Enzymes

Question 1

How do you assess the rate of enzymic reactions?

Answer 1

Measure time course for:
-formation of the products of the reaction
-the disappearance of the substance

Question 2

What happens to the rate when the graph of ‘effect of substrate concentration on rate of reaction’ plateaus?

Answer 2

Constant rate

Question 3

Why are enzymes less efficient at low temps?

Answer 3

-rate of reaction is slowed down
-due to reduced kinetic energy of the reactant molecules

Question 4

Describe the effect of temperature on the rate of an enzyme-controlled reaction.

Answer 4

-increase in temp provides molecules with more kinetic energy, resulting in more frequent successful frequent collisions between active sites and substrate molecules
-more enzyme-substrate complexes formed
-this increases rate of reaction up to the optimum temp where rate of reaction is at its maximum
-continuing to increase the temperature causes the tertiary structure of the enzyme to denature as hydrogen and ionic bonds are broken
-rate of reaction decreases as the substrate can’t bind to the altered active site (less e-s complexes formed)

Question 5

What happens to proteins above 50 degrees?

Answer 5

• denaturation is permanent
• the tertiary structure is irreversibly altered
  -substrate can’t bind to the active site

Question 6

What’s an enzymes optimum pH?

Answer 6

-the rate of reaction is at its maximum
-most enzymes are active over a narrow pH range

Question 7

How does pH cause denaturation?

Answer 7

-very different pH’s from from the optimum can cause denaturation
-the change in pH alters ionic charges of acidic and basic groups
-hydrogen and ionic bonds are broken altering the tertiary structure and active site
-the substrate can’t bind to the altered active site

Question 8

What are enzyme inhibitors?

Answer 8

-a number of chemicals can act as enzyme inhibitors
-slowing down the rate of enzyme catalysed reactions

Question 9

Explain how competitive inhibitors effect rate of reaction.

Answer 9

-the inhibitor has a similar structure to the substrate molecule
-competes with it for the attachment to the active site
-binds to active site and blocks the substrate from doing so
-rate of reaction is reduced as there are fewer enzyme-substrate complexes

Question 10

How can competitive inhibition be reduced?

Answer 10

Addition of more substrate

Question 11

Explain an example of a competitive inhibitor and how it’s treated.

Answer 11

-carbon monoxide
-competes with oxygen in haemoglobin
-treated by giving 100% oxygen to the patient to flush out the carbon monoxide

Question 12

Sketch a graph showing the effect of a competitive inhibitor on rate of reaction compared with no inhibitor present

Answer 12

X= substrate conc
Y=rate of reaction

Question 13

Explain how non-competitive inhibitors effect rate of reaction.

Answer 13

-the inhibitor is not similar in structure to the substrate
-it binds at another place other than the active site to form an enzyme-inhibitor complex
-alters tertiary structure and shape of the active site
-the substrate can’t attach or substrate binds but no product is formed
-the degree of inhibition is completely dependant on the mount of inhibitor present

Question 14

Can you reduce the inhibition of non-competitive inhibitors?

Answer 14

-no
-the addition of more substrate wont reduce this inhibition

Question 15

Draw a graph to show the effect of non-competitive inhibitors on rate of reaction compared with no inhibitor present.

Answer 15

X=substrate conc
Y=rate of reaction