Transcript PBHS AP Biology Lab 2

PBHS AP Biology
STEVENSON
2009-10
Lab #2: Enzyme Catalysis
 Introduction: This the first of 12 AP Labs designed to
illustrate the themes of this class. These labs are very
important as the AP Test will have least one essay question
and several multiple choice questions based on these labs.
Lab #2: Enzyme Catalysis
 Introduction
 Enzymes are proteins produced by living cells that act as catalysts in
biochemical reactions
 Substance to be acted on is called the substrate (S)
 The substrate binds reversibly to the active site of the enzyme (E)
 Reduces the energy required to activate the reaction so that products
(P) can be formed
 E + S  ES  E + P
Lab #2: Enzyme Catalysis
 Introduction
 The enzyme is not changed in any way and so can be recycled to
break additional substrate molecules
 The active site is the portion of the enzyme that reacts with the
substrate
 Any substance that blocks or changes the active site can affect the
activity of the enzyme
Lab #2: Enzyme Catalysis
 Salt concentration
 If the salt concentration is very low, the enzyme will denature and
form an inactive precipitate
 If the salt concentration is very high, new interactions will occur and
again an inactive precipitate is formed
 Intermediate salt concentrations such as human blood (0.9%) is the
optimum for many enzymes
Lab #2: Enzyme Catalysis
 pH
 As the pH is lowered (solution becomes acidic), the side chains will
attract H+ ions and the enzymes shape is disrupted
 As the pH goes up, the enzyme will lose H+ ions and again, the
shaped is altered
 Optimum pH is in the neutral range
 At very low or high pH, the enzyme denatures (breaks down)
Lab #2: Enzyme Catalysis
 Temperature
 Increasing temperature cause enzyme reactions to go faster… up to a
point
 At very high temps, the enzymes structure is broken down
 Many enzymes function well up to 40-50 C, and some are active up
to 70-80 C
Lab #2: Enzyme Catalysis
 Activators and Inhibitors
 Many molecules other than the substrate may interact with an
enzyme
 If such a molecule increases the rate of reaction, it is called an
activator; if it decreases the rate of reaction, it is an inhibitor
 Many well know poisons such as potassium cyanide and curare are
inhibitors that interfere with the active sites of critical enzymes
Lab #2: Enzyme Catalysis
 Lab #2
 The enzyme used in this lab is catalase
 Catalase has 4 polypeptide chains, each composed of more than 500
amino acids
 One fucntion of catalase is