Structure and Function of Macromolecules
from Campbell's Biology, Benjamin/Cummings
Publishing Co., 1990. Further adapted from
- Cells can combine small organic molecules into large
macromolecules, forming a higher level in the biological hierarchy of
- Carbohydrates, lipids, proteins, and nucleic acid are
the four major classes of organic
compounds in cells.
chains of identical or similar subunit molecules called monomers.
Although there is a limited number of monomers common to all organisms each
organism is unique because of the specific arrangement of these monomers into
polymers with distinctive structures and properties.
- Monomers of all four classes of macromolecules form
larger molecules by dehydration
synthesis, a chemical reaction in which one monomer donates a hydroxyl
group and the other a hydrogen atom, forming a water molecule
- Polymers can be disassembled to monomers by the
reverse process, called hydrolysis.
In this way, large macromolecules in food are digested into monomers small
enough to enter our cells.
- Carbohydrates are sugars and their derivatives.
are the simplest carbohydrates, used directly for fuel, converted to the other
types of organic molecules, or used as a monomer units for carbohydrate
- All monosaccharides possess a carbon skeleton of three
to seven carbons, all but one of which are bonded to a hydroxyl group.
- In aqueous solution (dissolved in water), most monosaccharides form
consist of two monosaccharides monomers connected by a covalent
bond. The monosaccharides can be the same or different.
may consist of thousands of monosaccharide monomers connected by glycosidic
in plants and glycogen
in animals are both storage polymers of glucose. Cellulose
is an important structural polysaccharide in the cell
walls of plants.
- Lipids make up the most structurally heterogeneous
class of macromolecules, but all share the the property of being wholly or
- Fats are high energy, compact storage molecules also
known as triacylglycerols
or triglycerides. They are constructed by joining a glycerol molecule to
- Fatty acids consist of a carboxyl group and a hydrophobic
fatty acids have the maximum number of hydrogen atoms because of single
bonding between all the carbons. Unsaturated
fatty acids (present in oils) have one or more double bonds between the
carbons, causing kinks in the molecule and reducing the number of bonding
sights for hydrogen atoms.
substitute the third fatty acid of a triacylglycerols with a negatively
charged phosphate group, which may be joined, in turn, to another small
molecule. Such bonding introduces polarity
and hence water solubility
to one end of the molecule, making phospholipids ideally suited for
construction of cell
- Proteins are polymers constructed from 20 different amino
acids. They are the most complex and versatile macromolecules, with
emergent properties arising from their intricate architecture.
- An amino acid is composed of a central asymmetrical
carbon singly bonded to a hydrogen atom, a carboxyl group, an amino
group, and a variable side chain that confers unique properties on each
- The carboxyl and amino groups of adjacent amino acids
link together in a peptide
bond, forming long polymers.
- Protein conformation can be described by three or four
superimposed, hierarchical levels. Primary structure is the first level and
describes the unique sequence of amino acids.
- Secondary structure describes how the primary is
folded into particular shape.
- The function of a protein is
dependant upon it's shape, which is highly sensitive to conditions such as pH, salt
concentration, and temperature. Changing these conditions can cause the
protein to denature
by altering its shape in such ways that it no longer has a biological
- Protein shape is ultimately determined by its primary
structure. Molecular biologists are looking for rules that will predict
protein folding and final conformation from an amino acid sequence.
- Nucleic acids are polymers consisting of nucleotides,
complex monomers consisting of a pentose (five-carbon sugar) covalently
bonded to a phosphate
group and to one of five different kinds of nitrogenous
- DNA is a helical,
double-stranded polymer with bases A, G, C, and T projecting into the
interior of the molecule. A always hydrogen bonds to T, and C to G. Thus, the
nucleotide sequence of the two strands is complementary,
and one strand can serve as a template
for the formation of the other.
- The property of complementary strands give DNA its
unique ability to replicate
itself and provides a mechanism for the continuity of life. Once replicated
specific nucleotide segments of the DNA (genes)
program the manufacture of an organism's characteristic proteins. RNA
functions in protein