4 Enzymes

Question 1

What are enzymes?

Answer 1

Enzymes are biological catalysts that interact with substrate molecules to facilitate chemical reactions.

Question 2

What is anabolism?

Answer 2

Reactions of metabolism that construct molecules from smaller units.

Question 3

What is catabolism?

Answer 3

Reactions of metabolism that break molecules down into smaller units.

Question 4

What type of reaction is needed for growth?

Answer 4

Anabolic reaction.

Question 5

An example of an intracellular enzyme.

Answer 5

Catalase is an enzyme that works inside cells to catalyse the breakdown of hydrogen peroxide to harmless oxygen and water. Hydrogen peroxide is the toxic by-product of several cellular reactions. If left built up, it can kill cells.

Question 6

Examples of extracellular enzymes.

Answer 6

Amylase and trypsin.

Question 7

How do the extracellular enzymes work to digest starch?

Answer 7

1) Starch polymers are partially broken down into maltose (a disaccharide) by amylase. Amylase is produced by the salivary glands and the pancreas. It is released in saliva into the mouth, and in pancreatic juice into the small intestine.
2) Maltose is then broken down into glucose (a monosaccharide) by maltase. Maltase is present in the small intestine.
- Glucose is small enough to be absorbed by the cells lining the digestive system and then absorbed into the bloodstream.

Question 8

How do the extracellular enzymes work to digest proteins?

Answer 8

• Trypsin is a protease, a type of enzyme that catalyses the digestion of proteins into smaller peptides, which can then be broken down further into amino acids by other proteases.
• Trypsin is produced in the pancreas and released with the pancreatic juice into the small intestine, where it acts on proteins.
• The amino acids that are produced by the action of proteases are absorbed by the cells lining the digestive system and then absorbed into the blood stream.

Question 9

What type of protein is an enzyme?

Answer 9

A globular protein.

Question 10

What is activation energy?

Answer 10

• The energy required to initiate a reaction.

- Enzymes reduce the amount of activation energy thats needed, speeding up the rate of reaction.

Question 11

What is the active site?

Answer 11

Area of an enzyme with a shape complementary to a specific substrate, allowing the enzyme to bind a substrate with specificity.

Question 12

What is the enzyme-substrate complex?

Answer 12

A complex formed when a substrate is bound to the active site of an enzyme.

Question 13

What is the induced-fit hypothesis?

Answer 13

Modified lock and key explanation for enzyme action; the active site of the enzyme is modified in shape by binding to the substrate.

Question 14

What factors affect enzyme activity?

Answer 14

• Temperature
• pH
• Enzyme concentration
• Substrate concentration

Question 15

How does enzyme concentration affect the rate of reaction?

Answer 15

1) The more enzyme molecules there are in a solution, the more likely a substrate molecule is to collide with one and form an enzyme-substrate complex.
2) So increasing the concentration of the enzyme, increases the rate of reaction.
3) However, when the amount of substrate is limited, adding more enzyme has no further effect.

Question 16

How does substrate concentration affect the rate of reaction?

Answer 16

1) The higher the substrate concentration, the faster the reaction as it is more likely that there will be a collision between substrate and an enzyme.
2) However when all the active sites are full, an increase in substrate concentration has no further effect.

Question 17

How does temperature affect the rate of reaction?

Answer 17

1) As temperature increases, the particles move faster and collide more frequently.
2) In an enzyme-controlled reaction an increase in temperature will result in more frequent successful collisions between substrate and enzyme.
3) This leads to an increase in the rate of reaction.

Question 18

What is the temperature coefficient (Q10)?

Answer 18

The temperature coefficient or Q10 value for a reaction shows how much the rate of a reaction changes when the temperature is raised by 10 degrees.

Question 19

What is the equation to calculate Q10?

Answer 19

(Rate at higher temp)/(Rate at lower temp)

Question 20

How can enzymes denature?

Answer 20

1) At higher temperatures the bonds holding together the protein together vibrate more.
2) As the temperature increases, the vibrations increase until the bonds strain and then break.
3) The breaking of these bonds results in a change in the precise tertiary structure of the protein.
4) The active site changes shape and is no longer complementary to the substrate. The enzyme has denatured

Question 21

How can you measure the rate of an enzyme-controlled reaction?

Answer 21

1) You can measure how rate of reaction by using the enzyme catalase to catalyse the breakdown of hydrogen peroxide into water and oxygen. Then measure the volume of oxygen produced and how fast its given off.
2) You can also measure the disappearance of the substrate. E.g the enzyme amylase catalyses the breakdown of starch into maltose. It’s easy to detect starch using a solution of iodine. Time how long it takes for the starch to disappear by regularly sampling the starch solution.

Question 22

What are cofactors?

Answer 22

Non protein components necessary for the effective functioning of an enzyme.

Question 23

Examples of some cofactors

Answer 23

• Inorganic molecules or ions.
• They work by helping the enzyme and substrate to bind together.
• They don’t directly participate in the reaction so aren’t used up or changed in any way.
• E.g chloride ions are cofactors for the enzyme amylase.

Question 24

What are coenzymes?

Answer 24

• Cofactors that are organic molecules.
• They participate in the reaction and are changed by it.
• They often act as carriers, moving chemical groups between different enzymes.
• They’re continually recycled during the process.
• Vitamins are often sources of coenzymes.

Question 25

What is a prosthetic group?

Answer 25

• If a cofactor is tightly bound to the enzyme, its known as a prosthetic group.
• E.g zinc ions are a prosthetic group and are a permanent part of the enzyme’s active site.

Question 26

What are competitive inhibitors?

Answer 26

An inhibitor that competes with substrate to bind to active site on an enzyme.
- They block the active site so the substrate molecule can’t fit in.

Question 27

What are non-competitive inhibitors?

Answer 27

• An inhibitor that binds to the enzyme away from its active site. The site they bond to is known as the enzyme’s allosteric site.
• This causes the enzyme to change shape so the substrate molecules can longer bind in.
• They don’t compete with the substrate molecules to bind to the active site because they are a different shape.

Question 28

When is inhibition irreversible?

Answer 28

If they’re strong, covalent bonds, the inhibitor can’t be removed easily and the inhibition is irreversible.

Question 29

When is inhibition reversible?

Answer 29

If they’re weaker hydrogen bonds or weak ionic bonds, the inhibitor can be removed and the inhibition is reversible.

Question 30

What is a metabolic pathway?

Answer 30

• A series of connected metabolic reactions.
• The product of the first reaction takes part in the second reaction.
• Each reaction is catalysed by a different enzyme.

Question 31

What is end-product inhibition?

Answer 31

When the final product in a metabolic pathway inhibits an enzyme that acts earlier on in the pathway.
It’s reversible.
It regulates the pathway and controlling the amount of end-product that gets made.