1.4 - Enzymes

Question 1

What are Enzymes?

Answer 1

• Enzymes are protein molecules that act as biological catalysts.
• They have a specific region on their surface called an active site.
• Are not consumed in the reaction, but can be used over and over again
• Work inside cells (intracellular) or outside cells (extracellular)
• Most enzymes work inside cells as this is the site of cell metabolism

Question 2

What is an Active Site?

Answer 2

• Active site has a shape that is complementary to the shape of the reactants (substrates) that the enzyme catalyses
• Specific in their action
  - i.e.: one enzyme binds with one substrate

Question 3

What are regulatory Proteins?

Answer 3

• Protein molecules that regulate switching on/off genes
  
  • For example, repressor proteins that bind to particular sections of DNA to precent the transcription of that gene and therefore the production of its product
    
    • The Protein’s shape determines where it will bind

Question 4

What are Proteomics?

Answer 4

• Proteomics is the study of proteins.

- a Proteome is all of the proteins found in a cell organism at a given time.

Question 5

What is the role of an enzyme?

Answer 5

• All reactions involve bond breaking and bonds reforming.

- Enzymes aid in this process by lowering the amount of energy needed for the reaction.

Question 6

How do enzymes lower activation energy?

Answer 6

• The substrate binds to the active site of the enzyme by weak bonds, forming the enzyme-substrate complex.
• The active site changes shape slightly to form an even more exact fit.
• The bonds of the substrate are subjected to pressure, reducing activation energy and making the reaction more likely to occur.
• Product forms and breaks away from the enzyme, leaving the enzyme unchanged.

Question 7

Explain the specificity of an enzyme:

Answer 7

• The specificity of an enzyme is caused by the complementary fit between enzyme and substrate.
• The induced fit is primarily the change in the enzyme caused by the substrate binds to the active site of the enzyme.

Question 8

What conditions create an effect of Enzyme Activity?

Answer 8

• Each enzyme has a specific set of conditions under which it works best.
• Enzymes are sensitive to:
  - Changes in TEMP. pH and the presence of INHIBITORS.

Question 9

How does temperature have an effect on enzyme activity?

Answer 9

• Most human enzymes operate most effectively at 35-40*C
  
  • A higher temperature is generally a good way to speed up chemical reactions
    
    • As temperature increases the substrate molecules will collide more frequently, thus are more likely to interact with the active site.
• At low temperature, the rate of reaction slows down.
• fewer collisions happen between substrates and enzymes.

Question 10

How can a change in temperature cause an enzyme to denature?

Answer 10

• When the temperature exceeds a certain temperature, the enzyme denatures
• This means that the shape of the active site on the enzyme changes shape
• The substrate molecules can no longer bind to the active site

Question 11

How does pH level have an effect on enzyme activity?

Answer 11

• the optimum range for most human enzymes is around 6-8.
• Each enzymes has its own optimum pH and they work in a narrow pH band.
• Changing the pH can alter binding at the active site.

Question 12

How can enzymes be denatured?

Answer 12

• Both extremely high temperature and extreme pH (far from optimum pH) cause reduced enzyme activity due to the enzyme denaturing
• This is when the extreme conditions break bonds in the enzyme and therefore change the structure (shape) of the protein and alter the shape of the active site
• It is therefore unable to bind to the substrate anymore

Question 13

What are Competitive Inhibitors?

Answer 13

• Competitive Inhibitors block the substrate entering the active site by binding to the active site. They mimic the shape of the substrate (complementary to the shape of some of the active site)
  = EG: Cyanide

Question 14

What are Non-Competitive Inhibitors

Answer 14

• Non-Competitve Inhibitors bind elsewhere on the enzyme and this changes the shape of the enzyme and thus reduces enzyme-substrate binding.
  EG: Lead, mercury

Question 15

How does the concentration of the substrate effect the enzyme?

Answer 15

• Increasing the concentration of the substrate increases the chance of colliding with the enzyme, therefore increasing the reaction rate
• Cannot occur forever, as then the amount of enzyme present will become a limiting factor instead.
• Increasing the concentration does not affect the reaction rate.