Let´s continue with the epigenetics topic. In part 1, I introduced you to epigenetics and I told you how amazed I was when I first heard about it during my undergrad years. Up until that point, I had always thought that genetics controlled every aspect of an organism. But during the early years of my undergrad studies, I found out that this was not the case. There was something called epigenetics. In contrast to genetic changes, which involve alterations of the DNA sequence (mutations), epigenetic changes do not. If you remember, epigenetic changes are when chemical tags, known as methyl groups, are attached to the DNA. These tags affect the properties of the DNA, without altering its sequence. When these tags are present on the DNA, genes are turned off. However, as with most things in science, this is not the whole story.
In a previous post, I mentioned that the DNA consists of four different molecules, attached to each other to form long strands of DNA molecules. There are 46 DNA molecules in a cell. If one would stretch out and add up the lengths of every DNA molecule, it would reach over 2 m. That´s a lot of DNA inside one tiny cell. The reason why all this DNA can fit inside a small cell is thanks to a group of proteins known as histones. The long strands of DNA molecules in the cell nucleus are tightly wrapped around the histone proteins. This reduces the space that the DNA occupies and therefore enables all the DNA molecules to fit inside the cell. Though this is good, it also poses a problem. Because the DNA is so tightly wrapped around the histone proteins, it prevents the genes to be turned on. In order for genes to be turned on, the DNA must be loosened. It is here where the chemical tags come into the picture again. Just like with the DNA, histones can be chemically tagged as well. But in contrast to the DNA, histones can be tagged with a larger variety of tags (methyl, acetyl, phosphate tags and many more). It is the combination of the tags, their amount and location on the histone proteins that determines how tight the DNA is wrapped around the histone proteins and ultimately whether genes are turned on or off.
Attachment and removal of the tags is a highly dynamic process, it can occur within a matter of seconds. The impact of epigenetics on human biology is perfectly illustrated in genetically identical twins. Initially, genetically identical twins might look identical, but as they grow older, their appearance starts to differ from each other. As mentioned in part 1, epigenetics is highly influenced by our life style. As each of the twins grows older, they start to adopt their own life style. Consequently, this affects their epigenetics differently and ultimately their appearance, even though they have identical genetics. So as you can see, epigenetics plays a huge role in the biology of an organism. More so than genetics. So like I said before, life is not all about genetics.