Damaged DNA - what happens next?
The instruction manual at the heart of every cell is written in a four-letter code. The manual is huge. It comes in 23 volumes (chromosomes) and contains approximately 3 billion letters. We don't know exactly what all the code translates to, but it turns out that a lot of our DNA either provides instruction on how to build the cell's personnel, or provides instructions on which bits of code to use when.
The cell's personnel are called proteins - they are either workers who get jobs done (enzymes), or management who come together and make decisions about what to do next (regulatory proteins). In any case, proteins are made by piecing lots of small building blocks together in the right order - like building a bike, or a car, or a house. The building blocks are called amino acids - each amino acid has a three-letter DNA code. So you read DNA in blocks of three. There are two special blocks of three 'ATG' which means 'start here' and 'TAA' which means 'stop here'. The following code:
Would therefore be split into threes and translated.
Start - A - B - C - Stop
A, B, and C are three amino acid building blocks which would be built into a chain. As the chain gets longer and longer it will turn into a protein - either a worker or management protein.
So how does this help us understand DNA damage?
Lewis Carroll invented a game called word ladders which features in the Alice in Wonderland novels. In the game a sequence of small changes to a word can lead to a big change – each change leaves a perfectly correct new word.
For example see how SLOW can become FAST ...
We can watch the same thing happen with DNA code. If we translate each of these words into DNA code we get:
In each case, one, two, or three of the DNA letters have been damaged and the cell has tried to repair them: it's tried, but got them wrong. As the damage is done and badly repaired the meaning of the instruction has slowly changed.
It's worth remembering that badly repaired damage is rare. You cells normally get it right, so changing an instruction could take years.
What you should be able to see is that relatively small changes in code build-up over time to give a complete change in character to an instruction - in this case an instruction 'SLOW' has become an instruction 'FAST'. There are two important things happening here: instructions can change as a result of small damage and mis-repair events; but also note that these changes can not just result in changes, but in completely reversing the sense of the instruction.
When we think about cancer, there are seven key chapters in the instruction manual. Each of these chapters deals with key elements in being part of a team. It's really important that cells work together in teams. If a cell loses the instructions for being part of a team then this can result in a disease that we call cancer.
We have seen how damage can change an instruction. Follow this link to find out about what happens when the team-work chapters of our instruction manual are damaged.