Chapter 3
The Molecules of Cells
By Dr. Par Mohammadian
Overview:
-Carbon atom
-Functional Groups
-Major Biomolecules
Life’s molecular diversity is based on
the properties of carbon
– Cell consists mostly of carbon-based
molecules
– Organic chemistry: Study of carbon
compounds
Carbon:
– It has four electrons in an outer shell that holds
eight
– Carbon can share its electrons with other atoms
to form up to four covalent bonds
• The simplest organic compounds are
hydrocarbons
– These are organic molecules containing only carbon
and hydrogen atoms
– The simplest hydrocarbon is methane
Functional groups help determine the
properties of organic compounds
• The unique properties of an organic compound
depend not only on its carbon skeleton but also
on the atoms attached to the skeleton
– These atoms are called functional groups
• Functional groups are the groups of atoms that
participate in chemical reactions
– Hydroxyl groups are characteristic of alcohols
– The carboxyl group acts as an acid
Cells make a huge number of large
molecules from a small set of small
molecules
• Most of the large molecules in living things
are macromolecules called polymers (e.g.
proteins, DNA)
– Polymers are long chains of smaller molecular
units called monomers
– A huge number of different polymers can be
made from a small number of monomers
• Cells link monomers to form polymers by
dehydration synthesis
• Polymers are broken down to monomers by the
reverse process, hydrolysis
BIOLOGICAL MOLECULES
• There are four categories of large molecules
in cells
– Carbohydrates
– Lipids
– Proteins
– Nucleic acids
Carbohydrates
• Carbohydrates include
– Small sugar molecules in soft drinks
– Long starch molecules in pasta and potatoes
Monosaccharides are the simplest carbohydrates
• Monosaccharides
• The
are simple sugars
monosaccharides
glucose and
– Their atoms are
fructose are
arranged
differently
isomers
Disaccharides
• A disaccharide is a double sugar
• Disaccharides are joined by the process of dehydration synthesis
– It is constructed from two monosaccharides
• The most common disaccharide is sucrose,
common table sugar
– It consists of a glucose linked to a fructose
– Sucrose is extracted from sugar cane and the roots of
sugar beets
• Simple sugars and double sugars dissolve readily
in water
– They are hydrophilic
Polysaccharides
• Complex carbohydrates are called
polysaccharides
– They are long chains of sugar units
– They are polymers of monosaccharides
• These large molecules are polymers of hundreds
or thousands of monosaccharides linked by
dehydration synthesis
• Starch and glycogen are polysaccharides that
store sugar for later use
• Cellulose is a polysaccharide in plant cell walls
Lipids
• Lipids are hydrophobic
– They do not mix with water
– Examples: fats and steroids
• Fats are lipids whose main function is energy
storage
– They are also called triglycerides
• A triglyceride molecule consists of one glycerol
molecule linked to three fatty acids
• The fatty acids of unsaturated fats (plant oils)
contain double bonds
– These prevent them from solidifying at room
temperature
• Saturated fats (lard) lack double bonds
– They are solid at room temperature
Phospholipids, waxes, and steroids are lipids with a
variety of functions
• Phospholipids are a major component of cell
membranes
• Waxes form waterproof coatings
• Steroids
are often
hormones
Steroids
• Steroids are very different from fats in structure
and function
– The carbon skeleton is
bent to form four fused
rings
• Cholesterol: your
body produces other
steroids
PROTEINS
Proteins are essential to the structures and activities of life
• Proteins are involved in
–
–
–
–
–
cellular structure
movement
defense
transport
communication
• Mammalian hair is composed of structural
proteins
• Enzymes regulate chemical reactions
The Monomers: Amino Acids
• Each amino acid
consists of
– A central carbon
atom bonded to
four covalent
partners
– an amino group
– a carboxyl group
– A side group that
is variable among
all 20
• All proteins are
constructed from
a common set of
20 kinds of amino
acids
Proteins as Polymers
• Cells link amino
acids together by
dehydration
synthesis
– The resulting
bond between
them is called a
peptide bond
• Your body has tens of
thousands of different
kinds of protein
– The arrangement of
amino acids makes each
one different
Overview: A protein’s specific shape determines its
function
• A protein, such as lysozyme, consists of
polypeptide chains folded into a unique shape
– The shape determines the protein’s function
– A protein loses its specific function when its
polypeptides unravel
A protein’s primary structure is its amino acid
sequence
Secondary structure is polypeptide coiling or folding
produced by hydrogen bonding
Tertiary structure is the overall shape of a
polypeptide
Quaternary structure is the relationship among
multiple polypeptides of a protein
What Determines Protein Structure?
• A protein’s shape is sensitive to the surrounding
environment
– Unfavorable temperature and pH changes can cause a
protein to unravel and lose its shape
– This is called denaturation
NUCLEIC ACIDS
Nucleic acids are information-rich polymers of nucleotides
• Nucleic acids such as deoxyribonucleic acid
(DNA) and ribonucleic acid (RNA) serve as the
blueprints for proteins
• They ultimately control the life of a cell
• Nucleic acids are polymers of nucleotides
– Each nucleotide is composed of a sugar, phosphate,
and nitrogenous base (RNA has A, C, G and instead of
T, it has uracil (U).
• Each DNA
nucleotide has
one of the
following bases
–
–
–
–
Adenine (A)
Guanine (G)
Thymine (T)
Cytosine (C)