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Lipids
• A fat consists of a three-carbon backbone
called glycerol attached to three fatty acids,
which contain long hydrocarbon chains.
• Some fats are solid at room temperature.
Other fats called oils are liquids at room
temperature.
• In addition to storing energy for later use,
fatty tissues cushion your organs and
provide your body with insulation.
A saturated fat is a fat in which all three
fatty acid chains contain the maximum
possible number of hydrogen atoms.
All the carbon atoms in the fatty acid
chains form single bonds with each other,
and the rest of their bonds are with
hydrogen atoms.
Most animal fats, such as lard and butter,
are saturated. They are solid at room
temperature.
An unsaturated fat, contains less than
the maximum number of hydrogen
atoms in one or more of its fatty acid
chains because some of its carbon
atoms are double-bonded to each
other.
The fats in fruits, vegetables, and fish
are generally unsaturated, as are corn
oil, olive oil, and other vegetable oils
Diets rich in saturated fats may be
unhealthy.
These diets may promote the buildup
of lipid-containing deposits, called
plaques, within the walls of blood
vessels.
Steroids
• A lipid molecule in which the carbon
skeleton forms four fused rings is
called a steroid.
• All steroids have a core set of four
rings, they differ in the kinds and
locations of functional groups attached
to the rings.
Steroids are classified as lipids because
they are hydrophobic, but they are very
different from fats in structure and
function.
Some steroids circulate in your body as
chemical signals.
The steroids estrogen, a female sex
hormone, and testosterone, a male sex
hormone, function in this way.
Cholesterol ( a steroid) is an essential
molecule found in the membranes
that surround your cells.
It is also the starting point from
which your body produces other
steroids.
Protein
• A protein is a polymer of just 20 kinds
of monomers called amino acids.
• Proteins are responsible for almost all
of the day-to-day functioning of
organisms.
Amino Acids
• Each amino acid monomer consists of
a central carbon atom bonded to four
partners.
• Three of the central carbon's partners
are the same in all amino acids.
• One partner is a hydrogen atom. Two
others are a carboxyl group and an
amino group, functional groups.
What is different about each type of
amino acid is the "side group" that
attaches to the fourth bond of the
central carbon.
The side group, sometimes called the
"R-group," is responsible for the
particular chemical properties of each
amino acid.
Building a Protein
• Cells create proteins by linking amino
acids together into a chain called a
polypeptide.
• Each link is created by a dehydration
reaction between the amino group of
one amino acid and the carboxyl group
of the next amino acid in the chain.
• Proteins are composed of one or more
polypeptide chains
Activation Energy
• To start a chemical reaction, it is
first necessary to weaken chemical
bonds in the reactant molecules.
• This "start-up" energy is called
activation energy because it
activates the reactants and triggers
a chemical reaction
Cellular reactions depend on the
assistance of catalysts, compounds
that speed up chemical reactions.
The main catalysts of chemical
reactions in organisms are
specialized proteins called
enzymes.
Enzymes provide a way for reactions
to occur at the cell's normal
temperature.
An enzyme doesn't supply activation
energy to the reacting molecules, but
instead lowers the energy
requirement.
Each enzyme catalyzes a specific
kind of chemical reaction.
At any moment in the cell's life, the
specific enzymes that are present
and active determine which
reactions occur.
How Enzymes Work
• The shape of each enzyme fits the shape
of only particular reactant molecules.
• A specific reactant acted upon by an
enzyme is called the enzyme's
substrate.
• The substrate fits into a particular region
of the enzyme, called the active site.
As with any other protein, an enzyme's
structure and shape are essential to its
function.
Factors such as pH and temperature can
greatly affect how well an enzyme works or if
it can work at all.
This is one reason why cells (and hence
organisms) can only survive and function
within certain ranges of conditions.