Before DNA Was Established as the Genetic Material, Proteins Were

Multiple Choice

Before DNA was established as the genetic material, proteins were considered the most likely molecules to serve this role. In part this belief was based on the fact that there are 20 building blocks (20 different kinds of amino acids) for proteins versus 4 building blocks (4 different nucleotides) for DNA. If proteins stored a code, there would be a far greater number of code words possible for a protein of a given number of amino acids than for a DNA molecule of the same number of nucleotides. For example, there are 16 different sequences (4²) possible for a DNA two nucleotides long and 400 (20²) different sequences possible for a protein two amino acids long. For a sequence three nucleotides or three amino acids in length, the number of distinct DNA sequences is ________, and the number of distinct protein sequences is ________.

A) 64; 8,000
B) 800; 8,000
C) 30; 800
D) 64; 800
E) 20; 420