Book 3- enzymes

Question 1

What are enzymes?

Answer 1

biological catalysts enabling chemical reactions to take place in a cell at relatively low temperatures. They are not used up, just lower the activation energy

Question 2

Explain the structure of proteins?

Answer 2

• globular proteins
• made up of amino acids joined together by peptide bonds forming a primary structure
• that is then folded into secondary structures then further into tertiary
• hydrogen, ionic and disulphide bonds hold the structure in place

Question 3

How do enzymes function?

Answer 3

Enzymes have a specific tertiary structure, so have a specific active site that only complementary substrate can bind to. This forms an ES complex. Bonds in the substrate are either made or broken (condensation/hydrolysis reactions). The products are then released from the active site and the enzyme is free to take part in further reactions.

Question 4

What is the lock and key theory?

Answer 4

this theory describes how the enzyme’s active site has a fixed shape. The active site is complementary before and after the substrate binds as the active site shape does not change shape.

Question 5

What is the induced fit theory?

Answer 5

the active site is not complementary shape to the substrate. as the substrate moves into the active site, the active site shape changes and becomes complementary to the substrate.

Question 6

What factors effect the rate of reaction?

Answer 6

enzyme conc, substrate conc, temperature, pH, inhibitrs

Question 7

How does the enzyme conc affect the rate of reaction?

Answer 7

As the conc increases, the rate increases because more and more ES complexes form as more enzymes are added. Eventually the reaction would stop as the substrate would run out.

Question 8

How does the substrate conc affect the rate of reaction?

Answer 8

rate increases as more ES complexes form. the rate slows down to a constant rate as all active sites have been occupied by substrate molecules.

Question 9

How does the temperature affect the rate of reaction?

Answer 9

The rate increases as temp does because:
- enzyme substrate molecules have more kinetic
- move around faster making more collisions
- forming more ES complexes
As the temp rises above optimum temp, rate decreases because:
- enzyms denature
-breaking H and ionic bonds
-tertiary structure changes
-no longer complementary

Question 10

How does the pH affect the rate of reaction?

Answer 10

variations from optimum can result in denatured enzymes. ph measures the H bonds, which forms the tertiary structure. a change causes a change in the structure so its no longer complementary.

Question 11

Explain how competitive inhibitors work?

Answer 11

• The inhibitor is similar shape to the substrate.
• inhibitor binds to the active site, it prevents the substrate from binding to the active site.
• Some ES substrates will form but at a much slower rate.

Question 12

What do inhibitors do?

Answer 12

reduce the rate of reaction

Question 13

Explain how non-competitive inhibitors work?

Answer 13

• the inhibitor is different to the substrate
• inhibitor attaches to a binding site on the enzyme molecule away from the active site
• this causes the hydrogen and ionic bonds in the enzyme to break, causing the tertiary structure and active site to change.
• substrate is no longer complementary to the active site so doesn’t bind.
• ES complexes cannot form