Video Transcript
A strand of DNA has the sequence
five prime ATATGCGC three prime. State the corresponding sequence on
the complementary strand, reading from the three prime to five prime direction. (A) ATATGCGC, (B) TATACGCG, or (C)
CACATGTG.
DNA is a double-stranded polymer,
made up of many repeating units known as nucleotides. Each nucleotide is composed of a
phosphate group, a sugar, and a nitrogenous base. DNA has four bases: adenine,
thymine, cytosine, and guanine. Each of these bases is the
complement to another. Adenine complements thymine, and
cytosine complements guanine. The two strands of DNA are held
together by the hydrogen bonds between the complementary bases.
Another important feature of DNA is
that each strand has a direction. Because of the asymmetrical shape
of nucleotides and the way that the sugar phosphate backbone forms, one end of a
single strand of DNA is different from the opposite end. The end that terminates in a
phosphate group is known as the five prime end, and the end that terminates in a
hydroxyl group is known as the three prime end.
The complementary strand of DNA
runs in the opposite direction. This directionality is extremely
important for cellular machinery to be able to translate the genes into
proteins.
So now that we understand how a
piece of DNA is composed, we can figure out the complementary sequence to this piece
of DNA. Remember that the complement to
adenine, or A, is thymine, or T. And likewise, the complement to T
is A. Also, remember that the complement
to guanine, or G, is cytosine, or C, and vice versa. So the correct sequence for the
complementary strand running in the three prime to five prime direction is (B)
TATACGCG.
