Biol 1057 - Introduction to enzyme

Question 1

Outline metabolism

Answer 1

• Metabolism refers to all the reactions of the body
• Metabolic reactions need to happen quickly so that organisms
  can respond appropriately to changes in their environment

Question 2

Describe what is meant by an enzyme.

Answer 2

• Biological catalysts which lower activation energy of reactions they catalyse without being used which speeds up the reaction
• Enzymes are tertiary structure proteins and can also be RNA
• If the right molecules collide with
  sufficient energy, then a chemical
  reaction will occur

Question 3

Define catalyst

Answer 3

• A catalyst is a chemical that speeds up the rate of reaction and remains
  unchanged and reusable at the end of the reaction
• Biological catalysts for metabolic reactions are called enzymes (proteins)

Question 4

Describe why enzymes are specific.

Answer 4

• Active site specific and unique in shape as enzyme has specific primary structure
• and to specific folding & bonding in tertiary structure of protein
• Due to this specific active site, enzymes can only attach to substrates complementary in shape to form ES complex

Question 5

Outline how active sites work

Answer 5

• Active sites contain reactive molecules that can carry out all the steps
  of a reaction in a controlled way with lower activation energy
• When a substrate (or substrates) binds to the active site it is held in a
  specific orientation that facilitates its reaction

Question 6

Explain the induced fit model of enzyme action.

Answer 6

• Substrate binds to active site to form an enzyme substrate complex
• Induced fit causes active site changes shape slightly so its complementary to substrate
• • Reducing activation energy as strain placed on the bonds

Question 7

List the 4 factors which effect enzyme controlled reactions

Answer 7

• pH
• Temperature
• Substrate and Enzyme concentration
• Inhibitors are molecules that reduce or stop a reaction

Question 8

Describe the effect of pH on rate of reaction.

Answer 8

• Bonds to break in tertiary structure and active site shape to change leading to denaturation
• Stomach enzymes work best at pH=2
  Enzymes in the intestine work best at pH=8

Question 9

Describe the effect of temperature on rate of reaction.
HUMAN TEMP OPTIMUM

Answer 9

• Rate increases as temperature inceases as more kinetic energy so more successful collisions until optimum temperature- If temperature too high active site changes shape and ES complexes cannot form leading to denaturation as it MELTS LIPIDS AND DENTATURES PROTEINS

Question 10

Describe the effect of substrate and enzyme concentration on rate of reaction.
N/A

Answer 10

• Rate levels off when maximum ES complexes formed
• Low amount of substrate leads to less collisions between enzyme & substrate
• Low amount of enzyme leads to active sites being saturated and unable to work faster

Question 11

Describe the effect of inhibitors on rate of reaction.

Answer 11

COMPETITIVE INHIBITORS
- Increasing substrate concentration decreases their effect
- Inhibitor same shape to substrate
- Binds to active site preventing enzyme substrate complexes from forming
- NON-COMPETITIVE INHIBITORS
- Increasing substrate concentration has no effect
- Inhibitor binds to allosteric site causing conformational change to active site shape
- Therefore active site no longer complementary to substrateno ES complexes can form

Question 12

Briefly outline how lock and key model works

Answer 12

• Initially lock & key mode= rigid shape of active site complementary to only 1 substrate

Question 13

Define activation energy and cofactors

Answer 13

Activation energy is the energy
required to start a reaction
- A lot of enzymes rquire cofactors to get acticated

Question 14

Briefly outline inhibitors

Answer 14

• Inhibitors are molecules that reduce or stop a reaction
• Results in intertmediate compound not being produced so no end product can be produced
• End product acts as a non-competitive inhibitor binding to allosteric site on enzyme which controls production of an intermediate compound earlier in the pathway

This is an example of a negative feedback loop
which ensures the concentration of a product stays
roughly constant

Question 15

Describe end product inhibitoon

Answer 15

• If concentration of end product too high, more inhibion will occur and greater inhibition will leas to decrease in amount of end product produced
• If concentration of end product is decreased this will decrease inhibiton