• Have you ever sat around a campfire or watched flames flicker in a
fireplace? The burning of wood is a chemical reaction—a process that
changes one set of chemicals into another set of chemicals. A
chemical reaction always involves changes in chemical bonds that join
atoms in compounds. The elements or compounds that enter into a
chemical reaction are called reactants. The elements or compounds
produced by a chemical reaction are called products. As wood burns,
molecules of cellulose are broken down and combine with oxygen to
form carbon dioxide and water vapor, and energy is released.
•
1. What are the reactants when wood burns?
•
2. What are the products when wood burns?
•
3. What kinds of energy are given off when wood burns?
•
4. Wood doesn’t burn all by itself. What must you do to start a fire? What does this
mean in terms of energy?
•
5. Once the fire gets started, it keeps burning. Why don’t you need to keep restarting
the fire?
Concept Map of Organic Compounds
Section 2-3
*Fill in the Blanks*
Carbon
Compounds
include
that consist of
that consist of
that consist of
that consist of
which contain
which contain
which contain
which contain
Concept Map of Organic Compounds
Section 2-3
*Answer Key*
Carbon
Compounds
include
Carbohydrates
Lipids
Nucleic acids
Proteins
that consist of
that consist of
that consist of
that consist of
Sugars and
starches
Fats and oils
Nucleotides
Amino Acids
which contain
which contain
Carbon,
hydrogen,
oxygen
Carbon,
hydrogen,
oxygen
which contain
which contain
Carbon,hydrogen,
oxygen, nitrogen,
phosphorus
Carbon,
hydrogen,oxygen,
nitrogen,
Chemical
reactions and
Enzymes
Chapter 2.4
Chemical Reactions
• Chemical reaction –
a process that changes one set of chemicals
into another set of chemicals
ex. Iron and oxygen combine to form iron
oxide or rust
• Always involve changes in the chemical
bonds that join atoms in compounds
Chemical Reactions
• The elements or compounds that enter
into a chemical reaction are known as
 reactants
• The elements or compounds produced by
a chemical reaction are known as
products
Energy in reactions
• Bonds are the storage place of energy in
molecules / compounds
– Break a bond  release energy
– Make a bond  store energy
Energy in Reactions
• Chemical reactions that release energy often
occur spontaneously
• Chemical reactions that absorb energy
– will not occur without a source of energy
• All living things carry out energy-needing
reactions
– All have their own source of energy
• Sun
• Chemicals
• food
Energy in Reactions
Energy-Absorbing Reaction
Products
Activation energy
Reactants
Energy-Releasing Reaction
Energy in Reactions
Energy-Absorbing Reaction
Energy-Releasing Reaction
Activation
energy
Products
Activation energy
Reactants
Reactants
Products
Activation energy
energy needed to get a reaction started
• Required whether energy is released or
absorbed.
Enzymes
• Catalyst –
 A substance that speeds up the rate of a
chemical reaction
– Lowers the reaction’s activation energy
• Biological catalysts = enzymes
Enzymes
• Living cells use enzymes to speed up
virtually every important chemical reaction
that takes place inside cells
• Lowers the activation energy required for
the reaction to occur thereby increasing
the rate in which the reaction takes place.
Reaction pathway
without enzyme
Reactants
Reaction pathway
with enzyme
Activation energy
without enzyme
Activation
energy
with enzyme
Products
Review
• What is the difference between the
reactant and a product? Give an example
• How is energy released and stored within
a chemical compound?
• Does both energy absorbing and energy
releasing reactions require activation
energy? What is activation energy?
• What is one benefit to a catalyst?
Enzyme Example
• Cells release carbon dioxide into the blood
– Carbon dioxide will not dissolve in blood
• Reacts with water to become carbonic acid which
is soluble in blood
– When carbonic acid gets to lungs, converts
back to carbon dioxide
Enzyme Example
• Left by itself, reaction probably would not
take place fast enough to remove carbon
dioxide from our body
– We would die
• Enzyme (carbonic anhydrase)
– Speeds up reaction 10 million times
Enzyme Specificity
• Enzymes are very specific
catalyze only one chemical reaction
• Part of the name of the enzyme is derived
from the reaction it catalyzes
– Carbonic anhydrase removes water from
carbonic acid
Enzyme Action
• If enzymes are not present, reactants must
randomly collide with one another with
enough energy to make products
• Enzymes make process faster and easier
by getting involved in reactions
Enzyme action
• Substrates
the reactants of an enzyme-catalyzed
reactions
• Bind to enzyme at active site
– Form enzyme-substrate complex
– Very specific – like a lock & key
Enzyme action
• Once complex is formed, enzyme does its
job of making products of reaction
– Products are released
– Enzymes go to bind with new substrates (they
are recycled)
– P. 52 Figure 2-21
Enzyme Action
Enzyme action
Enzyme action is very sensitive to
environmental conditions
pH
temperature
Enzymes play an essential role in
regulating chemical pathways
making materials cells need
releasing energy
transferring information