Chemistry of Life » The RNA Hypothesis

It is believed that before the coming of cellular life there was a gradual molecular evolution. The build up of complex chemicals was most likely catalysed by clays containing iron and smaller amounts of other metals. A strongly held opinion, known as the RNA Hypothesis suggests that simple molecules containing carbon, hydrogen, oxygen, nitrogen and phosphorus reacted at the catalytic surfaces of minerals, possibly clays, to form a group of large complex molecules called RIBONUCLEIC ACIDS (RNA). For this purpose energy was required and this was obtained from chemical reactions which took place in the environment and produced molecules of an energy carrying molecule. One of the most important energy donating chemicals even at this early stage of evolution was probably ADENOSINE TRIPHOSPHATE or ATP. According to the theory, these early forms of RNA acquired the capacity to catalyse the production of molecules identical to themselves without the need of inorganic substances such as the clays. The first stage of biochemical life began by the production of ‘daughter molecules’ identical to the ‘mother molecules’. Occasionally ‘mistakes’ were made in the copying mechanism giving rise to ‘mutant molecules’. Eventually there were a large number of different types of RNA competing with one another in the environment. Chemical evolution had begun. The RNA molecules were both the first biochemical catalysts (enzymes) and the first carriers of genetic messages.

Further stages in this pre-biotic chemical evolution eventually resulted in the synthesis of proteins and DNA. The proteins were more efficient catalysts than RNA and took over the enzyme functions. Another change that occurred was that DNA took over the genetic role. DNA differs from RNA in that it uses DEOXYRIBOSE instead of ribose And THYMINE (T) instead of uracil and is double stranded.

An even more recent theory suggests that the first self-replicating molecules did not belong to the RNA group but to a group of related chemicals called PEPTIDE NUCLEIC ACIDS or PNA. These are a kind of hybrid group of molecules in between RNA and proteins in which the sugar ribose is replaced by peptide links attached to the A, G, C and U bases. Unlike RNA these compounds are stable at 100oC. It is likely that the early Earth was very hot. Also black smokers are surrounded by extremely hot water.

It is supposed that at some stage the RNA, DNA and proteins were encapsulated in protected membranes and simple cellular life began.

'Variations on a Theme' lead to Astrobiology concerned with similarities and differences that may occur in that wonderful chemistry we call life on other planets in this stupendous Universe.

Ray Goodwin

Somewhere there are mountains
Glistening in the snow
Somewhere there are mountains
That we shall never know

Somewhere there are rivers
Flowing fast and free
Somewhere there are rivers
That we can never see

Somewhere there are oceans
And sun drenched island sands
Forests full of creatures
In vastly distant lands

Somewhere there’s a planet
Beneath an alien star
The people watch our tiny sun
And wonder where we are

One day perhaps we’ll find them
Across the void of space
Perhaps through ways as yet unknown
We’ll meet them face to face

The author of this web site Ray Goodwin holds B.Sc. Degrees from London University in Chemistry, Geology and Physiology and an M.Sc. in Biochemistry. He has spent most of his professional life teaching in Colleges of Technology. On his retirement he has entered the fields of astronomy, astrochemistry, astrobiology and space sciences. He has spent a great deal of his retirement in visiting amateur astronomy societies and in attending European Space Agency Symposia in ESTEC in the Netherlands and other scientific conferences in England and Sweden. He regularly attends the yearly European Astrofest in South Kensington London and other meetings in the UK. He has written scientific articles and given a number of lectures on diverse scientific subjects.

Readers of this web site are invited to e-mail the author ( and discuss their opinions of the topics dealt with and suggest any changes which they think may be helpful.

Life in the Cosmos Website
Version 01.00 - April 20, 2015.