to cold environments?

Answer 24

Enzymes adapted to the cold tend to have more flexible structures, particularly at the active site. However, this generally makes them less stable and more likely to denature due to small temperature changes.

Question 25

How can enzymes be adapted to hot environments?

Answer 25

Enzymes are more stable as there is an increased number of bonds, particularly hydrogen bonds and disulphide bridges , in its tertiary structure. Therefore, the shapes of the active site is more resistant to changes in temperature.

Question 26

What does the optimum pH mean for any particular enzyme?

Answer 26

The optimum pH is where the rate of an enzyme-controlled reaction is quickest, because the active site has a precise shape which is complementary to a specific substrate at a certain hydrogen ion concentration.

Question 27

What does a change in pH refer to?

Answer 27

A change in pH refers to a change in the hydrogen ion concentration. More hydrogen ions are present in a low pH (acidic) environments while fewer hydrogen ions are present in high pH (alkaline) environments.

Question 28

What is the process of renaturation?

Answer 28

When the pH changes from the optimum of an enzyme, the tertiary structure of an enzyme is affected and therefore the shape of the active site is altered. However, if the pH returns to the optimum then the protein will resume its original shape and catalyse the reaction again.

Question 29

How does pH cause the dénaturation of an enzyme?

Answer 29

When the pH changes more significantly, the structure of the enzyme becomes irreversibly altered so the active site is no longer complementary to the substrate and the rate of reaction is reduced. This is because the concentration of hydrogen ions (H+) affects the interactions between the R-groups, which eventually breaks

Question 30

What enzyme(s) acts within the saliva and at what pH?

Answer 30

Amylase is found within the saliva and takes action within the mouth/throat and works at a pH 7-8 .

Question 31

What enzyme(s) acts in the Gastric Juice and at what pH?

Answer 31

Pepsin is found in the Gastric Juice which takes action in the Stomach and functions at an acidic pH of 1-2

Question 32

What enzyme(s) acts in the Pancreatic Juice and at what pH?

Answer 32

Trypsin, Lipase, Amylase and Maltase are all found in the Pancreatic Juice found which takes action in the Small intestine. These enzymes work at a slightly alkaline pH of 8.

Question 33

What factors affect enzyme activity?

Answer 33

Temperature
pH
Substrate and enzyme concentration

Question 34

What is the effect of substrate concentration on the rate of an enzyme-controlled reaction?

Answer 34

When the concentration of a substrate increases, this means that there are more substrate molecules in a given volume. Consequently, this leads an increased rate of reaction as more frequent, effective collisions can take place between the enzymes and substrates so there is a higher number of enzyme-substrate complexes formed and subsequently more products produced per second.

Question 35

What is the effect of enzyme concentration on the rate of an enzyme-controlled reaction?

Answer 35

As enzyme concentration increases, there is a greater availability of active sites in a given volume, which when effective collisions occur will be occupied by substrates. This means that more enzyme- substrate complexes can form and more products will be produced per second, increasing the rate of reaction.

Question 36

What is the limiting factor when substrate concentration reaches its maximum rate?

Answer 36

Despite the increase in substrate concentration, the rate of reaction is at its maximum because all of the active sites have become saturated so the number of active sites available/ enzyme concentration has become the limiting factor. Therefore no more enzyme-substrate complexes can form unless the concentration of enzymes is increased.

Question 37

What is the limiting factor when enzyme concentration reaches its maximum rate and how does this change when the enzyme concentration is increased?

Answer 37

Before the rate of reaction reaches its maximum, the limiting factor is the enzyme concentration. However, if the enzyme concentration is increased further then there will be no increase in the rate of reaction. This is because the active sites of the extra enzyme molecules will not be occupied by substrates, so the substrate concentration will become the limiting factor?

Question 38

What is a limiting factor?

Answer 38

A factor, when in short supply, will prevent the enzyme-controlled reaction from occuring at its maximum rate.

Question 39

Why do enzymes need to be degraded?

Answer 39

Enzymes may need to be degraded because some enzymes can be abnormally shaped, therefore this prevents them from accumulating and potentially harming the cell. Additionally, any enzymes that are in excess and not essential for the functioning of the cell at that particular moment will also be degraded.

Question 40

What are enzyme inhibitors?

Answer 40

Inhibitors are molecules which prevent enzymes from carrying out their normal function as catalysts or slow them down.

Question 41

What are the two types of enzyme inhibitors?

Answer 41

Competitive and Non-Competitive inhibitors

Question 42

What are competitive inhibitors?

