Enzyme

Question 1

What is enzyme?

Answer 1

Biological catalysts
speeds up chemical reaction

Question 2

What is an example of intracellular enzyme?

Answer 2

Catalase catalyses the breakdown of hydrogen peroxide (H2O2) to harmless oxygen and water
It works inside the cell

Question 3

What is an example of extracellular enzyme?

Answer 3

Amylase catalyses the hydrolysis of starch into maltose
It works outside the cell

Question 4

What is the structure of enzyme?

Answer 4

Globular protein
Have an active site, which is determined by the enzyme’s tertiary structure

Question 5

What is formed when the substrate binds to an enzyme’s active site?

Answer 5

Enzyme-substrate complex

Question 6

How does enzyme speed up reaction?

Answer 6

Enzymes reduce the amount of activation energy that’s needed.

Question 7

What is the ‘lock and key’ model?

Answer 7

The active site and the substrate have a complementary shape

Question 8

What is the ‘induced fit’ model?

Answer 8

As the substrate binds the active site changes shape slightly

Question 9

What are the factors affecting enzyme activity?

Answer 9

• Temperature
• pH value
• Enzyme concentration
• Substrate concentration

Question 10

How does temperature affect enzyme activity?

Answer 10

• More heat means increased in kinetic energy
• Increased chances of successful collision
• The rate of reaction increase until the enzyme reaches its optimum temperature
• If the temperature is too high, the enzyme molecules vibrate more.
• This breaks some of the bonds that hold the enzyme in shape
• The active site changes shape and the enzyme and the substrate no longer fit together
• The enzyme is denatured

Question 11

How to calculate temperature coefficient (Q10)

Answer 11

Rate at higher temperature/ Rate at lower temperature

Question 12

What is temperature coefficient (Q10)?

Answer 12

How much the rate of reaction changes when the temperature is raised by 10°C

Question 13

How does pH affect enzyme activity?

Answer 13

All enzymes have an optimum pH
Above or below the optimum pH, the H+ and OH- ions found in acids and alkalis can break the ionic bonds and hydrogen bonds that hold the enzyme’s tertiary struture
the enzyme denatured

Question 14

How does enzyme concentration affect enzyme activity?

Answer 14

• Steady increase as more active sites are available
• The more enzyme molecules there are in a solution, the more likely a molecule is to collide with one and form an enzyme-substrate complex
• If the subtrate amount is limited, the rate of reaction no longer increases and the curve flattens out

Question 15

How does substrate concentration affect enzyme acitivity?

Answer 15

• Steady increase as more substrate are available
• More substrate increases the chance of successful collision until a stauration point (Vmax)
• All active sites used - Increase in substrate concentration has no further effect
• The enzyme concentration becomes the limiting factor

Question 16

How to estimate the initial rate of reaction?

Answer 16

• Draw a tangent at t=0
• Calculate the gradient of the tangent

Question 17

What is cofactor?

Answer 17

• molecules or ions that help the enzyme and substrate to bind together
• They aren’t used up or changed in any way

Question 18

What is coenzyme?

Answer 18

• Organic cofactors
• often act as carriers, moving chemical groups between different enzymes
• They are continueally recycled during this process

Question 19

What is one example of coenzyme?

Answer 19

• Vitamins are often sources of coenzymes
• E.g. the coenzyme NAD is derived from vitamin B3

Question 20

What is one example of cofactor?

Answer 20

Cl- are inorganic cofactors for the enzyme amylase

Question 21

What is competitive inhibitors and how do they work?

Answer 21

• Molecules have a similar shape to that of substrate molecules.
• They block the active site, so no substrate can fit in
• rate increases as the substrate concentration is increased

Question 22

What is non-competitive inhibitors and how do they work?

Answer 22

• Molecule binds to the allosteric site, causing the active site to change shape so the substrate can no longer bind to it
• Increasing the substrate concentration has little effect on the rate

Question 23

What is reversible inhibition?

Answer 23

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

Question 24

What is irreversible inhibition?

Answer 24

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