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The living cell is a symphony of thousands of
chemical reactions all miraculously timed and coordinated to
perform all the functions necessary for life.
Amazingly, this symphony has only a few major players; only six elements
carbon,
hydrogen, oxygen, nitrogen, phosphorus, and sulfur
(sometimes called CHNOPS;>) make up about 98% of the mass of all living
organisms.
Carbon
is a unique
element with the remarkable ability to form strong, stable
chemical bonds with other atoms (keeps you from
falling apart.) Each
carbon atom can form four bonds with other atoms.
(Sometimes, two atoms will form more than one bond between themselves
making a double bond or even a triple bond.)
This bonding ability allows carbon atoms to form chains of almost
unlimited length. These chains can be closed on themselves to form rings
or may branch wildly. This gives great variety to the kinds of molecules
that carbon can form. Below are just a few examples of the many ways
carbon chains can be arranged to form the skeleton for different
molecules.
Atoms
of hydrogen and oxygen and less frequently nitrogen, sulfur, or
phosphorous are bonded to the carbon skeleton to form giant molecules
called macromolecules. A few other elements may occur in trace amounts.
The four major types of macromolecules found in living
cells—carbohydrates, lipids, proteins, and nucleic acids--are made of
smaller, repeating subunits called monomers. The monomers are not always
identical but they always have similar chemical structures. They are
joined together by a series of chemical reactions in a process called
polymerization to form large, complex molecules called polymers.
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The Four Major
Types of Macromolecules Found in Living Cells |
|
Macromolecule |
Elements |
Monomer
|
Polymer |
example |
|
Carbohydrate |
C, H, O |
Simple sugars |
Polysaccharide |
Starch |
|
Lipids |
C, H, O |
Fatty acids & glycerol |
Lipid |
Fats, oils, waxes |
|
Proteins |
C, H, O, N, S |
Amino acids |
Polypeptides |
Insulin |
|
Nucleic acids |
C, H, O, P |
Nucleotides |
Nucleic
acids |
DNA |
The chemical diversity
that polymerization allows living things is similar to the diversity that
our alphabet allows our language. Although there are only 26 letters in
our English alphabet, our ability to join them together to form
words gives us an almost infinite variety of possible words. Similarly,
the monomer units of macromolecules can be arranged with an almost endless
potential for variety.
The
functions of macromolecules are directly related to their shapes and to
the chemical properties of their monomers. The way the monomers are
arranged in the macromolecule determines its shape and its function in the
same way that the arrangement of the letters in a word determine its sound
and meaning.
Much of a cell's activities involve the arranging and rearranging and
bonding of macromolecules. It is the job of DNA both directly and
indirectly to coordinate and direct these activities.
An understanding of the structure and functions of carbohydrates and
lipids is not particularly key to the understanding of molecular
genealogy. However, it may be helpful to take a quick look at the
structure and function of proteins before moving on to the nitty gritty of
the nucleic acids (of which DNA is one.)
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