Compounds of Life
Biological Molecules
By
Joseph A. Castellano, Ph.D.
RESEED Silicon Valley
Reference: Focus on Physical Science, Glencoe/McGraw-Hill,
Columbus, Ohio, 2007, Pages 438-442. This textbook is used in
many California Middle Schools.
Biological Molecules
 Biological molecules present in all living
organisms include lipids (fats and oils),
proteins, nucleic acids and carbohydrates.
 Proteins, nucleic acids and carbohydrates are
large natural polymer molecules in all living
organisms that share the same few monomers:
- Amino acids make proteins
- Nucleotides make nucleic acids (DNA)
- Sugars make complex carbohydrates
Nucleic Acids
 A nucleic acid is a biomolecule found in all
plant, animal and human cells.
 RNA (ribonucleic acid) and DNA
(deoxyribonucleic acid) store cellular
information in all living cells in the form of a
“genetic code.”
 Every person’s genetic code is different. The
code in your cells determine the color of your
eyes and hair as well as every other feature of
your body that is unique to you and only you.
Nucleotide Monomers
 The nucleic acid DNA is composed of
monomers called nucleotides.
 A nucleotide is composed of a nitrogen base, a
sugar and a phosphate group:
Cytosine
(a nitrogen base)
Nucleotide Monomer
Nucleic Acid Polymers
 The nucleic acid polymer, DNA, is composed
of nucleotides that have the same four nitrogen
bases:
- Adenine
- Guanine - Cytosine
- Thymine
 Scientists identify these four by the first letter
of their names: A, G, C, T.
 A single DNA molecule can have thousands of
these nucleotides arranged in any number
of sequences (ATGCTGCA, etc.); the exact
sequence is the genetic code and is different for
each person.
DNA Chemical Structure
The dotted lines show
hydrogen bonds, which
hold the two strands of
Methane
nucleic acids together
in a coil-like
arrangement
called a “double helix.”
DNA Molecular Model
Methane
Lipids
 Lipids are fats and oils that contain carbon,
hydrogen and oxygen atoms.
 Like hydrocarbons, lipids are non-polar
compounds that are not soluble in water.
 Some lipids are long carbon chain, carboxylic
acids often called fatty acids.
 Neutral lipids in animal fats are fatty acids
combined with glycerol to form compounds
called fatty esters.
Lipids – Fats and Oils
 Fatty acid lipids can be saturated molecules with only
single bonds between carbon atoms. Bacon contains the
solid saturated fatty acid, stearic acid.
 Fatty acids with one or more double bonds between
carbons are called unsaturated and are usually liquid.
Olive oil contains the unsaturated lipid, oleic acid.
Carbohydrates
 A carbohydrate is an organic compound that
contains the elements carbon, hydrogen, and
oxygen. Carbo- stands for carbon and hydrate
for water.
 Simple Carbohydrates are sugars. There are
many different kinds of sugars. Some can
bought in boxes from the grocery store, but
many are also present naturally in foods such
as fruits and milk.
 Carbohydrates are used by cells to store and
release energy.
Simple Carbohydrates
 The simplest carbohydrate is glucose. The
molecular formula is:
C6H12O6
 The structural formula for glucose shows how
the atoms are arranged.
Carbohydrates with only one carbon
ring are called monosaccharides
Complex Carbohydrates
 A complex carbohydrate is a long chain polymer
made up of simple carbohydrate monomers.
 Starch, cellulose and glycogen are all built from
glucose monomers, but the monomers are
arranged differently in each case.
 Starch and cellulose are found in plants, while
glycogen is present in liver and muscle cells.
Complex carbohydrates have many carbon rings,
so they are called polysaccharides.
Polymers from Glucose
Plants, Trees,
Fruits, Vegetables
Straight Polymer Chain Backbone
Cellulose
Glucose
Animal & Human
Liver & Muscles
Branched Polymer Chain Backbone
Glycogen
Proteins
 Proteins are long chain polymer molecules
formed by connecting amino acids together.
 Glycine is the simplest of the 20 common amino
acids that occur in nature.
Proteins
 Proteins are made in human cells by a complex
process involving DNA.
 The DNA directs the amino acids to combine
with each other in a very specific sequence to
produce the desired protein for each organ.
 For example, the protein collagen makes up
skin while hemoglobin is the protein in blood
that carries oxygen to our cells.
 Other proteins contract muscle tissue and fight
viruses and bacteria that invade us.
Protein Structure
 Proteins in nature have a
helical structure, like a coil.
 The dashed lines in this
protein molecular model
represent “hydrogen bonds”
that hold the atoms in the
coil-like structure.
Summary
 All living organisms are composed of biological
molecules that contain carbon, hydrogen, oxygen,
nitrogen and sometimes sulfur and phosphorous.
 Nucleic acids, proteins, lipids and carbohydrates
are the main compounds of life.
 Biological molecules are formed from amino
acids, sugars, long chain “fatty acids” and
nucleotides.
 Research on biological molecules leads to an
understanding of the causes and cure of human
diseases.
This presentation was produced as a public service
to help middle school and high school science
teachers develop experiments, presentations and
demonstrations that can be used in their classes.
More science experiments and demonstrations are
available on the RESEED Silicon Valley web site:
www.reseed-sv.org.
RESEED (Retirees Enhancing Science Education
through Experiments and Demonstrations) is a
program aimed at stimulating greater interest in
science by middle school students.