2-3 Carbon Based Molecules
Carbon atoms are the basis of most molecules that
make up living organisms.
Organic molecules contain carbon atoms bonded to
carbon and other atoms.
Carbon is so important because its atomic structure
gives it bonding properties that are unique.
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Each carbon has four electrons in its
outer energy level.
 So carbon can form covalent bonds
 with up to four other atoms, including
carbon atoms.
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Carbon based molecules can form:
Straight chains
 Branched chains
 Rings

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Branched
straight
ring
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
The smaller molecules can form very
large, very complex molecules..
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A Monomer is a small complete molecule
(mono= one)
 Monomers join to form polymers.
 Polymers are large molecules or
macromolecules,
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There are Four major carbon-based
(organic) macromolecules:
 Carbohydrates
 Lipids
 Proteins and
 Nucleic acids
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Carbohydrates
Are made of C, H, & O on a 1:2: 1 ratio.
 (example: glucose: C6H12O6 )
 They are sugars and starches, they
provide energy for cells and the structure
in plant cells.
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Monosaccharides are simple sugarsfructose & glucose are examples.
 Monosaccharides can be joined to make
disaccharides like sucrose (table sugar)
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
Many monosaccharides can be joined to
make polysaccharides.
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Animals store glucose as glycogen.
 Plants store glucose as starch.
 Cellulose makes up the cell walls of Plant
cells- the fibers in plants.
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Lipids (fats)
Lipids are nonpolar molecules- fats, oils &
cholesterol.
 Lipids contain C, O, & H. Some lipids
can be broken down for energy, others
provide structure for the cell.

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Lipids contain the highest amount of
energy per gram.
 they contain a glycerol molecule bonded
to fatty acids.
 Fatty acids are long chains of carbons
bonded to hydrogens.
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
Saturated Fats have the maximum number
of hydrogen atoms possible. They are
“saturated” with hydrogen atoms in single
bonds. Animal fats- they can build up in
the blood vessels.
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
Unsaturated Fats- have some double
bonds, so they are not “saturated” with
hydrogen. Fats from plants. They do not
build up in the blood vessels because of
the different structure.
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Phospholipids- are glycerols with a
 phosphate “head” and two fatty acid tails

They form the phospholipid bilayer of the
cell membrane.
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
Cholesterol based steroids have a ring
shape. They are used to make steroid
hormones such as testosterone and
estrogen.
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Proteins
Proteins are made of monomers called
amino acids.
 There are 20 different amino acids

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Amino acid structure: A central C
surrounded by:
 1. A hydrogen
 2. an amino group (NH2)
 3. a carboxyl group (COOH)
 4. an R group

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
The R group is different for each amino
acid.The are 20 R groups.
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Amino acids are bonded together by
peptide bonds.
 Polypeptides- a chain of amino acids held
together by peptide bonds.
 Polypeptide = Protein

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Proteins differ in the number and order
of amino acids.
 The specific amino acid sequence
determines the proteins structure and
function.
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Proteins fold up into 3- dimensional
shapes.
 Just one change in an amino acid
sequence can change the structure and
change the function.
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Nucleic Acids

DNA & RNA
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
The monomers are nucleotides.
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
DNA stores information to assemble
amino acids into proteins and RNA helps
build proteins.
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Structure:
 1. a phosphate
 2. a 5 carbon sugar
 3. a nitrogen base

DNA- 4 bases: A,T,C,G.
 RNA- 4 bases: A,U,C,G.
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2-4 Chemical Reactions

Chemical reactions change substances
into different substances by breaking and
forming chemical bonds.
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Reactants are the substances changed
during a chemical reaction.
 Products are the substances formed
during a chemical reaction.


C6H12O6 + 6O2 → 6CO2 + 6 H2O + Energy

reactants
products
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Bond energy is the amount of energy that
will break a bond between two atoms.
 Bonds between different atoms have
different bond energy.
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Chemical Equilibrium
 Many reactions in organisms are
reversible- they move in both directions


When a reaction takes place at an equal
rate it is at equilibrium.
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All chemical reactions involve changes in
energy.
 Energy is both absorbed and released
during chemical reactions. Some reactions
release more energy, some absorb more
energy.
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
Activation energy is the amount of energy
needed (absorbed) to start a reaction.
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
An Exothermic reaction releases more
energy than it absorbs. The products have
a lower bond energy than the reactants.
Sometimes the energy is given off as heat
or as light.(Bioluminescence.)
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
An Endothermic reaction absorbs more
energy than it releases. The products have
a higher bond energy than the reactants.
Photosynthesis is endothermic, energy is
stored as carbohydrates.
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2-5 Enzymes
Activation Energy for a reaction may be
very high or the reaction may proceed
very slowly.
 A Catalyst is a substance that decreases
the activation energy needed to start a
reaction.
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
Because a catalyst is present, less energy
is needed, so the reaction proceeds at a
faster rate.
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Enzymes are catalysts for living things –
Biological catalysts.
 Most enzymes are proteins – long chains
of amino acids.
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Enzymes are very specific- the
temperature and pH can affect the
structure and function of the enzyme.
 Enzymes specific structure allow it to
work on a specific molecule.
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The substrate is the reactant an enzyme
works on. The enzyme and substrate fit
together at the active site. (like a lock
and key)
 The enzyme weakens the bonds, and the
reaction occurs.
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
Enzymes are not used up by the reaction,
but can be used over and over again.
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