Answer 42

A molecule which has a similar shape to the substrate is able to fit into the active site of the enzyme. This therefore blocks the substrate from entering the active site preventing it from catalysing the reaction. Most competitive inhibitors only bind temporarily to the active site, so their effect is reversible.

Question 43

How does competitive inhibitors reduce the rate of reaction?

Answer 43

Substrate and inhibitor molecules will compete with each other to bind to active sites of the enzymes, this reduces the number of substrate molecules binding to the active site at any one time slowing the rate of the reaction.

Question 44

What are Non-competitive inhibitors?

Answer 44

The inhibitor will bind to the enzyme in a location other than the active site- known as the allosteric site.
This binding of the inhibitor therefore causes the tertiary structure of the enzyme to change, meaning the active site also changes shape.
This result in the active site no longer having a complementary substrate as it is unable to bind.

Question 45

Why don’t competitive inhibitors change the v max of an enzyme?

Answer 45

Competitive inhibitors can reduce the rate of reaction, but cannot change the v max of the enzyme it inhibits. This is because increasing substrate concentration ‘dilutes’ the inhibitor, therefore making it more likely that the substrate will collide with the active site than the inhibitor. Consequently, the v max of an enzyme can still be reached if there is enough substrate.

Question 46

What is v max?

Answer 46

The highest rate of reaction.

Question 47

Why do Non-competitive inhibitors change the v max of an enzyme?

Answer 47

The reaction is not increased by increasing the substrate because the active site has changed shape , therefore the v max cannot be reached even if there is a greater substrate concentration.

Question 48

What is te difference between reversible and irreversible inhibitors?

Answer 48

Irreversible inhibitors cannot be removed from part of the enzyme they are attached to, while reversible inhibitors are temporary and can be detached from the enzyme.

Question 49

What is end product inhibition?

Answer 49

Enzyme inhibition that occurs when the product of a a reaction acts as an inhibitor to the enzyme that produces it. This serves as a negative feedback control mechanism for the reaction, so excess products are not made.

Question 50

What is end product inhibition an example of?

Answer 50

Non-competitive reversible inhibition

Question 51

What are cofactors?

Answer 51

Non proteins (inorganic) components that are necessary for the effective functioning of an enzyme

Question 52

How are cofactors obtained?

Answer 52

Inorganic cofactors are obtained from the diet as minerals such as Iron, Zinc, Calcium and Chloride ions

Question 53

What is the cofactor of amylase?

Answer 53

Cl- is the cofactor of amylase which catalyses the breakdown of starch helping the substrate to bind easier.

Question 54

What are coenzymes?

Answer 54

Organic components (containing carbon) that are necessary for the effective functioning of an enzyme

Question 55

How are coenzymes obtained?

Answer 55

Many coenzymes are derived from Vitamins, such as Vitamin B

Question 56

How do cofactors and coenzymes bind?

Answer 56

Bind loosely

Question 57

What are Prosthetic Groups?

Answer 57

Can be coenzymes or cofactors which bind tightly to the enzyme.
For example, Zn2+ is the prosthetic group for Carbonic anhydrase

Question 58

What is a holoenzyme?

Answer 58

Enzyme with a cofactor/ coenzyme or prosthetic group attached.

Question 59

What are inactive precursor enzymes?

Answer 59

Enzymes that are produced in an inactive form. Particularly enzymes that can cause damage within the cells producing them or to tissues where they are released or enzyme whose action needs to e controlled.

Question 60

How do Precursor Enzymes become activated?

Answer 60

To become activated, precursor enzymes need to undergo a change in shape (tertiary structure) to the active site. This can be achieved by adding a cofactor.

Question 61

What is an apoenzyme?

Answer 61

Before a cofactor is added to a precursor enzyme.

Question 62

What are Zymogens and Proenzymes?

Answer 62

Precursor enzymes which have been activated by either the influence of another enzyme or a change in conditions such as temperature of pH. Consequently, activating the enzyme because the tertiary structure changes.

Question 63

How do enzymes catalyse a reaction according to the Lock and Key Hypothesis?

Answer 63

The charged groups within the active site distort the substrate lowering the activation energy

Question 64

How do enzymes catalyse a reaction according to the Induced Fit Model?

Answer 64

When an enzyme-substrate complex is formed, it puts strain on the bonds lowering the activation energy.

Question 65

Some enzymes work better in the presence of other molecules or ions.
Explain how these molecules or ions increase the activity of enzymes

Answer 65

The attached prosthetic groups, co-enzymes, cofactors bind to the enzyme which induce the active site to change its shape as the tertiary structure has been altered.
This means there are more successful collisions and so more enzyme-substrate complexes are formed meaning the rate of reaction is greater.