Complementarity of DNA Strands

One of the biggest breakthroughs in Biology came when scientists named James Watson and Francis Crick proposed their model for the structure of DNA.  One of the sentences at the end of their historic one-page article is particularly important:

“It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.”

In this one sentence, they proposed that because nucleotides on opposite DNA strands always paired in a very specific way – A with T, and C with G – it was possible for a single strand to act as a template for the formation of the opposite strand.

This property of complementarity was later used by scientists to develop tools that would help them find specific DNA sequences (ie. -ATGCGTGTCGAGGCTCG- ) by using a single strand of nucleotides with a complementary sequence (a probe) that could specifically bind to it:

Synthetic Probe ->       -TACGCACAGCTCCGAGC-
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Target DNA Sequence ->   -ATGCGTGTCGAGGCTCG-

Comprehension Question

If you can generate a single-stranded molecule with a specific sequence, it could potentially be used to find and bind to a complementary sequence on the DNA molecule.

Correct

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Incorrect

Please go here to learn more about base-pairing in DNA.