enzymes

Question 1

what are enzymes?

Answer 1

biological catalysts

Question 2

what are enzymes made from?

Answer 2

globular proteins

Question 3

give an example of an intracellular enzyme

Answer 3

catalayse - which is inside liver cells, breaking down hydrogen peroxide into oxygen and water

Question 4

give an example of an extracellular enzyme

Answer 4

trypsin - inside the small intestine and hydrolyses proteins

Question 5

what protein structure are enzymes?

Answer 5

tertiary structure

Question 6

what is activation energy?

Answer 6

the minimum amount of energy for a reaction to occur

Question 7

what do enzymes do to the activation energy?

Answer 7

they lower it by attaching to the substrate. this speeds up the reaction

Question 8

What are the two types of enzyme action?

Answer 8

• intercellular and extracellular

Question 9

What is the structure of an enzyme?

Answer 9

They are made from an active site which has a specific shape, this binds to a substrate molecule

Question 10

How does an enzyme work?

Answer 10

The substrate fits into the active site, their shapes are complimentary. Of the substrate shape does not fit the active site then the reaction won’t be catalysed.

Question 11

Describe the lock and key model

Answer 11

The substrate fits into the enzyme like a key fits into a lock. They are an exact match.

Question 12

What’s wrong with the lock and key model?

Answer 12

New evidence showed that the enzyme substrate changed shape slightly to complete the fit, loving the substrate in even more to the enzyme?

Question 13

Describe the induced fit theory

Answer 13

The substrate doesn’t only have to be the right shape to fit the active site, it has to make the active site change shape in the right way as well. This locks in the enzyme substrate complex.

Question 14

What factors affect enzyme activity?

Answer 14

• temperature
• pH
• enzyme concentration
• substrate concentration

Question 15

How does temperate affect enzyme activity?

Answer 15

The rate of reaction increases when the temperature increases as more heat energy means more kinetic energy, so the molecules move faster, thus creating more collisions.
If the temperature becomes too high then the reaction stops as the vibrations break the bonds that hold the enzymes in shape, causing the active site to change shape and the substrate to not fit. This is referred to as denaturing

Question 16

What is the temperature coefficient?

Answer 16

A value that shows how much the rate of reaction changes when the temperature is raised by 10°.
At temperatures before the optimum a Q10 value of 2 means the rate doubles when the temperature increases by 10°. Most enzyme controlled reactions have a rate of around two.

Question 17

What is the temperature coefficient formula?

Answer 17

Q10 = rate at higher temperature/rate at lower temperature

Question 18

How does pH affect enzyme activity?

Answer 18

All enzymes have an optimum pH which is usually around pH 7. However pepsin works best at an acid pH 2 which is useful as it’s found in the stomach.
When an enzyme is above or below the optimum pH the H+ and OH- ions can mess up the ionic bonds and hydrogen bonds that hold the enzymes tertiary structure in place. This makes the active site change shape and the enzyme to denature.

Question 19

How does enzyme concentration affect the rate of reaction?

Answer 19

The more enzyme molecules in a solution the more likely a substrate molecule is to collide with one to form an enzyme substrate complex. So increasing the concentration increases the rate of reaction
However, if the amount of substrate is limited then there is more than enough enzymes available so adding more substrate has no effect.

Question 20

How does substrate concentration affect rate of reaction?

Answer 20

The higher the substrate concentration the faster the rate of reaction as more substrate molecules cause more frequent collisions.
However after a certain point the enzyme becomes saturated and all the active sites become full. After that point, adding more substrate doesn’t make a difference.
Substrate concentration decreases with time, so if no other variables are changed the rate of reaction will decrease over time

Question 21

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

Answer 21

• measure how fast the product of the reaction appears
• measure the disappearance of the substrate by timing how long it takes for the starch to disappear by regularly sampling the solution and compare the rate under different conditions

Question 22

How can you investigate the effect of temperature on catalase activity?

Answer 22

1. Set up boiling tubes with the same volume and concentration of hydrogen peroxide. To keep the pH constant, add equal volume of a buffer solution
2. Set up the apparatus to measure the volume of oxygen produced from each boiling tube, for example upside down measuring cylinders.
3. Put each boiling tube tub a water bath set to a different temperature along with another tube containing catalase
4. Use a pipette to add the same volume and concentration of catalase to each solution
5. Record how much oxygen is produced in the first 60s using a stopwatch
6. Repeat the experiment to find the mean

Question 23

What are cofactors?

Answer 23

Non protein substances that bind to enzymes . Some will only work us that is another protein substance bound to them

Question 24

What are inorganic cofactors?

Answer 24

Cofactors that work by helping the enzyme and substrate bind together. They don’t directly participate in the reaction and so aren’t used or changed in any way

Question 25

What are organic cofactors, and what’s another name for them?

Answer 25

Sometimes referred to as coenzymes, they participate in the reaction and are changed by it. They act as carriers, moving chemical groups been different enzymes and are continually recycled

Question 26

What happens if a cofactor is tightly bound to the enzyme?

Answer 26

It’s known as a prosthetic group, and becomes a permanent part of the active site.

Question 27

What’s an example of a prosthetic group cofactor?

Answer 27

Zinc ions are a prosthetic group for carbonic anhydrase which catalyses the production of carbonic acid from water and carbon dioxide. The zinc ions are a permanent part of the active site

Question 28

What can enzyme activity be prevented by?

Answer 28

Enzyme inhibitors, either competitive or non competitive

Question 29

What are competitive inhibitors?

Answer 29

Molecules that have a similar shape to that of the substrate molecules, they compete with the substrate molecules to bind to the active site but no reaction takes place, instead they block the active site so no substrate can fit into it.

Question 30

What does enzyme inhibition depend on?

Answer 30

• the relative concentration of the inhibitor
• the relative concentration of the substrate
If there’s a high concentration of the inhibitor it will take away all of the active site’s and hardly any of the substrate will get to the enzyme, however if you increase the concentration of the substrate, the substrates chances are higher so rate of reaction increases

Question 31

What are non competitive inhibitors?

Answer 31

Molecules that bind to the enzyme away from its active site (allosteric site) this causes the active site to change shape so no substrate can bind to it. They don’t compete with the substrate as they are a different shape and don’t bind to the active site. Increasing the concentration will not make any difference to reaction rate.

Question 32

What does inhibitor being reversible or irreversible depend on?

Answer 32

The strength of bonds between the enzyme and the inhibitor

Question 33

What happens when an inhibitor has strong covalent bonds?

Answer 33

The inhibitor can’t be removed easily and becomes irreversible

Question 34

What happens if an inhibitor has weak ionic bonds or hydrogen bonds?

Answer 34

The inhibitor can be removed and the inhibition is reversible

Question 35

What is end product inhibition?

Answer 35

When enzymes are inhibited by the product that they catalyse. It’s when the final product in a metabolic pathway inhibits an enzyme that acts earlier on in the pathway

Question 36

What does end product inhibition control?

Answer 36

The amount of end product that gets made, for example they are reversible so when product starts to drop the level of inhibition will start to fall and the enzyme can start to function again, making more product

Question 37

Why are some enzymes synthesised as inactive precursors?

Answer 37

They prevent them causing damage to cells as part of the precursor inhibits its action as an enzyme and is this part is removed the enzyme becomes active