Honors Biology
The molecules of Cells
Chapter 3
Life’s molecular diversity
is based on the properties
of carbon
 Most compounds in living organisms are
organic – composed of carbon bonded to
other elements. Functions of organic
compounds:
 Main structural components of cells and
tissues
 Participate in and regulate many chemical
reactions
 Provide energy
 By sharing electrons, carbon can bond to
four other atoms.
 This allows for branching in up to four
directions.
 A chain of carbon atoms is called a
carbon skeleton.
 Carbon skeletons can be branched or
unbranched.
 Therefore, different compounds with the
same molecular formula but different
properties can be produced.
 These structures are called ISOMERS.
 Carbon skeletons can vary in:



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Length
Branching
Double bonds
Rings
 An organic compound has unique
properties that depend upon:
 The size and shape of the molecule and
 The groups of atoms (functional groups)
attached to it.
 A functional group affects a biological molecule’s
function in a characteristic way.
 Compounds that contain functional groups are
hydrophilic (water-loving)
Cells make a huge number of large
molecules from a small set of small
molecules
Four classes of biological molecules:
Carbohydrates
Lipids
Proteins
Nucleic Acids
 The four classes of biological molecules
contain very large molecules
 They are often called macromolecules
because of their large size
 They may also be called polymers when
they are made from identical building blocks
strung together
 The building blocks of polymers are called
monomers.
 Dehydration synthesis (condensation) is
the linking of monomers by the removal
of water. This reaction builds polymers.
 Hydrolysis (“to break, with water”) breaks
down polymers to monomers by adding
water.
 A good example of hydrolysis is when
you digest your food!
Carbohydrates
 Serve as fuel and structural components
for cells
 General structure: contain carbon,
hydrogen and oxygen in a ratio of about
1:2:1
Classification of
Carbohydrates
 Monosaccharides: contain one type of
sugar unit
 Disaccharides: contain two types of
sugar units
 Polysaccharides: contain many sugar
units
Monosaccharides
 Also known as simple sugars
 Example: glucose is an important fuel
molecule in living cells
 Monosaccharides are also used as raw
materials to manufacture other organic
molecules
 Monosaccharides are the monomers for
disaccharides and polysaccharides.
Polysaccharides
 Composed of repeating monosaccharide
units
 They can function in the cell as a storage
molecule or as a structural compound
Storage Polysaccharides
 Starch – storage polysaccharide of plants
 Glycogen – storage polysaccharide of
animals
Structural
Polysaccharides
 Cellulose is a polymer of glucose that
forms plant cell walls.
 Chitin is a polysaccharide that is a
structural component of the exoskeleton
of insects and crustaceans. (also used in
surgical thread for stitches that dissolve!)
Lipids (fats)
 Lipids are water insoluble (hydrophobic –
“water fearing”) compounds that are
made from glycerol and fatty acids.
 They contain twice as much energy as a
polysaccharide, so their main function is
long-term energy storage.
 Lipids differ from other organic
compounds in that they are neither huge
macromolecules nor polymers.
 Three types of lipids:
 Fat
 Phospholipids
 Steroids
Types of Fats:
 Unsaturated – corn oil, olive oil, and other
vegetable oils. Liquid at room temperature.
 Saturated – have the maximum number of
hydrogens. Examples include beef fat and
butter. Solid at room temperature.
 Trans fat – made by adding hydrogen to
unsaturated fats. Associated with health
risks.
 Phospholipids – a modified fat that is the
main structural component of cell
membranes.
 Steroids – cholesterol is a common
component of cell membranes. Animal
cells use it as a precursor for making
other steroids, including hormones.
Proteins
 A protein is a polymer built from various
combinations of 20 amino acid
monomers.
Proteins are essential to the
structures and functions of life
 Structural proteins provide associations
between body parts.
 Contractile proteins are found within
muscle.
 Defensive proteins include antibodies of
the immune system.
 Signal proteins are best exemplified by
the hormones
 Receptor proteins serve as ‘antenna’ for
outside signals
 Transport proteins carry oxygen.
 Enzymes regulate the chemical
reactions within cells.
Proteins are made from amino
acids linked by peptide bonds
 This is done by means of an enzymemediated dehydration synthesis.
 A polypeptide chain contains hundreds or
thousands of amino acids.
 The amino acid sequence causes the
polypeptide to assume a particular shape
 The shape of a protein determines its
specific function.
Levels of protein
organization
 Primary structure – unique sequence of
amino acids
 Correct amino acid sequence is determined
by the cell’s genetic information
 The slightest change in this sequence
affects the protein’s ability to function.
 Secondary structure – coiling or folding
of the peptide chain
 Coiling results in a helical structure called an
alpha helix
 Folding may lead to a structure called a beta
pleated sheet.
 Tertiary structure – overall 3-D shape
 Quaternary structure – how the
polypeptides fit together in a molecule
Protein structure
determines function
 Changes in protein structure can affect
function
 Mutations can disrupt the biological
activity of a protein
 Denaturation can cause the protein to
become inactive
Nucleic acids are informationrich polymers
 Two classes – RNA and DNA
 Nucleic acids store information that
codes for proteins, which govern the
structure and function of the organism
Composition of nucleic
acids
 Monomers are nucleotides
 Each nucleotide is composed of:
 Nitrogenous base
 5-carbon sugar
 Phosphate group