Putting DNA to Work
  DNA SEQUENCE

Unzipping DNA

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The Sequence On One Strand

The DNA molecule is composed of two very long strands of A’s, T’s, G’s and C’s, which are tightly paired with each other. An A on one strand is always paired with a T on the other strand, and a G is always paired with a C. This means that if the sequence of nucleotides on one strand is known, the sequence of the other strand will be automatically known as well.

One strand of DNA is like a photographic negative of the other strand. A negative can be used to make many copies of a photograph because it contains all of the information that is part of that photograph. Similarly, to read the sequence of A’s, T’s, G’s, and C’s in a genome, it is only necessary to read one strand of DNA to be able to deduce the sequence of the other strand.

Graphic of DNA base pairing 

One Strand of DNA Is Like a Photographic Negative to the Other

An adenine (A) on one strand is always paired with a thymine (T) on the other strand, and a guanine (G) is always paired with a cytosine (C). If the sequence of nucleotides on one strand is known, the sequence of the other strand will be automatically known as well.


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