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	Podcast:		25. Early Earth and Life Processes
	Episode:		Replacing Molecules
	Category:		Science & Medicine
	Duration:		00:01:03
	Publish Date:		2011-07-28 08:51:58
	Description:		Transcript: DNA was probably too complex to have been the first replicating molecule in the history of life. RNA is much simpler. It has only one strand, and it would be easier to construct from smaller pieces. However, neither molecule can reproduce itself without enzymes. Enzymes are proteins that take their instructions from the DNA itself which leads to a classic chicken and egg problem. This problem was solved in the 1980s by Thomas Cech who showed that RNA can catalyze biochemical reactions in the same way that enzymes do leading to the probability that RNA could facilitate its own replication. Thus, the early Earth may have been an RNA world where RNA was replicating and facilitating its own reactions. In the totality of biochemistry, there are other possible replicating molecules, and perhaps life elsewhere in the universe has used these.
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