enzymes

Question 1

what is an enzyme made from?

Answer 1

globular proteins

Question 2

what holds the genetic code for making an enzyme?

Answer 2

a gene which is a short section of DNA

Question 3

what is the function of an enzyme?

Answer 3

acts as a biological catalyst which lowers the activation energy of a reaction

Question 4

what is the activation energy?

Answer 4

the minimum amount of energy required for a chemical reaction to occur

Question 5

what are the two hypothesis for how an enzyme catalyses a reaction?

Answer 5

-lock and key model
-induced fit model

Question 6

describe the lock and key model?

Answer 6

-the enzymes active site is complementary to the substrate molecule
-the shape and properties of the active site are given by the amino acids around it
-these amino acids form weak hydrogen and ionic bonds with the substrate molecule, so the active site binds to one substrate only
-the formation of enzyme-substrate complexes lowers the activation energy to catalyse the reaction.

Question 7

what does the induced fit model say?

Answer 7

the enzyme is flexible and so the active site can change shape. The active site isn’t exactly complementary to the substrate, but as the substrate starts to bind, the active site changes shape to fit the substrate more closely

Question 8

what does the change in the shape of the active site in the induced fit model result in?

Answer 8

distorts the substrate molecule in he active site, making it more likely to be turned into the product.
for example, if a bond in the substrate is to be broken, the bond might be stretched by the enzyme, making it more likely to be broken

therefore, the AE is lowered

Question 9

what else does the induced fit model say which can make a reaction more likely to happen?

Answer 9

the enzyme can also make the local conditions inside the active site quite different from those outside (pH, water conc and charge) which makes the reaction more likely to happen

Question 10

what is a limitation of the lock and key hypothesis?

Answer 10

doesn’t explain how the activation energy is lowered

Question 11

what 5 factors can affect the rate of enzyme controlled reactions?

Answer 11

-substrate concentration
-temperature
-pH
-competitive inhibitors
-non competitive inhibitors

Question 12

why does increasing substrate concentration increase rate of reaction?

Answer 12

more chance of collisions between enzyme’s active site and the substrate so more enzyme substrate complexes form

Question 13

why does the rate not increase with further increase of substrate concentration?

Answer 13

number of enzymes becomes a limiting factor- all the enzymes active sites are occupied (saturated)

Question 14

why does an increase in temperature increase the rate of reaction?

Answer 14

increases kinetic energy of the molecules so there is a greater chance of collisions occurring between the enzyme’s active site and the substrate
so a greater number of ES complexes form

Question 15

at high temperatures why do enzymes denature?

Answer 15

the hydrogen bonds in the tertiary and secondary structure break so the enzyme loses its tertiary structure
the active site changes shape and is no longer complementary to the substrate. ES complexes can’t form

Question 16

why do low pH values cause enzymes to denature?

Answer 16

at pH values lower than the optimum, the greater number of H+ ions changes the charge of the enzyme, causing enzymes to lose their tertiary structure
the active sites are np longer complementary to the substrates so fewer ES complexes formed

Question 17

at higher pH’s, what is the only thing to change about the explanation for enzymes denaturing?

Answer 17

lack of H+ ions or greater number of OH- ions

Question 18

how do competitive inhibitors attach to enzymes?

Answer 18

they have a similar shape to the substrate and are able to bind to the active site

Question 19

what does a greater number of competitive inhibitors mean?

Answer 19

lower chance of collisions between the substrate and the active site so lower number of ES complexes formed

Question 20

even in the presence of competitive inhibitors, when might the rate still be high?

Answer 20

at high substrate concentrations because there is a greater chance of the substrate binding to the active site than the inhibitor so higher number of ES complexes form

Question 21

how do non-competitive inhibitors bind to enzymes?

Answer 21

they are not complementary to the active site!!
they bind to a different location on the enzyme which causes a change in the tertiary structure of the enzyme and so the active site changes shape

Question 22

how do non-competitive inhibitors decrease rate of reaction?

Answer 22

because the active site changes shape, it is no longer complementary to the substrate so fewer ES complexes form

increasing substrate conc does not bring back rate to previous level because denaturing is already done