Four essential organic compounds

Four essential organic compounds, A - adenine, T - thymine, C - cytosine, and G - guanine, are organized into base pairs that form the double helix structure of DNA. The human genome—the DNA contained in the nuclei of our body cells—comprises 23 pairs of chromosomes containing strands of genes. DNA is wound around histones (a protein material) to form what resembles beads on a string, called the nucleosomes. Deposited along the nucleosomes are epigenetic markers, which, collectively, make up the epigenome. Epigenetic markers control gene expression by either opening up or tightly packing nucleosome clusters (chromatin). When chromatin is loosely spaced, gene expression is possible, but when chromatin is tightly packed, genes are silenced. Thus, when epigenetic markers signal chromatin to open, genes (segments of DNA base pairs) are ready to be transcribed and translated into proteins.