Last week I was chatting about the basic constituents of the body – quite literally what we’re made of, the elements and the working up of all the systems that join together. This week is a look at the controller of all that stuff – the thing that makes it all happen from our single fused-cell origins to the fully-formed trillions of cells we are today. Our deoxyribonucleic acid (DNA) sits protected in the nucleus of our cells and controls everything we are and everything the cell is and does. I’m sure describing DNA has been done a million times over, so I just want to make it a bit more understandable and tell you how amazing it actually is!
Below you’ll see what DNA actually looks like. It’s only when cells are ready to divide that it’s all coiled up tight into the chromosomes we’re used to seeing – it’s been twisted so much it’s called supercoiled.
It’s made of things called nucleic acids, attached to a backbone of sugars and phosphates. The nucleic acids are the letters of the genetic code, called Adenine, Thymine, Cytosine and Guanine. In one strand of DNA, there are all these letters and they match the other strand since A only binds with T and C only binds to G, the bits just chemically match up and they seem to like each other! See the image below, it shows you the chemistry of it all.
So great, there’s a big coiled bunch of chemicals held together in strands by this backbone. Crick and Watson theorized this shape it forms – the double helix. Now the fun comes with what all these letters do. When a bunch of letters together do something specific it’s called a gene; it “codes” for proteins. Basically, every three letters correspond to a specific building block – an amino acid. This means joining amino acids together in this specific order makes unique proteins. These fold up in unique ways too to eventually form proteins. It’s proteins that carry messages, give structure, virtually everything that makes cells and the body functional. Humans have about 20,000 genes that all encode proteins, which is a lot, but not really considering how many different functions cells have with all their unique components.
Cells can’t function properly if they don’t have DNA to make and control all the bits to keep it going. This is why there’s a security system in place to make sure that when it comes to making copies of itself, it’s only done if DNA is intact, without any changes being made to any of the letters – these are called mutations. So when the cycle comes round and it’s cell multiplying time, the DNA all condenses into the chromosomes we’re used to seeing. If there are any mutations it stops and will try repair it; if it can’t, it goes through a programmed cell death (apoptosis). If maverick cells ignore this, cells keep dividing until masses form – known as tumors, then certain criteria define it as cancerous.
So it’s pretty amazing stuff this DNA. It’s also true that we share most of it with our friends the chimpanzee. But there are a lot of “conserved sequences” which is why animal models are so useful in experimentation – if they make the same proteins as us, we can see the effects of its mutation or absence by following it around and seeing where it works and what it does. By tagging the proteins the sequence makes with something radioactive or fluorescent it can be tracked to see what’s going on. It’s been revolutionary in understanding countless mutations that can cause diseases and disorders.
Have a look below for the background of genetics and a summary of what DNA is and does. Meanwhile, since it’s summertime, go get some strawberries… and keep a few to extract some DNA for yourself! All you need is some salt, washing up liquid and ice cold rubbing alcohol/vodka. Look here for the instructions!