1.4 Enzymes

Question 1

what is an enzyme

Answer 1

they are biological catalysts, meaning they are proteins that speed up the rate of reaction without changing the substances produces, they also remain unaffected at the end of the reaction

Question 2

describe the structure of an enzyme

Answer 2

• globular protein
• specific shape as a result of their primary, secondary… etc. structure

Question 3

which factors affect the efficiency of an enzyme and why

Answer 3

• changes in temperature
• changes in pH
  they affect the intramolecular bonds within the protein that are responsible for the shape of the specific active site

Question 4

what’d the difference between intracellular and extracellular enzymes, and give an example of each

Answer 4

Intracellular - work inside the cell, DNA polymerase, DNA ligase
Extracellular - enzymes that have an effect beyond the cell bebmbrane, lysozyme

Question 5

what is the lock and key hypothesis

Answer 5

• the idea that the active site of an enzyme is a very specific shape, only one substrate or type of substrate will fit into the shape
• this is what gives the enzyme its specificity
• just as a key fits in a lock to form a complex

Question 6

how do enzymes catalyse a reaction

Answer 6

• The substrate binds to the active site of the enzyme, and the formation of an enzyme substrate complex lowers the activation energy of the reaction
• The active site affects the bonds in the substrate, making it easier for them to break and the reactants are brought closer together making it easier for the bonds to break
• products form and are released from the active site

Question 7

when measuring the rate of enzyme activity, explain what must be controlled? and how do you control it?

Answer 7

1. Temperature
   - use a water bath to keep temperature constant
   -because enzymes can become denatured or increase in kinetic energy will increase the amount of successful collisions
2. pH
   - use a buffer
   - pH affects the shape of the active site and therefore the rate of reaction
3. concentrations of solutions
   - use a measuring cylinder to measure out volumes
   - concentration will affect the rate of reaction due to increase in frequency of collisions between enzyme and active site

Question 8

why is the initial rate of enzyme activity important

Answer 8

• because it is when the reaction proceeds at its fastest rate
• this gives the maximum reaction rate for an enzyme under particular conditions

Question 9

how are enzymes affected by the following:
- competitive inhibition
- non-competitive inhibition

Answer 9

1. COMPETITIVE INHIBITION
   - the inhibitor molecule is a similar shape to the substrate molecule
   - competes with the substrate to bind to enzymes active site to form ES complex
   2 NON-COMPETITIVE INHIBITION
   - enzyme forms a complex with enzyme or the ES complex, binds to a place that is NOT the active site
   - after binding, changes the shape of the active site so can no longer catalyse reactions

Question 10

what are some poisonous enzyme inhibitors and why are they so poisonous

Answer 10

• arsenic, cyanide, mercury
• all poisonous because they bind irreversibly to enzymes

Question 11

what is end product inhibition

Answer 11

• it is the way that a lot of the complex metabolic reactions in the cell are are controlled
• the end product of a metabolic pathway e.g. respiration, ATP will bind to a regulatory enzyme non-competitively that’s involved in ATP production
• this changes the shape of the active site
• if the end product concentration goes up, then more will bind to the enzyme and inhibit the reaction
• if the end product concentration goes down, more end product will be released from enzymes and the enzymes become active again