1.4-Enzymes Flashcards
Define enzyme?
-are protein
-are tertiary structure proteins and so they are a very specific 3D shape.
-This includes an active site which is held together
by peptide, hydrogen, ionic and disulphide bonds.
Define catalyst?
-Speed up rate of reaction
-lower activation energy
-remains unchanged in reaction.
Define intracellular enzyme?
These work inside cells.
Define Extracellular enzyme?
are secreted from cells for use outside of the cell.
lock and key theory?
-enzymes are specific to one type of substrate as they have an active site has a complementary shape into one of substrate forming an
enzyme-substrate complex.
-The reaction occurs and the products are released.
-The enzyme remains unchanged at the end of the reaction.
Induced fit theory?
-lysozyme is
proposed to function in this way.
-the active site and substrate are not
fully complementary in shape. Reactive groups in these areas align and the substrate forces its way into the active site. Both areas change structure slightly, the bonds in the
substrate weakens and the reaction occurs at a lower activation energy.
Metabolism – anabolic reactions:
(building up molecules).
catabolic reactions:
(breaking down molecules) that are catalysed by enzymes.
Activation energy? graph
-Enzymes are catalysts, which means they lower the activation energy of reactions but remain unchanged in the reaction.
Factors affecting enzymes, Temperature?
-At low temperatures, there is low kinetic energy
and so few successful collisions where the substrate is able to enter the active site of the enzyme and form products.
-As the temperature increases, the kinetic
energy increases and so there are more collisions and enzyme-substrate complexes formed per unit time leading to increased
product. This continues up to an optimum
temperature.
-If the temperature continues to increase, the kinetic energy increases to a point where vibrations in the enzyme molecule weaken some bonds holding the 3D tertiary
structure of the active site together.
-The active site loses its shape,
-the substrate is no longer complementary to the active site,
-no further enzyme-substrate complexes can
be made,
-and the enzyme is said to be denatured(change shape).
Substrate concentration?
-As enzyme reaction relies on successful collisions between enzymes, any increase in the substrate concentration will increase
collisions and the rate of reaction. Therefore, at low substrate concentrations, it is this factor that is limiting the rate of reaction
as increasing the substrate concentration
increases the rate of reaction.
-At some point
though, any further increase in substrate
concentration has no effect on the rate of
reaction.
-It is no longer the limiting factor. The rate of reaction plateaus as all the
enzymes have full active sites at any one
time.
-The enzyme concentration is the limiting factor now.
PH?
-Most enzymes have an optimum pH. Small changes from the optimum, either above or
below optimum pH, make small reversible changes in the enzyme molecule reducing its efficiency. Large changes in pH can
disrupt ionic and hydrogen bonds in the enzyme causing permanent changes to the shape of the active site. This prevents the formation of enzyme-substrate complexes, denaturing the enzyme.
Non-competitive inhibitors ?
-bind to the enzyme away from the active site at an
‘allosteric’ site. This alters the shape of the active site so no enzyme-substrate
complexes can be formed. Some inhibitors bind reversibly, while others
bind irreversibly
Enzyme concentration?
-Assuming an excess of substrate, any increase in enzyme concentration increases the rate of reaction as more active sites are available for reactions.
Competitive inhibitors?
are complementary in shape to the active site of the enzyme. They therefore prevent the formation of enzyme substrate complexes by blocking the active site. They do not bind permanently.
