2.4 Enzymes

Question 1

What are enzymes ?

Answer 1

They are proteins that acts as biological catalysts, to speed up the rate of reaction. Found in living organisms and affects structures in an organism.

Question 2

What is intracellular enzyme action ?

Answer 2

Enzymes work inside the cell. Eg. Catalase is an enzyme that works inside cells to catalyse breakdown of hydrogen peroxide to oxygen and water. It is toxic by-product of several cellular reactions.

Question 3

What is extracellular enzyme action ?

Answer 3

Enzymes that work outside the cell. Eg. Amylase works outside the cell in human digestive system. Found in saliva and catalyses breakdown of starch into maltose.

Question 4

What type of proteins are enzymes ?

Answer 4

They are globular proteins with an active site which is complementary to the substrate allowing them to bind together.

Question 5

What determines an enzymes specific shape ?

Answer 5

The tertiary structure of a protein determines the specific shape.

Question 6

What do enzymes lower in reactions ?

Answer 6

They lower the activation energy needed for successful reactions at lower temperatures. This speeds up the rate of reaction.

Question 7

Substrate complex

Answer 7

Formed when enzyme binds to substrate

Question 8

What is the lock and key hypothesis ?

Answer 8

Enzymes have a complimentary shape. When enzyme substrate complex is formed, it changes shape slightly, this locks the substrate more tightly to enzyme.

Question 9

What is the induced fit model ?

Answer 9

Substrate has to make active site change shape in the right way as well as the enzyme.

Question 10

What happens to rate of reaction when temperature increases ?

Answer 10

Rate of reaction increases. This is because there is more heat, so more KE so molecules move faster. This increases energy of collisions, so more likely to result in collisions.

Question 11

What will happen to enzymes if temperature is too high ?

Answer 11

If temperature is too high, the reaction will stop as it causes enzyme to denature (enzyme molecules vibrate causing bonds to break).

Question 12

What is the temperature coefficient ?

Answer 12

Shows how much rate or reaction changes when temperature is raised by 10’C.

Question 13

What is the optimum pH ?

Answer 13

Optimum pH is the pH that controlled enzyme reaction works fastest.

Question 14

What happens when pH goes above and below optimum pH ?

Answer 14

H+ and OH- ions break ionic and hydrogen bonds that hold enzymes tertiary structure in place. Changes active site so enzyme would be denatures.

Question 15

What happens to rate of reaction if there is a higher enzyme concentration ?

Answer 15

The more enzyme molecules there are in a solution, the more likely a substrate molecule will collide to form enzyme substrate complex. Increases rate of reaction.

Question 16

What effect will adding more enzymes do if substrate is limited ?

Answer 16

If substrate is limited, then adding more enzymes will have no further effect.

Question 17

What happens to rate of reaction when substrate concentration increases ?

Answer 17

Higher the substrate concentration, the faster the reaction. More substrate means more collisions between enzymes. Only true until saturation point (all active sites are full). Enzyme concentration is limiting factor.

Question 18

What are cofactors ?

Answer 18

Some enzymes only work is there is another non-protein substance bound to them. Cofactors are the non-protein substance. They can be inorganic or organic.

Question 19

What are inorganic cofactors ?

Answer 19

They help enzyme and substrate bind together. They do not directly participate in reaction, so are not used up or changed. Eg., chloride ions

Question 20

What are organic cofactors (coenzyme)?

Answer 20

They help enzyme and substrate bind together. They participate in the reaction and are changed by it. They act as carriers, moving chemical groups between enzymes. Eg., vitamins

Question 21

What is a prosthetic group ?

Answer 21

If a cofactor is tightly bound to enzyme, this is known as the prosthetic group.

Question 22

What are enzyme inhibitors ?

Answer 22

Enzymes can be prevented by enzyme inhibitors, which are molecules that bind to the enzyme they inhibit.

Question 23

What are competitive inhibitors ?

Answer 23

They have a similar shape to substrate molecule and compete with substrate molecule to bind to active site but no reaction takes place. (They block the active site).

Question 24

What does increasing the concentration of a competitive inhibitor do to the reaction ?

Answer 24

A high concentration of inhibitor takes up most of the active site and hardly any substrate will get to the enzyme. This increases the rate of reaction up to a point.

Question 25

What are non-competitive inhibitors ?

Answer 25

They bind to the enzyme away from the active site (allosteric site). Causes enzyme to change shape so substrate molecules can no longer bind to it.

Question 26

What does increasing concentration on non-competitive inhibitor do to the reaction ?

Answer 26

They do not compete with the substrate, so increase concentration of the substrate will not make any difference to rate of reaction.

Question 27

What are reversible inhibitors ?

Answer 27

Inhibitors can be reversible, where they do not bind permanently to enzyme. They have weak hydrogen or ionic bonds, between the enzyme and the substrate, that do not require lots of energy to break.

Question 28

What are irreversible inhibitors ?

Answer 28

Inhibitors can be irreversible, where they bind permanently to the enzyme. They have strong covalent bonds , between the enzyme and substrate, that are hard to break.

Question 29

How do antiviral drugs work in terms of inhibitors ?

Answer 29

Prevents virus replicating and inhibit enzymes reverse transcriptase.

Question 30

How to antibacterial drugs work in terms of inhibitors ?

Answer 30

Weakens cell wall, causing cell to burst, which kills the bacterium. Inhibits enzyme transpeptidase.

Question 31

What are metabolic poisons ?

Answer 31

They interfere with metabolic reactions causing damages, illness and death.

Question 32

What are end-product inhibitions ?

Answer 32

The term used for enzyme inhibition that occurs when the product of a reaction acts as an inhibitors to the enzyme that produces it. Example of a negative feedback mechanism.

Question 33

Are product and end product inhibitor reversible ?

Answer 33

Yes

Question 34

What happens when levels of product drops with product inhibition ?

Answer 34

When a level of product drops, inhibition falls and enzyme can start to function again, so more product is made.

Question 35

What is precursor activation ?

Answer 35

Many enzymes are produced in inactive forms, known as inactive precursor enzymes, particularly enzymes that can cause damage within cells producing them or where they are released.

Question 36

What is product inhibition ?

Answer 36

Products of 1st reaction of metabolic pathway takes places in the 2nd etc. Each reaction is catalysed by a different enzyme known as product inhibition.

Question 37

What happens when final product inhibits enzymes ?

Answer 37

When final product of metabolic pathway inhibits enzymes that act earlier in the reaction, end product inhibition regulates pathway and controls the amount of product made.

Question 38

What is a metabolic pathway ?

Answer 38

Metabolic pathway is a series of connected metabolic reactions. 1st reaction takes place in the 2nd and so on. They are regulated by product inhibitors .