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This lecture is about
Watson-Crick Model of DNA
In 1953, James Watson and Francis Crick proposed the structure for DNA.
According to the Watson-Crick model, a DNA molecule consists of two polynucleotide strands.
These strands are coiled around each other in the form of a double helix. There is a phosphatesugar backbone on the outside of double helix, and the nitrogenous bases are on the inside. In
double helix, the nitrogenous bases of opposite nucleotides form pairs through hydrogen bonds.
This pairing is very specific. The nitrogenous base adenine of one nucleotide forms pair with the
thymine of opposing nucleotide, while cytosine forms pair with guanine. There are two hydrogen
bonds between adenine and thymine while there are three hydrogen bonds between cytosine
and guanine.
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