Download Enzymes

Enzymes
Catalysts speed up the rate of a reaction without being used up
A + B C, where A and B are reactants and C is the
product.
An example is MnO2
Enzymes are biological catalysts that are proteins (composed of
amino acids). They are globular in shape.
Names end in –ase—
Catalase—2H2O2 2H2O + O2
Arginase—arginine + 2H2O urea + ornithine
They work under physiological conditions (w/in the
constraints of the cells and the organism)
-- body temperature 37° C
if temp. too low—slow reaction
if temp. too high—denature enzyme
-- physiological pH of 7
(too high, low denature enzyme)
--- salt and metal concentration w/in cell
--- substrate (a reactant converted to product by
enzyme) concentration w/in cell
Enzyme works by using an active site, which binds the
substrate (the reactant) so that through catalysis a
product is formed. It is not used up in the reaction.
Active Site
Enzyme
Enzyme
Substrate
product
Enzymes are very specific for a substrate—geometry/shape,
charge, hydrophobicity. In above example, a substrate with a
triangular or circular shape would not fit into the active site &
therefore no product made.
It also lowers the amount of energy required to covert the
substrate to a product (as compared to an uncatalyzed
reaction)
Transition State
Transition State
S
P
G, free energy
G, free energy
Activation energy
S
Lower Activation
Energy
P
Enzymes can be poisoned or inhibited so can’t convert substrate to
product—
Poisoning permanently alters active site—heavy metals
(cyanide, arsenic)
Inhibition is temporary by binding to active site—ether
chloroform; uses as anesthesia.
Today: Studying the enzyme catalase, which speeds up the
following reaction-2H2O2 2 H2O + O2 (bubbles in vitro)
I)
Testing for catalase presence in various tissues (animal vs.
plant)
II) Effects of Temperature on catalase’s activity
III) Effects of pH on catalase’s activity
IV) Testing another feature of enzymes—what are we testing?
Please help w/ clean up! Many thanks!