20 - 004 What is DNA ?

The DNA master plan for life has now been transcribed into a computer digital file. It can be read and it can be copied and it can be changed. It can now be represented as computer file. No different from a computer text file or picture file. The work undertaken by Francis Crick and James Watson back in 1953 took the molecule deoxyribonucleic acid (DNA) as a chemical analysing it deeper down to the smaller chemical components of adenine (A), thymine (T), guanine (G) and cytosine (C). But significantly they then spotted a pattern whereby A fitted neatly with T and G fitted neatly with C forming two pairs with the molecule consisting of two chains linked together by A-T and G-C pairs. This pattern was the way hereditary information was stored in each DNA molecule with each of these DNA molecules existing within each living cell. Now these DNA patterns can be divided up into bits of similar looking smaller patterns which got repeated a lot and these got referred to as genes the study of which was called genetics. So it became possible to isolate different types of gene. These genes could be linked to the finished life cells in living organisms each having their own particular purpose. So whilst you can go right down to an individual gene all these could be put together to form the complete plan to make a specific life. So when you have got the complete plan for a life it is called a genome. So the genome for a flower or rabbit or fish or human. The human genome has obviously been one of greatest interest to us as intelligent humans. So what does the plan look like to make a human being. But at the same time we have been very interested in life forms that want to kill us. So the bacteria genome and virus genome have become of particular interest particularly with the threat of a killer virus that can cause a pandemic. Something that could destroy the whole human race. What it is important to appreciate is that DNA is only the master plan. It is only like the plan that you would have for building a new house. You use the plan as guidance to building the new house. To make a life the DNA genome has to be read and converted into real chemical cells. In making a new life all this information is derived from the chromosomes which if you like have everything packaged up to plan for the steps necessary to build this life. The seed from which life begins. So this conversion process from the DNA plan to the real chemicals that make our cells goes through a number of stages. The final living cells are made up from molecules called amino acids with twenty standard amino acids like cell building blocks. So the four bases in DNA (A,T,G,C) are used in different combinations to define an intermediary ribonucleic acid (RNA) which is a simpler than DNA having only one backbone. It is more like a step by step recipe of what needs to be mixed together to make the final living cell. This step between DNA and RNA and the creation of the final living chemical cell has been called epigenetics which we will look at later in the book. What is important for now is you have appreciated that DNA is just the plan for defining the components of life (genes) in a defined pattern format (digital file). The DNA genome is the total pattern format plan (digital file) for a whole life of something like a rabbit or human being.