Enzymes Module 2

Question 2

Function of an enzyme?

Answer 2

To speed up metabolic reactions, by acting as a biological catalyst

Question 3

An example of an intracellular enzyme (works within cells)?

Answer 3

The enzyme catalase breaks down hydrogen peroxide to harmless oxygen and water Hydrogen peroxide is the toxic by product of some cellular reactions, and can kill cells

Question 4

2 Examples of extracellular enzymes (work outside cells)?

Answer 4

The enzyme Amylase is found in saliva and is secreted into the mouth by cells in the saliva gland, it catalyses the hydrolyses of starch into maltose The enzyme trypsin catalyses the hydrolysis of peptide bonds so breaks down large polypeptides. It’s produced in the pancreas, and secreted into the small intestine

Question 5

What type of protein are enzymes?

Answer 5

Globular

Question 6

What do enzymes have which makes them specific to certain molecules?

Answer 6

An active site with a specific shape, which is where the molecule binds to, so they have to be complementary

Question 7

What level of structure determines the active site?

Answer 7

Tertiary structure

Question 8

How do enzymes reduce activation energy and therefore speed up the rate of reaction?

Answer 8

When a substance binds to an enzyme, an enzyme substrate complex is formed, this then lowers the activation energy (amount of energy that needs to be supplied to the chemicals before the reaction will start) If 2 substrate molecules need to be joined, then attaching the enzyme holds them closer together, reducing any repulsion between the molecules so they can bind more easily If the enzyme is catalysing a break down reaction, fitting into the active site puts a strain on the bonds in the substrate, this strain means the substrate molecule breaks up more easily

Question 9

Describe the lock and key model?

Answer 9

The substrate binds to the active site of the enzyme as complementary , and forms an enzyme substrate complex An enzyme product complex is then formed and products are released, leaving the enzyme unchanged after the reaction

Question 10

What does the induced fit model add to the lock and key model?

Answer 10

That when the substrate binds to active site, the active site changes shape slightly to fit the substrate more closely

Question 11

Explain the process of heating an enzyme up to denaturation?

Answer 11

Initially rate of reaction will increase, as the increase in thermal energy means an increase in kinetic energy, meaning molecules move faster so more frequent collisions and also more successful collisions, so more enzyme substrate complexes formed per unit time. However if temperature reaches a certain point, starts to denature. The rise in temperature makes the molecules vibrate more, which then starts to break bonds in tertiary structure (weakest to strongest). Causes tertiary shape to change, and enzyme and substrate are no longer complementary

Question 12

What is the temperature coefficient (Q10)?

Answer 12

Shows how much the rate of reaction changes when there’s an incresase of 10 degrees Before the optimum enzymes have a value of around 2

Question 13

What can a different pH do to the optimum, do to an enzyme?

Answer 13

H+ ions and OH- ions can disrupt the hydrogen and ionic bonds, causing the tertiary structure to change and therefore the active, decreasing the rate of reaction

Question 14

What does increasing the enzyme concentration do?

Answer 14

Makes it more likely for a substrate and an enzyme to collide and for an enzyme-substrate complex, therefore increases the rate of reaction, but only up to a certain point as if there’s a limited amount of substrate

Question 15

What’s the saturation point?

Answer 15

When adding more substrate doesn’t make a difference, as all the active sites are taken up

Question 16

2 ways to measure the rate of an enzyme controlled reaction?

Answer 16

Measure how fast the product of the reaction appears, eg in the reaction of catalase on hydrogen peroxide, measure how much Oxygen is produced in an upside down cylinder in water Can measure the disappearance of substrate, eg the enzyme amylase catalyses the reaction of starch to maltose, so during the reaction can keep adding sample to pottasium iodide and iodine solution, untill it doesn’t go blue/black, then you know all starch has disappeared.

Question 17

What’s a cofactor?

Answer 17

Non protein substance, that attaches to an enzyme allowing it to work

Question 18

Example of a inorganic cofactor?

Answer 18

Chloride ion, helps amylase enzyme bind to starch Aren’t affected during the reaction

Question 19

What can an organic cofactor be known as?

Answer 19

Coenzymes, usually are sources from vitamins

Question 20

What do coenzymes do during a reaction?

Answer 20

They participate in the reaction, so are changed Often act as carries, moving chemical groups between different enzymes

Question 21

What’s a cofactor known as if it’s tightly bound to an enzyme, and an example?

Answer 21

Prosthetic group, eg Zn(2+) in cabonic anhydrase (which catalyses the production of carbonic acid, from water and CO2)

Question 22

Explain what a competitive inhibitor is and how it works?

Answer 22

They are molecules that have similar shape to that of substrate molecules They compete with the substrate molecules to bind to the active site, but no reaction takes place, so they block the place for the substrate to react

Question 23

Explain what a non competitive inhibitor is and how it works?

Answer 23

Molecules that bind to the enzyme at the alosteric site Causes the active site to change the shape so the substrate molecules can no longer bind to it

Question 24

What makes an inhibitor reversible or non reversible?

Answer 24

Reversible if they’re bonded via weaker bonds such as hydrogen bonds Irreversible if they are bonded via strong hydrogen bonds

Question 25

Examples of enzyme inhibitors?

Answer 25

Some drugs, and metabolic poisions

Question 26

How are metabolic pathways regulated by end-product inhibition?

Answer 26

Metabollic pathway is a series of connected metabolic reactions, so the product of the first reaction takes part in the second reaction, each reaction is catalysed by a different enzyme Many enzymes are inhibited by the product of the reaction they catalyse, this is known as product inhibition End product inhibition is when the final product of the metabolic pathway, inhibits an enzyme which acts earlier on in the pathway So when there’s too much of final product will inhibit an earlier enzyme more, preventing too much being made

Question 27

Why are some enzymes sometimes synthesised as inactive precursor enzymes?

Answer 27

So they don’t damage the cells they are synthesised in