Biological Molecules: Enzymes

Question 1

what are enzymes?

Answer 1

• globular proteins
• biological catalysts
• 3D tertiary structure

Question 2

how do enzymes catalyse a reaction?

Answer 2

lowers the activation energy

Question 3

why are enzymes highly specific?

Answer 3

tertiary structure

Question 4

where do enzymes work?

Answer 4

• at a cellular level to the whole organism

Question 5

what types of reactions do enzymes catalyse(wide range)?

Answer 5

• intracellular: e.g. photosynthesis and respiration
• extracellular: e.g. salivary amylase, pepsin

Question 6

explain the induced fit model of enzyme action.

Answer 6

• substrate binds to the active site, ESC forms
• as the substrate binds the active site changes shape slightly so that it is complementary to the substrate

Question 7

what are the properties of enzymes related to?

Answer 7

• its tertiary structure

Question 8

what are the properties of enzymes?

Answer 8

• they are specific and only catalyse one reaction

Question 9

why are enzymes specific?

Answer 9

only one complementary substrate will bind to the active site

Question 10

what happens if the substrate shape isn’t complementary to the active site?

Answer 10

no ESC is formed, thus the reaction isn’t catalysed

Question 10

what determines the shape of the active site?

Answer 10

the tertiary structure (and this is determined by primary structure)

Question 11

why do enzymes differ?

Answer 11

• each different enzyme has a different tertiary structure so different shaped active site

Question 12

what could cause changes to an enzyme and its active site?

Answer 12

• alteration of the tertiary structure (can be caused by a change in pH or temperature)
• primary structure of a protein is determined by a gene, and if a mutation occurs in that gene, the tertiary structure of the enzyme produced changes

Question 13

what factors affect the rate of enzyme-controlled reactions?

Answer 13

• enzyme concentration
• substrate concentration
• concentration of competitive and non- competitive inhibitors
• pH
• temperature

Question 14

how does enzyme concentration affect the rate of enzyme-controlled reactions?

Answer 14

• increasing enzyme concentration, increases ROR
• more enzyme molecules in a solution = more likely substrate molecule is to bind with one and form ESC
• if substrate is limited then adding more enzymes would have no effect at some point

Question 15

how does substrate concentration affect the rate of enzyme-controlled reactions?

Answer 15

• higher the substrate concentration, faster the reaction = more substrate molecules that are available to bind to the active site
• this occurs until the saturation point , after that there are too many substrate molecules and all the active sites are occupied

Question 16

how does temperature affect the rate of enzyme-controlled reactions?

Answer 16

• rate of enzyme-controlled reactions increases as temperature increases
• higher temps = more kinetic energy = faster reactions
• ESC forms at faster rates
• at higher temps the enzyme denatures

Question 17

how does pH affect the rate of enzyme-controlled reactions?

Answer 17

• all enzymes have different optimum temperatures
• above or below the optimum pH, the H+ or OH- ions found in acids and alkalis disrupt the ionic bonds and hydrogen bonds that hold enzymes tertiary structure in place
• thus the enzyme becomes denatured and the active site changes shape

Question 18

how does competitive inhibitors affect the rate of enzyme-controlled reactions?

Answer 18

• they compete with the substrate molecules as they are similar shapes and bind to the active site
• this reduces the forming of ESC

Question 19

what is a competitive inhibitor?

Answer 19

• molecules with a similar shape to that of substrate molecules

Question 20

what are non-competitive inhibitors?

Answer 20

• molecules which bind to the enzyme away from its active site

Question 21

how does non-competitive inhibitors affect the rate of enzyme-controlled reactions?

Answer 21

• non-competitive inhibitors bind away from the active site and this causes the shape of the active site to change so substrate molecule no longer binds to it
• prevent ESC forming

Question 22

what are the models of enzyme action?

Answer 22

• induced-fit model
• lock and key model

Question 23

what is the lock and key model?

Answer 23

• substrate binds to active site of enzyme as they are complementary to each other
• ESC forms
• chemical reaction takes place and products are formed

Question 24

what is the difference between the lock and key model and the induced fit model?

Answer 24

the lock and key model suggests that the enzyme is unchanged after the reaction whereas the induced fit model suggests that the enzyme changes shape slightly