enzymes Flashcards
what is an enzyme made from?
globular proteins
what holds the genetic code for making an enzyme?
a gene which is a short section of DNA
what is the activation energy?
the minimum amount of energy required for a chemical reaction to occur
what is the function of an enzyme?
acts as a biological catalyst which lowers the activation energy of a reaction
what are the two hypothesis for how an enzyme catalyses a reaction?
-lock and key model
-induced fit model
describe the lock and key model?
-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.
what does the induced fit model say?
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
what does the change in the shape of the active site in the induced fit model result in?
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
what else does the induced fit model say which can make a reaction more likely to happen?
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
what is a limitation of the lock and key hypothesis?
doesn’t explain how the activation energy is lowered
what 5 factors can affect the rate of enzyme controlled reactions?
-substrate concentration
-temperature
-pH
-competitive inhibitors
-non competitive inhibitors
why does increasing substrate concentration increase rate of reaction?
more chance of collisions between enzyme’s active site and the substrate so more enzyme substrate complexes form
why does the rate not increase with further increase of substrate concentration?
number of enzymes becomes a limiting factor- all the enzymes active sites are occupied (saturated)
why does an increase in temperature increase the rate of reaction?
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
at high temperatures why do enzymes denature?
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
why do low pH values cause enzymes to denature?
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
at higher pH’s, what is the only thing to change about the explanation for enzymes denaturing?
lack of H+ ions or greater number of OH- ions
how do competitive inhibitors attach to enzymes?
they have a similar shape to the substrate and are able to bind to the active site
what does a greater number of competitive inhibitors mean?
lower chance of collisions between the substrate and the active site so lower number of ES complexes formed
even in the presence of competitive inhibitors, when might the rate still be high?
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
how do non-competitive inhibitors bind to enzymes?
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
how do non-competitive inhibitors decrease rate of reaction?
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
