A. DNA, RNA, and protein
Molecules of inheritance
In the early 1900s, DNA was shown to consist of building blocks called nucleotides (see Figure 2.2 in Chapter 2). At the time, DNA was not considered the likely molecule of inheritance. Protein, the other known component of chromosomes, was the favored molecule. It was known that proteins consisted of amino acids; at least 20 had been discovered, whereas DNA had only 4 different nucleotides. In view of its more complex structure, protein was thought to be more capable of storing the vast amounts of information needed for millions of inherited traits than the simpler DNA structure with just four different nucleotides.
However, the protein model of inheritance had fallen into doubt by 1944, following ...