RNA world

All modern organisms have DNA as a store of genetic information, RNA as a message and proteins as their major cellular catalyst. This shows that the organism from which all cellular life began had these properties, which is called 'LUCA', meaning Last Universal Common Ancestor. This is a very complicated model and there are many questions surrounding the origin of life, for example, how did it all start? Where did DNA come from, as proteins are involved in its replication? DNA codes for proteins, so how can proteins have been produced first, as they are believed to have been? What came first - polynucleotides or polypeptides?

 The RNA world is the currently accepted hypothesis which answers these questions. This is based around the idea that RNA, as a message, led to proteins (this stage can be referred to as the RNP world), which became catalysts. This led to DNA, the store of genetic information. However the exact specificity of how this came about is still unclear. One concept is that life came from meteorites from outer space, as they have been observed to carry water, organic carbon and biomolecules including amino acids. A similar concept is that life originates from deep sea vents, due to high hydrogen sulphide and mineral levels. One of the most popular concepts is that the early atmosphere composing of water, methane, ammonia and hydrogen went on to produce the core biomolecules. This was demonstrated by Stanley Miller, who formulated an experiment mimicking the conditions of the early atmosphere discovered that after only a week 10-15% of the carbon was found to be part of organic compounds, 2% of that being amino acids.

Evidence supporting the RNA world

RNA can behave as both a store of genetic information and as a cellular catalyst.

RNA is capable of replicating itself without the use of enzymes.

It is more likely that a single molecule was capable of replicating itself, rather than two different molecules being synthesised by random chemical reactions in the same place, at the same time.

Ribosomes use RNA to catalyse pepide bond formation of amino acids in DNA.

The RNA world could easily have evolved into our current day mechanism of storing genetic information, but it is unlikely that an efficient system of self-replicating molcules could have been added to with RNA.