Biomedical Engineering Reference
In-Depth Information
when a modified base is added. At the end of the process, each tube
(the A, T, C, and G tubes) will contain a mixture of many copies
of different-sized products, the length of each determined by the
location of that base. Each reaction mixture is injected into a tube
filled with a plastic-like material that separates the DNA pieces
by size. The size of the fragments flowing out of the four tubes is
“read” by a machine that picks up the dye molecule of the primer.
Computer programs interpret the results and generate the sequence
by analyzing which base is added, as the products of the four tubes
get longer, base by base.
Stop and Consider
Moving genes from one species to another is distasteful to some
people because it allows genetic changes to occur outside the
natural mating processes. What are your opinions on this issue?
Would they be influenced by the planned use of a particular
biotechnology product?
From Gene to Protein
Genes are composed of the sequence of As, Ts, Cs, and Gs that the
cell decodes to make up a protein. The code for each of the 20 amino
acids is a particular triplet of bases. When a cell manufactures a
protein, intermediate copies of the gene sequence are made, in the
form of
messenger ribonucleic acid
(
mRNA
), and these copies move
to the
ribosomes
, the protein-manufacturing structures of the cell.
In the ribosome, the code is read from the triplets of RNA bases
that specify the amino acids. RNA is composed of four bases that
are slightly different chemically from the bases of DNA. The sugar
portions of the DNA bases have one less oxygen atom than the RNA
bases do. Amino acids are shuttled to the ribosome and lined up by
another type of RNA called
transfer RNA
(
tRNA
). For each amino
acid, a specific tRNA, carrying the base sequence that complements
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