The First Cells

Forming biologically relevant molecules in the primitive earth would have been the first step on the road to forming the first primitive cells. Possibly random proteins and greasy lipid molecules collected around the primeval RNA (or DNA), so forming a microscopic membrane-covered organic blob. Eventually this proto-cell learned how to use RNA to code for its protein sequences. The lipids formed a membrane around the outside to keep the other components together. Early on, protein and RNA

FIGURE 20.06 Artificial Evolution of Ribozyme RNA Polymerase

A random pool of RNA was generated and screened for the ability to seal a nick in one strand of a broken piece of double-stranded RNA. Occasional random molecules of RNA that had this enzymatic activity were found and isolated. Through successive rounds of mutation and selection, this primitive ribozyme was altered just enough to actually catalyze the elongation of the RNA using a single-stranded template with a primer. Unlike true protein RNA polymerases, the RNA polymerizing ribozyme only added one nucleotide at a time, dissociating after each addition.

dom pool of RNA

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