enzymes

Question 1

what are enzymes

Answer 1

-tertiary structure proteins that catalyse reactions

Question 2

why is the active site specific and unique

Answer 2

because of the specific folding and bonding in the tertiary structure of the protein

Question 3

how do enzymes speed up reaction

Answer 3

lowering the activation energy by binding to (substrate) + allowing chemical bond-breaking and bond-forming processes to happen more easily

Question 4

factors affect enzyme activity

Answer 4

-temperature
-pH
-substrate concentration
-enzyme concentration
-inhibitors

Question 5

temperature

Answer 5

-if temp is too low, there is not enough KE for successful collisions between enzyme + substrate molecules—> fewer enzyme substrate complexes

-if above optimum , temp is too high –> enzyme denatures + active site changes shape —> enzyme substrate complexes cannot form

-bonds holding the amino acid in their fixed 3D tertiary structure in the active site are going to be broken because of the increase in temp.

Question 6

pH

Answer 6

• high pH: too many H+ ion
  -low pH; too many OH- ions

+ and - charge interferes with the charges in the amino acid within the active site
- bonds holding the amino acid together in their fixed 3D shape will break (mainly hydrogen + ionic bonds)

-shape of the active site will change , enzyme denatures + there is fewer substrate complexes

Question 7

substrate concentration

Answer 7

-as the substrate concentration increases the rate of reaction increases
-more substrate molecules means more frequent collisions between substrate and enzyme and so more active site is occupied

-at the saturation point : all active sites are occupied

• beyond saturation point - there is too many substrate molecules so all active sites are occupied and there are spare substrate molecules

Question 8

enzyme concentration

Answer 8

increasing enzyme concentration, increases the rate of reaction
- more likely for substrate molecules to collide with enzymes and form enzyme substrate complexes

• if the amount of substrate is insufficient – the reaction will be slower as there is fewer collisions between the enzyme and substrate

Question 9

competitive inhibitor

Answer 9

Competitive inhibitors have a similar shape to that of the substrate molecules and therefore compete with the substrate for the active site

• the greater the substrate concentration, the substrate out-competes the inhibitor for the active site

Question 10

A competitive inhibitor decreases the rate of an enzyme-controlled reaction.
Explain how.

Answer 10

1. Inhibitor similar shape to substrate;
2. Fits/binds to active site;
3. Prevents/reduces enzyme-substrate complex forming;

Question 11

non competitive inhibitor

Answer 11

binds to the enzyme at an allosteric site

increasing the substrate concentration cannot increase the rate of reaction once more, as the shape of the active site of the enzyme remains changed and enzyme-substrate complexes are still unable to form

Question 12

Describe the induced-fit model of enzyme action and how an enzyme acts
as a catalyst.

Answer 12

-Substrate binds to the active site/enzyme
-Active site changes shape (slightly) so it is complementary to
substrate
-. Reduces activation energy;

Question 13

describe the lock and key model

Answer 13

-enzymes active site is fixed shape
-due to the random collisions, substrate can collide and attach to the enzyme forming an enzyme substrate complex

-once the enzyme substrate complex is formed causes the substrate shape to slightly distort thus lowering the activation energy

-products are released + enzyme is re used