State Standard
SB1B - Explain how enzymes act as
catalysts.
Chapter 6
Chemistry in Biology
6.2 Chemical Reactions
Physical vs. Chemical
 A physical change alters the
substance’s appearance but
not its composition.
 There is no formation of a new
substance.
Physical reaction
Chapter 6
Chemistry in Biology
6.2 Chemical Reactions
Physical vs. Chemical Cont’d
 A chemical reaction is the
process by which atoms or
groups of atoms in substances
are reorganized into different
substances.
 Clues that a chemical
reaction has taken place
include the production of
heat or light, and formation
of a gas, liquid, or solid.
 Not reversible!
Chemical reaction
Chapter 6
Chemistry in Biology
6.2 Chemical Reactions
Chemical Equations
 Chemical formulas describe the substances in
the reaction and arrows indicate the process of
change.
 Chemical equations have 2 sides:
 Reactants are the starting substances, on the
left side of the arrow.
 Products are the substances formed during
the reaction, on the right side of the arrow.
Chapter 6
Chemistry in Biology
6.2 Chemical Reactions
Chemical Equations Cont’d
 Example of a chemical equation: During
cellular respiration, Glucose and oxygen
react to form carbon dioxide and water.
Practice your knowledge by labeling the parts of the equation above.
Chapter 6
Chemistry in Biology
6.2 Chemical Reactions
Energy of Reactions
 The activation
energy is the
minimum amount of
energy needed for
reactants to form
products in a
chemical reaction.
Chapter 6
Chemistry in Biology
6.2 Chemical Reactions
Enzymes
 A catalyst is a
substance that lowers
the activation energy
needed to start a
chemical reaction.
 It does not increase how
much product is made – only how quickly it is
made.
 Enzymes are proteins that act as biological
catalysts.
Chapter 6
Chemistry in Biology
6.2 Chemical Reactions
Enzymes Cont’d
 All living things are driven by constant internal
chemical reactions (metabolism).
 Enzymes help these reactions happen quickly
enough for an organism to stay alive.
 Enzymes increase the rate (speed) of a reaction by
lowering activation energy.
Chapter 6
Chemistry in Biology
6.2 Chemical Reactions
Enzymes Cont’d
 The reactants that bind to the enzyme are called
substrates.
 The specific location where a substrate binds on an
enzyme is called the active site.
Chapter 6
Chemistry in Biology
6.2 Chemical Reactions
Enzymes Cont’d
 The active site changes shape and forms the
enzyme-substrate complex, which helps
chemical bonds in the reactants to be broken
and new bonds to form. This is called induced
fit.
Chapter 6
Chemistry in Biology
6.2 Chemical Reactions
Enzymes Cont’d
 Enzyme activity is
affected by factors such
as pH, temperature, &
other substances.
 Extreme pH &
temperature can change
the shape of the enzyme
and render it useless.
This is called
denaturing.
Chapter 6
Chemistry in Biology
6.2 Chemical Reactions
Enzymes Cont’d
 Enzymes are named for the substrates that they
react with…
 Enzyme names end with the suffix “-ase”.
 Examples:
 Sucrase breakes down the sugar sucrose
 Lactase breaks down the sugar lactose
 Protease breaks down protein molecules
Chapter 6
Chemistry in Biology
6.2 Chemical Reactions
Enzymes Cont’d
 Enzyme action is often compared to the action of
locks & keys…
…because each enzyme is
shaped to fit together with a
specific substrate and they
are reusable.
Chapter 6
Chemistry in Biology
Chapter 6
Chemistry in Biology
Chapter Diagnostic
Questions
Identify the proteins that speed up the rate of
chemical reactions.
A. substrates
B. enzymes
C. ions
D. reactants
Chapter 6
Chemistry in Biology
6.2 Formative
Questions
Which is a chemical reaction?
A. a match burning
B. salt dissolving
C. water boiling
D. gasoline evaporating
Chapter 6
Chemistry in Biology
6.2 Formative
Questions
How does an enzyme increase the rate of a
chemical reaction?
A. It acts as a reactant.
B. It reduces the amount of heat produced.
C. It increases the amount of product.
D. It lowers the activation energy.
Chapter 6
Chemistry in Biology
6.2 Formative
Questions
What occurs at the active site in the
enzyme substrate complex?
Chapter 6
Chemistry in Biology
6.2 Formative
Questions
A. An exothermic chemical reaction takes
place.
B. Chemical bonds are broken and new
bonds are formed.
C. The enzyme gets used up in the
reaction.
D. The substrates provide energy for the
enzyme.
Chapter 6
Chemistry in Biology
6.4 Formative
Questions
What type of biological molecule is an
enzyme?
A. hormone
B. nucleic acid
C. protein
D. steroid
Chapter 6
Chemistry in Biology
Chapter Assessment
Questions
Look at the following figure. Determine what
the upward curve represents.
A. activation energy
B. reactants
C. products
D. enzymes
?