The Surfaces of the Two Ribosomal Subunits That Face One

Multiple Choice

The surfaces of the two ribosomal subunits that face one another contain the binding sites for the mRNA and incoming tRNAs and are thus key for the function of the ribosomes. The fact that these surfaces consist largely of RNA supports what proposal?

A) primordial ribosomes were composed solely of proteins
B) primordial ribosomes were composed exclusively of RNA
C) primordial ribosomes were composed exclusively of DNA
D) prokaryotes gave rise to eukaryotes
E) endosymbiosis gave rise to eukaryotes