Enzymes

Question 1

What is the lock and key model?

Answer 1

The substrate fits the into the enzyme the same way that a key fits a lock.

Question 2

What is the induced fit model?

Answer 2

As the substrate binds, the enzymes active site changes shape slightly to fit the substrate more closely.

Question 3

Which model is widely accepted?

Answer 3

Induced fit model

Question 4

What do enzymes do?

Answer 4

They increase the rate of reactions- biological catalysts

Question 5

What type of protein are enzymes?

Answer 5

Globular proteins

Question 6

What is the structure of enzymes?

Answer 6

Have hydrophilic amino acids on their surface and hydrophobic amino acids are buried within the centre of the protein- which makes them soluble in water.

Question 7

What is an enzyme-substrate complex?

Answer 7

When the enzyme and substrate are binded together.

Question 8

What are intracellular enzymes?

Answer 8

Enzymes that are produces and function inside the cell

Question 9

What are extracellular enzymes?

Answer 9

Enzymes that are secretes by cells and catalyse reactions outside of cells (e.g. digestive enzymes in the gut)

Question 10

How are all enzymes produced?

Answer 10

Produced via the process of protein synthesis inside cells

Question 11

What is an example of an intracellular enzymes?

Answer 11

Catalase

Question 12

What are two examples of extracellular enzymes?

Answer 12

Amylase and trypsin

Question 13

What is the function of catalase?

Answer 13

Hydrogen peroxide is produced as a by-product of many metabolic reactions.
- It is harmful to cells.
Catalase converts hydrogen peroxide into water and oxygen, preventing any damage to cells or tissues

Question 14

What is the function of amylase?

Answer 14

• Amylase is involve in carbohydrate digestion, it hydrolyses starch into simple sugars (maltose).
• It is secreted by the salivary glands an the pancreas, for digestion of starch in the mouth and small intestine.

Question 15

What is the function of trypsin?

Answer 15

Enzyme secreted by the pancreas and enters the small intestine, which breaks proteins down into peptides and amino acids.

Question 16

What is the activation energy?

Answer 16

The amount of energy needed by the substrate to become just unstable enough for a reaction to occur and for products to be formed.

Question 17

What do enzymes do to the activation energy?

Answer 17

Rather than lowering the overall activation energy change of the reaction, enzymes work by providing an alternative energy pathway with a lower activation energy.

Question 18

What do buffer solutions do?

Answer 18

• Buffer solutions each have a specific pH
• Buffer solutions maintain this specific pH, even if the reaction taking place would otherwise cause the pH of the reaction mix to change.

Question 19

Why do enzymes denature in extremes of pH?

Answer 19

Hydrogen and ionic bonds hold the tertiary structure of the enzyme together
- Below and above the optimum pH of the enzyme can cause these bonds to break
- This alternatives the shape of the active site, which means enzyme-substrate complexes form less easily

Question 20

How does an increased temperature affect enzymes?

Answer 20

This means there is more kinetic energy and so the molecules move faster. This makes the enzymes more likely to collide with the substrate molecules. The energy of the collisions also increases, which means each collision is more likely to result in a reaction.

Question 21

What is the effect on enzymes if the temperature gets too high?

Answer 21

If the temperature goes above a certain level, the kinetic energy causes some bonds to break that hold the enzyme in shape. This means the active site changes shape and the enzyme and substrate no longer fit together.
At this point the enzyme is denatured- it no longer functions as a catalyst

Question 22

What does the temperature coefficient or Q10 show?

Answer 22

Shows how much the rate of reaction changes when the temperature is raised by 10°C.

Question 23

What is the equation for calculating the temperature coefficient?

Answer 23

Q10= Rate at higher temperature/ rate at lower temperature

Question 24

What is the optimum pH for most human enzymes?

Answer 24

pH7 (neutral)

Question 25

What is the optimum temperature for most human enzymes?

Answer 25

Around 37°C

Question 26

How does increasing the enzyme concentration affect the rate of reaction?

Answer 26

The more enzymes molecules there are in a solution, the more likely a substrate molecule is to collide with one and form an enzyme-substrate complex. So increasing the conc of enzymes increases the rate of reaction.

Question 27

How does increasing the enzyme concentration affect the rate of reaction, if there is a limited amount of substrate?

Answer 27

If the amount of substrate is limited, there comes a pint when there’s more than enough enzyme molecules to collide with all of the available substrates, so adding more enzyme has no further effect.

Question 28

How does increasing the substrate concentration affect the rate of reaction?

Answer 28

The higher the substrate concentration, the faster the reaction- more substrate molecules means a collision between substrate and enzyme is more likely and so more active sites will be used.

Question 29

Why does increasing the substrate concentration only affect the rate of reaction up to a point?

Answer 29

Increases the rate of the reaction up until there is a ‘saturation’ point. After that, there are so many substrate molecules that all enzymes active sites are full, and adding more substrate makes no difference to the rate of reaction.

Question 30

What happens when the substrate concentration decrease with time during a reaction?

Answer 30

Unless more substrate is added to the reaction mix, so if no over varibales are changed, the rate of reaction will decrease over time too. This makes the inital rate of reaction the highest rate of reaction.

