Final answer:
Three "letters" or nucleotides of an RNA molecule are needed to code for a single amino acid, making up a codon which is essential for protein synthesis.
Step-by-step explanation:
The question pertains to the genetic code and how it is transcribed from RNA to produce amino acids.
To answer the question: How many "letters" of an RNA molecule, in sequence, does it take to provide the code for a single amino acid? The correct answer is C. 3.
This corresponds to a codon in the genetic code. Every three nucleotides, or "letters," in an RNA sequence specify one amino acid, forming part of a protein.
This triplet code is crucial for the translation process during protein synthesis.