Answer:
glycine
Step-by-step explanation:
Polynucleotide phosphorylase is an enzyme that can synthesize RNA in the absence of a DNA template. In the experiment you described, if researchers added this enzyme to a large quantity of only guanine (G) ribonucleoside diphosphates (GDP), the RNA molecule produced would consist solely of guanine (G) bases. In the genetic code, guanine (G) codes for the amino acid glycine.