Final answer:
Histones, which are positively charged due to lysine and arginine residues, bind strongly to the negatively charged DNA due to opposite charges. Modifications like acetylation can decrease histone charge, reducing DNA-binding affinity, altering gene expression. Methylation tightens nucleosome packing and inhibits transcription factor binding, suppressing gene expression.
Step-by-step explanation:
The chemical properties of histones and DNA that enable these molecules to bind tightly together are largely due to their opposite charges. Histones are basic proteins that contain a high amount of lysine and arginine amino acids, which are positively charged. This positive charge allows them to bind to the acidic, negatively charged phosphodiester backbone of the double helical DNA. The nucleosome, which is the fundamental unit of chromatin, is composed of an octamer of histones (two of each of four different histones) around which DNA is wrapped tightly.
The tight association between histones and DNA can also be regulated by certain chemical modifications. For example, the addition of chemical groups such as methyl, acetyl, or phosphate groups to the histone proteins can change how tightly the DNA is wound around the histones. In particular, adding an acetyl group can reduce the positive charge of the histones, causing the DNA binding to become more relaxed. This process plays a crucial role in the regulation of gene expression as it can make certain regions of the DNA more accessible to transcription factors, thereby regulating whether genes are turned on or off.
Methylation of DNA and histones also plays a significant role in the regulation of gene expression. Methylation causes nucleosomes to pack tightly together, which prevents transcription factors from binding to the DNA and thus results in genes not being expressed. This form of chemical modification is essential for the proper functioning of cells, as it helps to control which genes are active at any given time.