Molecular Biology of the Gene 7th Edition by Richard Losick, James Watson, Michael Levine, Tamara Baker, Alexander Gann

Exercise 3

Researchers studied the permeability of fatty acid vesicles as model protocells.
A. Explain why membrane permeability properties are important when considering the RNA World hypothesis.
B. In one experiment, the researchers encapsulated nucleotides within fatty acid vesicles. Instead of measuring permeability by detecting nucleotides entering the vesicle, they measured the percent of nucleotides from within the vesicle that left the vesicle. They found negligible loss of AMP, ADP, and ATP from the vesicles over a 24-hour period. In the presence of Mg 2+ , they found that AMP and ADP slowly leaked from the vesicles, but not ATP. Propose why AMP and ADP are able to cross the membrane in the presence of Mg 2+. What does the failure of ATP to cross the membrane in the presence of Mg 2+ suggest about the permeability of early protocells?