Question 31

What is one way of measuring the rate of an enzyme-controlled reaction? (products)

Answer 31

Can measure how fast the products of the reaction appears. For example can measure the enzyme catalase. Can do this by measuring the rate of oxygen produced, because catalase catalyses the breakdown of hydrogen peroxide into water and oxygen.

Question 32

What is another way of measuring the rate of enzyme- controlled reactions? (disappearance of substrate).

Answer 32

Can also measure the disappearance of the substrate and use this to comapre the rate of reaction under different conditions. For example the enzyme amylase catalyses the breakdown of starch to maltose. Its easy to detect starch using a solution of potassium iodide and iodine. You can time how long it takes for the starch to disappear by regularly sampling the starch solution. You can then alter the conditions of the reaction and compare rates .

Question 33

What is a cofactor?

Answer 33

A substance that some enzymes need to work

Question 34

What do cofactors do?

Answer 34

Some cofactors are inorganic molecules or ions. They work by helping the enzyme and substrate bind together They don’t participate in the reaction so aren’t used up or chnage in anyway. For example, chloride ions are cofactors of the enzyme amylase.

Question 35

What are coenzymes?

Answer 35

Larger organic (carbon-containing) molecules.

Question 36

What do coenzymes do?

Answer 36

They partipate in the reaction and are changed by it. They often act as carriers, moving chemical groups between different enzymes. They’re continually recycled during this process. Vitamins are often sources of coenzymes.

Question 37

What is a prosthetic group?

Answer 37

When a coenzyme is permanently part of the enzyme’s active site

Question 38

What is an example of a prosthetic group?

Answer 38

Zinc ions are an example of a prosthetic group for carbonic anhydrase (an enzyme in red blood cells, which catalyses the production of carbonic acid from water and carbon dioxide). The zinc ions are permanently part of the enzyme’s active site.

Question 38

What is an example of a prosthetic group?

Answer 38

Zinc ions are an example of a prosthetic group for carbonic anhydrase (an enzyme in red blood cells, which catalyses the production of carbonic acid from water and carbon dioxide). The zinc ions are permanently part of the enzyme’s active site.

Question 39

What are enzyme inhibitors?

Answer 39

Molecules that bind to the enzyme that they inhibit

Question 40

How do competitive inhibitors work?

Answer 40

They have a similar shape to that of the substrate molecule.
They compete with the substrate molecules to bind to the active site, but no reaction takes place (when inhibitor binds to enzyme).
Instead they block the active site, so no substrate molecules can fit.

Question 41

What determines how much an enzyme is inhibited?

Answer 41

Depends on the relative concentrations of the inhibitor and the substrate.
High conc of inhibitor- take up nearly all of the active sites and hardly any of the substrate will get to the enzyme
Higher conc of substrate- the substrates chances of getting to an active site before an inhibitor increases. So increasing the conc of substrate will increase the rate of reaction (up to a point).

Question 42

What do non-competitive inhibitors do?

Answer 42

Bind to the enzyme away form its active site. The site they bind to is known as the enzyme’s allosteric site.

Question 43

What happens when a non-competitive inhibitor binds to an enzyme?

Answer 43

They cause the active site to change shape so the substrate molecule can no longer bind to it.
They don’t compete with the substrate molecules to bind to the active site because they are a different shape.

Question 44

What happens if you increase the substrate concentration in the presence of competitive inhibitors?

Answer 44

Won’t make an y difference to the rate of reaction- enzyme activity will still be inhibited.

Question 45

Which inhibitors are irreversible?

Answer 45

Those with strong, covalent bonds, because the inhibitor cannot be easily removed ans the inhibition is therefore irreversible.

Question 46

Which inhibitors are reversible?

Answer 46

Those with weaker hydrogen bonds, or weak ionic bonds, because the inhibitor can be removed and therefore the inhibition is reversible.

Question 47

What is a metabolic pathway?

Answer 47

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

Question 48

What is product inhibition?

Answer 48

When enzymes are inhibited by the product of the reaction they catalyse.

Question 49

What is end-product inhibition?

Answer 49

When the final product in a metabolic pathway inhibits an enzyme that acts earlier on in the pathway.

Question 50

Why is end-product inhibition useful?

Answer 50

It is a nifty way of regulating the pathway and controlling the amount of end-product that gets made. For example:
- Phosphofructokinase is enzyme involved in the metabolic pathway that breaks down glucose to make ATP.
- ATP inhibits the action of phosphofructokinase- so a high level of ATP prevents more ATP being made

Question 51

Why is it useful that both product and end-product inhibition are reversible?

Answer 51

So when the level of product starts to drop, the level of inhibition will start to fall so the enzyme can start to function again- meaning more product can be made.

Question 52

Why are enzymes sometimes synthesised as inactive precursors in metabolic pathways?

Answer 52

To prevent them causing damage to cells. For example, proteases (which break down proteins) are synthesised as inactive precursors to stop them damaging proteins in cells in which they’re made in.
Part of the precursor molecule inhibits its action as an enzyme. One this part is removed (e.g. via a chemical reaction) the enzyme becomes active.

Question 53

Which poisons are enzyme inhibitors?

Answer 53

Arsenic inhibits the action of pyruvate dehydrogenase, an enzyme that catalyses repiration reactions. Cells that can’t respire die