One of the most important
activities of a cell is the production of
proteins that fulfill major roles in the cell--structural, enzymatic,
hormonal, and more.
The instructions for building all the
proteins an organism needs to make are located in the DNA molecules of the
chromosomes which never leave the nucleus of the cell. However, the actual synthesis is carried out by the
small structures which either float freely in the cytoplasm or are
attached to membrane networks that snake their way through the cell--in
either case, outside the nucleus.
This section will explain briefly and superficially the way the
instructions reach the ribosomes and how they are translated into the
language of proteins. This information is not critical for
understanding the use of DNA for genealogy but does form a foundation for
understanding the way genetic mutations are expressed and a basis for
understanding genetic differences.
is a chainlike molecule built of subunits of smaller molecules called amino acids. We obtain most of
our amino acids by digesting proteins taken in with our food. The
digestive process breaks the protein chains down into individual amino
acid molecules which are then absorbed by the blood and transported to the
individual body cells.
the separate amino acids are reassembled into new chains.
kind of protein has its own particular sequence of amino acids, which differs from
the sequence in every other kind of protein. Just the way the order
of letters in a word give it its own specific form and meaning, it is the
order of the amino acids in the chain that determines the protein's
structure and function.
The code for
ordering the amino acids of a protein is written as a sequence of
bases in the DNA in the nucleus.
However, since DNA
never leaves the nucleus and proteins are constructed by ribosomes in the
cytoplasm of the cell, the instructions must somehow be
carried out of the nucleus to the ribosomes.
This is accomplished
when the double spiral of DNA unwinds and unzips a little at the point
where the instructions for the given protein are located.
(This section of the DNA molecule is called
While it is unzipped, this short section of the DNA
acts as a pattern or
template for another kind of nucleicacid called RNA (ribonucleic acid)
Each adenine of the unzipped DNA attracts a uracil, U, (instead of a
thymine as in DNA). The other bases, G, T, and C attract the same
partners as they do in DNA replication, G attracts C, C attracts G, and T