http://www.scientificamerican.com/article/human-genome-s-spirals-loops-and-globules-come-into-4-d-view-video/

Ok, DNA is made up of deoxyribonuleic acid and is in the shape of a double helix, like those helical staircases we sometimes see in modern houses, we had one in my house when I was a young adult. DNA is composed of a deoxyribose (a sugar) backbone and it has four bases (Adenine, Thymine, Cytosine, Guanine) that form the rungs of the double helical stairs. Adenine only binds to Thymine, and Guanine only binds to Cytosine. So these bases are said to be complementary to each other. There are 2 meters of DNA in every nucleus of every cell in our bodies. Stretch out all the DNA in all our cells, it can go to the sun and back 50 times! Sort of unfathomable! Now the nucleus is only 3-10 micrometers in size! That’s 3-10 x 10 ^-6  meters!!! Fitting that much DNA in a cell nucleus (average width: 5 micrometers) is like fitting a string the length of the Empire State building underneath your fingernail! How does all this DNA (2 meters) fit into this tiny nucleus? One word: Chromatin. Chromatin is DNA coiled around itself and then coiled around eight proteins called histones. The DNA wrapped around Histones is called an octamer and is repeated over and over again the length of the DNA. Acetylation, phosphorylation and methylation of histones, known as epigenetic changes, because they are not changes to the sequence of the DNA, but changes to molecules associated with the DNA, these epigenetic changes alter how tightly the DNA binds to the histones. This also changes how active the associated gene is. If a histone is bound very tightly to the DNA, the enzymes that need to transcribe a gene (RNA Polymerases) can’t get to the gene. If the RNA Polymerase can’t get to the gene, then it cannot transcribe a copy of the gene into RNA. This then cannot be translated into a protein. So this gene is not active. Now if the histone were acetylated, it wouldn’t be so tightly bound to the gene, then the RNA Polymerase would have no problem transcribing the gene into a messenger RNA, which would then be translated into a protein by ribosomes. Now this gene is active.

The way genes act is, as I said above, first RNA Polymerase, which is an enzyme, makes a very faithful copy of the DNA gene into a messenger RNA, then the messenger RNA leaves the nucleus and goes to the cytoplasm, there it is used as the template to make a protein by these organelles (little organs haha) called ribosomes. So the end result is that the gene which is DNA, is finally translated into a protein. If this is a skin cell for example, the DNA will have melanin genes and they will be transcribed into RNA and translated into Melanin in your skin. This is how genes exert their effect. This is why we are what our genes make us. There is so much complexity inside the cell and inside the nucleus of a cell. Researchers have found that there are loops in DNA, areas of DNA normally far apart, brought together through loop formation! The genes in the loop are activated. Different regions of the chromosomes come together when loops are formed and these affect how active these gene are!

It’s endlessly fascinating and complex.