Self and the Beginning of Life 41“9x6” b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to HumanityRNA chains have been formed under relatively mild temperature
(40–90°C).^263.9 Evidence against RNA: (I) Making an RNA Molecule
Proves Daunting
Careful analysis reveals serious problems facing the RNA World hypoth-
esis, foremost among which is the difficulty of making an RNA polymer
without the help of protein enzymes:
(1) Although synthesizing ribose sugar in the laboratory is not hard, the
newly formed ribose is unstable. Ribose can be made by reacting
formaldehyde and glycolaldehyde, both found in interstellar space
and probably on early Earth. It can also be formed by ultraviolet
light irradiation of a mixture of water (ice), methanol and ammo-
nia, all present in the formative stage of the solar system.^27 However,
ribose decomposes very quickly unless it is stabilized by complexing
with borate, a compound which is unlikely to be present in abun-
dance in the prebiotic environment.^28
(2) How were nucleobases synthesized spontaneously? Although purines
are comparatively simple to synthesize chemically, the pyrimidine
cytosine poses an insurmountable problem. Cytosine has never been
detected in meteorites, and it is not produced in spark discharge
experiments. The proposed prebiotic precursors (cyanoacetylene,
cyanoacetaldehyde, cyanate, cyanogen and urea) were unlikely to be
available in sufficient concentrations, and they were more likely to
undergo side reactions with other organic compounds than form the
desired product. And finally, cytosine, if formed, was too unstable
(hydrolyzed to uracil) to last long enough over the alleged geological
time for its incorporation into RNA.^29
(3) Under plausible prebiotic conditions, joining nucleobases with ribose
is fraught with problems. The reaction with purine nucleobases is
extremely difficult and the reaction with pyrimidine nucleobases