Question

Ice has also been observed to increase polymerization. This seems counter-intuitive because molecular motion decreases at colder temperatures. So how could freezing a solution actually increase reaction rates?

review Szostak and Battel’s experiment on RNA evolution. Put this process into Darwin’s 4 points.   

Explain the hypothetical genetic copying scenario outlined using convection currents in pools. How is this similar to PCR?

Answer 1

Scientists have studied the influence of freezing on the endothermic oxidation reaction of sulphide to sulphate in growing ice crystals inside a cloud chamber. Similarly, the oxidation reaction of nitrite to form nitrate, that is indeed a very slow process when in solution but is accelerated markedly when it occurs in a solution that undergoes freezing. In case of the freezing of dilute ionic solution, the differences in the partitioning of ions in the aqueous and ice phases can generate electric potentials that may accelerate electrochemical reactions.

In an in vitro experiment, David Bartel and Jack Szostak (1993) isolated “class I” catalytic RNAs (ribozymes) from a large pool of random-sequence RNA molecules, which is analogous to RNA-catalyzed RNA polymerase proteins. These ribozymes are robust enzymes that are able to ligate two RNA molecules that are aligned on a template by catalyzing the attack of a 3'-hydroxyl on an adjacent 5'-triphosphate. The corresponding uncatalyzed reaction also gives rise to a 3',5'-phosphodiester bond and this reaction rate is exceeded by the reaction rates of ribozymes which are 7 million times faster.  The chemical basis for Darwinian evolution based on natural selection could be explained by RNA-dependent RNA replication given by Szostak and Bartel's experiment. Darwinian evolution focuses on identifying simple cellular systems that are both autonomously replicating and subject to natural selection. Interestingly, an RNA molecule which can act both as a template for the storage and transmission of genetic information, and as an enzyme- RNA polymerase that can replicate its own sequence representing the key component in any cell. A simple cell with a membrane-bound interdependent genome (Such as RNA) would be a sustainable, and able to replicate autonomously and capable of Darwinian evolution.