Datasheet

After the nucleotides are linked, the resulting DNA strand exhibits an unused
phosphoryl group (PO
4
) at the 5' end, and an unused hydroxyl group (OH) at
the 3' end. These extremities are respectively called the
5'-terminus and the
3'-terminus of the DNA strand.
A DNA sequence is always defined (in books, databases, articles, and pro-
grams) as the succession of its constituent nucleotides
listed from the 5'- to
3
'- terminus (that is, end). The sequence of the (short!) DNA strand shown in
Figure 1-5 is then
TGACT = Thymine-Guanine-Adenine-Cytosine-Thymine
The two sides of a DNA sequence
In the same laboratory where Kendrew and Perutz were trying to figure out
the first 3-D structure of a protein, Watson and Crick elucidated — in 1953 —
the famous double-helical structure of the DNA molecule. These days every-
body has a mental picture of this famous spiral-staircase molecule; the ele-
gance of the DNA
double helix probably helped make it the most popular
notion to come out of molecular biology. But what made this discovery so
important — earning one more Nobel Prize for molecular biology — was not
the helical shape, but the discovery that the DNA molecule consists of two
complementary strands, shown in Figure 1-6.
T G A C
5' P3'- 5' 3'- 5' 3'- 5' 3'- 5' 3' OH
T
Figure 1-5:
Chained
nucleotides
constituting
a DNA
strand.
5' P3' OH
T GA C
5' P3' OH 5' P3' OH 5' P3' OH
Figure 1-4:
The four
nucleotides
making
DNA.
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Part I: Getting Started in Bioinformatics
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