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 function of an enzyme?
acts as a biological catalyst which lowers the activation energy of a reaction
what is the activation energy?
the minimum amount of energy required for a chemical reaction to occur
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)
