The Four Major Groups of Organic Compounds:
Carbohydrates, Lipids, Proteins, and Nucleic
Acids; and Their Functions in Living Systems
Carbon
a Most Versatile Atom
-The Carbon atom has
•6 protons
•6 neutrons
•6 electrons
-Carbon has 4 electrons in its
outermost energy level, therefore it
needs four electrons to complete
its octet.
-Carbon covalently shares
electrons with up to four other
atoms. This characteristic makes
Carbon very versatile when it
comes to chemical structures.
│
—C—
│
Carbon’s Chemical Properties and Molecular Diversity
Carbon Skeletons Vary
• Carbon chains
– Vary in length
– May be linear or branched
– May contain only c-c single
bonds or may contain
double and/or triple bonds
at various locations
• Carbon rings
– May contain only single c-c
bonds, or may contain
double bonds
Functional Groups Confer Specific
Properties to Carbon Compounds
• Carbon skeletons come
in may shapes and
forms. These are
basically Hydrocarbons
(molecules composed of
only Carbon and
Hydrogen atoms).
• Functional groups, have
specific properties
characteristic to their
chemical structure and
further add variety to the
Hydrocarbon skeleton
molecular structures.
Functional Groups and Their Functions
Hydroxyl Group
— OH
Alcohols
Carbonyl Group
—C=O
│
Aldehydes
Ketones
Carboxyl Group
— COOH
Organic Acids
Carboxylic Acid
Amino Group
— NH2
Organic Bases
Amines
Phosphate
Group
— OPO32-
Organic
Phosphates
Monomers ↔ Polymers
Dehydration ↔ Hydrolysis
• Monomers are
molecules that are
chemically bonded
through dehydration
synthesis to make
polymers, which are
the functional
macromolecules.
• Polymers can be
broken down into their
monomer components
through hydrolysis.
Carbohydrates aka Saccharides Are Aldoses
and Ketoses
• Carbohydrates have the atomic
ratio C:H2O.
• They are composed of many
monosaccharide (monomers)
chemically combined through
dehydration synthesis into
polysaccharides (polymers).
• Glucose C6H12O6 is made by
plants and is the most common
monosaccharide.
• Serve as energy sources for
plants, animals and other
organisms. Converted into ATP
energy.
• Serve as structural molecules in
plants and other organisms.
• Dietary source: plant products.
• Cellulose is bulk or fiber.
Polysaccharides
Cellulose
Most abundant glucose
polymer, component
of plant cell walls
Starch
Plants store glucose in
starch polymers
(grains, tubers). Serve
as glucose source for
animals.
Glycogen
Very branched glucose
polymer. Animals store
glucose as glycogen.
AKA animal starch.
Lipids Are Hydrophobic
• Lipids include:
fatty acids, steroids,
phospholipids, and waxes.
Saturated Fats
from animal sources
Unsaturated Fats
from plant sources
• Because they are not soluble
in water, they are good
structural, insulation,
transport, and storage
macromolecules,
such as:
– Adipose tissue
– cell membranes
components
– hormones
– triglycerides
– oils and waxes
Fatty Acids Are Long Hydrocarbons with a Carboxylic
Acid Functional Group
• Saturated fatty acids usually come from animal sources and
are solid at room temperature, these are high in caloric
value.
• Unsaturated fatty acids usually come from plant sources
and are liquid at room temperature, these are lower in
caloric value.
Triglycerides: Three Fatty Acids Dehydrated to One Glycerol
-The diagram to the left,
depicts a glycerol being
dehydrated with a fatty
acid.
-This reaction occurs a
total of three times to
form a triglyceride, as
seen on the diagram to
the right
-Triglyceride molecules
transport fats in the
bloodstream and serve
as building blocks for
other lipids, such as
phospholipids.
Steroids
. A steroid’s structure is composed of carbon rings.
. Steroids serve as the structural components of many hormones, such as
estrogen and testosterone.
. Steroids are essential for maintaining the fluidity of cell membranes.
. Diets rich in saturated fats promote accumulation of LDL “bad
cholesterol” in the wall of arteries, reducing blood flow and promoting
hypertension and the incidence of strokes.
Proteins
• Proteins are the structural components of living tissue.
They also serve as enzymes, hormones, and
immunoglobulins, among many other roles.
• Proteins are composed of amino acids (a.a.). We
acquire a.a. by consuming meat, fowl, fish, dairy, eggs,
legumes, and nuts
Proteins: Composed of Amino Acids
• Amino acids are the
monomers that are
dehydrated to form
polypeptides or proteins.
• Humans have about 20
different amino acids from
which proteins are
synthesized. The difference
between one protein and
another has to do with the
number of amino acids that a
protein contains and the
unique sequences in which
the amino acids are arranged.
• Protein synthesis occurs in the
ribosomes of cells and is
controlled by genetic
information.
Amino Acids (a.a.)
Have both amino and carboxyl
functional groups. The “R” group
varies for each of the 20 a.a.
Protein Synthesis:
• Amino acids are chemically combined through
dehydration synthesis by peptide bonds to form
polypeptides (protein)
• The sequence of amino acids in a polypeptide is
determined by genetic information
A Protein Structure Determines Its Function
Primary structure
determined by a.a.
sequence
Secondary structure
determined by Hydrogen
bonding:
α helix or β sheet
Tertiary structure
polypeptide folding due
to covalent and ionic
bonds
Quaternary
structure
Two or more
polypeptides chemically
combined
Nucleic Acids Have Sugars, Nitrogenous Bases
and Organic Phosphate Components
• Nucleic Acids serve as
information
macromolecules, such
as DNA and RNA. (We
will study these further
in the future.)
• Another type of Nucleic
Acid, ATP, serves as
the energy currency of
cells. (We will study
ATP further in the
future.)
• Nucleotides (picture at
left) are the molecular
components of Nucleic
Acids.
DNA for Hereditary Information
Nucleotides are
chemically joined to
form DNA, a double
stranded helix. The
bases, of each strand,
hydrogen bond to each
other.
The phosphates and
sugars form the
backbone of the double
helix. The sequence of
bases on the DNA
determines the amino
acid sequence of
proteins.
Four types of bases:
Adenine (A), Guanine
(G), Thymine (T), and
Cytosine (C). These
bases bind to each
other. A always binds
with T,
G always binds with C.
Structure Is Always Related to Function
• Living organisms
require thousands
of different types
of molecules to
maintain their
structure and
sustain their
body’s functions.
• The ability of
Carbon to bond
with four other
atoms is the basis
for the vast variety
of chemical
structures found in
organisms.