The genetic material performs four important functions, and the DNA structure proposed by Watson and Crick was elegantly suited to three of them.
The genetic material stores an organism’s genetic information. With its millions of nucleotides, the base sequence of a DNA molecule can encode and store an enormous amount of information. Variations in DNA sequences can account for species and individual differences. DNA fits this role nicely.
The genetic material is susceptible to mutations (permanent changes) in the information it encodes. For DNA, mutations might be simple changes in the linear sequence of base pairs.
The genetic material is precisely replicated in the cell division cycle. Replication could be accomplished by complementary base pairing, A with T and G with C. In the original publication of their findings in 1953, Watson and Crick coyly pointed out, “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.”
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The genetic material (the coded information in DNA) is expressed as the phenotype. This function is not obvious in the structure of DNA. However, as we will see in the next chapter, the nucleotide sequence of DNA is copied into RNA, which uses the coded information to specify a linear sequence of amino acids—