Who proposed that the genetic code for amino acids should be made up of three nucleotides?

The correct option is George Gamow.

Step-by-Step Explanation:

1. Understanding the Problem: The genetic code consists of codons, which are sequences of nucleotides in DNA or RNA that determine the sequence of amino acids during protein synthesis. We need to identify the scientist who first proposed that each codon must be a triplet (composed of three nucleotides).

2. The Mathematical Logic:
There are only 4 different types of nucleotides (Adenine, Uracil/Thymine, Cytosine, Guanine) present in RNA/DNA, whereas there are 20 standard amino acids that need to be coded.
If the code were singlet (1 nucleotide per amino acid), it could code for only 4¹ = 4 amino acids.
If the code were doublet (2 nucleotides per amino acid), it could code for only 4² = 16 amino acids, which is still insufficient for 20 amino acids.
Therefore, a triplet code (3 nucleotides per amino acid) is the minimum required size, as it can generate 4³ = 64 possible codons, which is more than enough to code for all 20 amino acids.

3. Historical Context: This mathematical hypothesis was proposed by the physicist George Gamow in 1954, shortly after the discovery of the double-helical structure of DNA. His proposal of the triplet code was later experimentally proven by scientists like Marshall Nirenberg, Har Gobind Khorana, and others.