Enzymes

Question 1

what are enzymes?

Answer 1

enzymes are globular proteins
enzymes are specific
refer to active sites if you are talking about how enzymes work/ denature/ anything binding to them/ function
e.g. substrates are complementary ij shape to active sites not enzymes
talking about enzyme substrate complexes (ESC”S) forming/ not forming will usually get marks
mentioning lock and key hypothesis/ induced fit hypothesis get marks when talking about enzyme action

Question 2

why enzymes are known as specific

Answer 2

• shape of the active site
• complementary
• to correct substrate
• will form ESC
• any other substrate will not

Question 3

enzyme action

Answer 3

• as the substrate binds to the active site, the enzyme changes shape slightly
• the active site is tighter around the substrate molecules
• oppositely charged groups on the substrate and active site interact and hold the substrate molecule in place. this the ESC
  the enzymes shape change puts strain on bonds in the substrate which destabilises it
  the products is formed (enzyme product complex) and because it is different shape to the reactant it is released from the active site.

Question 4

explaining the effect of temperature on enzyme activity

Answer 4

• to and at optimum:
  as molecules are heated they gain kinetic energy and move around faster - this results In more frequent collisions
• this results in more enzyme substrate complexes and therefore a higher (Max) rate of reaction and more product is formed.

above optimum:
- molecules have more kinetic energy
- enzymes vibrate too much and weaker bonds are broken (ionic and hydrogen)
the tetra structure of the enzymes are changed
this means that the active site loses complementary shape
- no ESC’s formed as substrate doesn’t fit into the active site
- NO ESC’S can form = no product = no reaction
enzymes are denatured at extremes of PH (for that enzyme).

at optimum:
- the concentration of hydrogen ions gives the tietry structure the best shape = most complementary active site.

Question 5

explaining the effect of increasing enzyme concentration on enzyme activity (fixed concentration of substrate)

Answer 5

as long as the substrate is in excess:

• as enzyme conc. increase, reaction rate increases
• more enzymes = more active sites = more ESC’S formed so more product also = higher rate of reaction

as the substrate is used up/ not in excess
when substrate is used up the ROR will decrease as less product is formed
substrate is limiting

Question 6

effect of substrate concentration - enzyme activity

Answer 6

as long as the enzymes are in excess:
as substrate conc. increases rate of reaction increases
more substrate = more frequent Collisions between active sites and substrate = more ESC’s = more product = higher rate.

when all the active sites are occupied:

• it is not possible for more ESC’s to from at any one time = increasing the substrate conc - rate plateaus has no further affect on rate of reaction.
• the enzyme conc. is a limiting factor.

Question 7

what is a competitive inhibitor?

Answer 7

CI - similar shapes to enzymes substrates
their shape is complementary to active site soothes can bind with it and block it.
this prevents ESC’s forming and slows rate of reaction - no products can be formed
do not bind perminately to the active site - action Is reversible.

Question 8

explaining the effect of competitive inhibitor on enzyme activity

Answer 8

rate determine by relative conc. of substrate and inhibitor
more inhibition if substrate conc. is lower than inhibitor conc.
there is a higher chance of inhibitor entering active site than substrate = less ESC’s = less effects can be reversed by increasing substrate conc.

Question 9

what are non-competitive inhibitors

Answer 9

Alloristic site of enzyme
alters the tietry structure of the enzyme and changes the shape of the active site
this means that the substrate can no longer fit into the active site so no ESC”S form - rate of reaction decreases
bind perminately to enzymes - their effect is irreversible the enzymes become useless

Question 10

explaining the effect of non-competitive inhibitor conc. on enzyme activity

Answer 10

increasing substrate conc. had no effect on the rate because it will bind irreversibly - if all enzymes have a non-competitive inhibitor bound the reaction will stop
changing the conc of inhibitors will reduce the rate further = fewer ESC’S = less product