Question: What is DNA and where dose it come from?

Jim Caryl answered on 21 Jun 2011:

DNA is the chemical in your your cells that encodes all the information that is required to make, well, *you*!

The science bit….

It stands for deoxyribonucleic acid, which basically means that it is strings of nucleic acids joined together by special (ribose) sugar molecules (not quite the same sort of sugar that you’d put in your tea though), and phosphate molecules – these form the backbone scaffold that holds the nucleic acids. DNA exists as two strands, which form a helix (the so-called ‘double helix’), and the two strands are held together by the nucleic acids on one strand holding hands with their partners on the other strand; there are four different nucleic acid bases that make up DNA: adenine, which pairs with thymine, and cytosine which pairs with guanine. DNA is the long-term storage device holding the ‘blue-print’ of how to make *you*, and the information is encoded by the order in which the nucleic acids are joined togehter – the DNA sequence.

Whilst you have LOADS of DNA in every cell, it is so well twisted and coiled and wrapped around that it is compacted into a little sack in your cells called an nucleus – though in bacteria it is attached to the inside of the the bacterial cell’s skin (cell wall).

The story bit…

The big question is, where does it come from? Think about it this way. over 3.5 billion years ago, the DNA that existed in the earliest form of life – even things that you would struggle to recognise as ‘life’ – was replicating itself. The DNA kept replicating, and replicating and in fact has never stopped making more of itself EVER for the last 3.5 billions years.

Like a game of Chinese whispers it has tried to stay the same, and yet curiously, some small mutations actually make it do better than without, so these stick around and keep happening from time to time. As time has passed, more DNA has been added on to those early molecules, and the DNA has found new environments to live in, surrounded itself with different and increasingly complex ‘cells’ and continued to refine the way in which it makes more of itself and how it packages up all the increasing length it has.

This has continued in an unbroken chain throughout all of history. Despite all the many cataclysms the Earth has seen, somewhere your DNA – or at least the DNA that would become you one day – was busy replicating. You wouldn’t recognise it now though, because it’s part of a complex animal, a great new environment for the DNA to continue replicating. A few million years ago a small ape started on a course to become human (not that it knew this at the time), but eventually it would evolve into something that we would recognise as human – the whole time, the DNA inside the cells continued to replicate more of itself.

Finally, in this unbroken chain of successful DNA replication, your mother and father combined their DNA, bits of DNA that are highly related (as all humans are) and this resulted in you. You are the sum product of 3.5 billion years of successful, unending and uninterrupted DNA replication, which is a) something to be pretty proud of, and b) something totally worth trying to understand and study 😉