Chapter 4 Enzymes Flashcards

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1
Q

What are enzymes?

A

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.

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2
Q

What two reactions do enzymes help to catalyse?

A

Anabolic ( building up)
Catabolic (breaking down)

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3
Q

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

A

Temperature
pH
Pressure

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4
Q

How are enzymes able to catalyse biological reactions?

A

Each enzyme lowers the activation energy of the particular reaction

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5
Q

How is an enzyme structured?

A

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.

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6
Q

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

A

The Lock and key Hypothesis
Induced- Fit model

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7
Q

What does the Lock and Key hypothesis state?

A

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.

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8
Q

What is the Induced fit hypothesis?

A

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.

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9
Q

What is denaturation?

A

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.

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10
Q

What are the properties of an enzyme affected by?

A

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

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11
Q

What are intracellular enzymes?

A

Enzymes located within the cell.

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12
Q

What is an example of an intracellular enzyme?

A

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

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13
Q

What are extra cellular enzymes?

A

Enzymes which work outside the cell.

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14
Q

What are examples of extra cellular enzymes?

A

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

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15
Q

How is starch broken down?

A

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.

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16
Q

How are proteins broken down?

A

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.

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17
Q

How does temperature affect enzyme activity?

A

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.

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18
Q

What is meant by temperature coefficient (Q10)?

A

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

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19
Q

What is the equation for temperature coefficient?

A

Q10= R2 / R1

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

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20
Q

How do enzymes denature from temperature?

A

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.

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21
Q

What is the optimum temperature?

A

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

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22
Q

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

A

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.

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23
Q

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

A

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

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24
Q

How can enzymes adapted to cold environments?

A

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.

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25
Q

How can enzymes be adapted to hot environments?

A

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.

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26
Q

What does the optimum pH mean for any particular enzyme?

A

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.

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27
Q

What does a change in pH refer to?

A

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.

28
Q

What is the process of renaturation?

A

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.

29
Q

How does pH cause the dénaturation of an enzyme?

A

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

30
Q

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

A

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

31
Q

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

A

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

32
Q

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

A

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.

33
Q

What factors affect enzyme activity?

A

Temperature
pH
Substrate and enzyme concentration

34
Q

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

A

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.

35
Q

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

A

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.

36
Q

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

A

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.

37
Q

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

A

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?

38
Q

What is a limiting factor?

A

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

39
Q

Why do enzymes need to be degraded?

A

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.

40
Q

What are enzyme inhibitors?

A

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

41
Q

What are the two types of enzyme inhibitors?

A

Competitive and Non-Competitive inhibitors

42
Q

What are competitive inhibitors?

A

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.

43
Q

How does competitive inhibitors reduce the rate of reaction?

A

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.

44
Q

What are Non-competitive inhibitors?

A

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.

45
Q

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

A

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.

46
Q

What is v max?

A

The highest rate of reaction.

47
Q

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

A

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.

48
Q

What is te difference between reversible and irreversible inhibitors?

A

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.

49
Q

What is end product inhibition?

A

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.

50
Q

What is end product inhibition an example of?

A

Non-competitive reversible inhibition

51
Q

What are cofactors?

A

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

52
Q

How are cofactors obtained?

A

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

53
Q

What is the cofactor of amylase?

A

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

54
Q

What are coenzymes?

A

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

55
Q

How are coenzymes obtained?

A

Many coenzymes are derived from Vitamins, such as Vitamin B

56
Q

How do cofactors and coenzymes bind?

A

Bind loosely

57
Q

What are Prosthetic Groups?

A

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

58
Q

What is a holoenzyme?

A

Enzyme with a cofactor/ coenzyme or prosthetic group attached.

59
Q

What are inactive precursor enzymes?

A

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.

60
Q

How do Precursor Enzymes become activated?

A

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.

61
Q

What is an apoenzyme?

A

Before a cofactor is added to a precursor enzyme.

62
Q

What are Zymogens and Proenzymes?

A

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.

63
Q

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

A

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

64
Q

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

A

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

65
Q

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

A

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.