Chromatin is condensed DNA in the nucleus of a cell that is regulated by mechanisms for gene function. Methylation is a common process for chromatin formation, and it can lead to the inactivation of an entire chromosome. Accessing condensed DNA involves chromatin remodeling, which is important for gene translation and cell function.
Chromatin, also called heterochromatin, is the DNA in the nucleus of a cell that has been condensed and sometimes modified to a relatively inactive state. Most of the majority of human DNA exists in this condensed state at any given time, which allows its more than six-foot length to fit within the microscopic boundary of the nucleus. DNA condensation is not a random event, and special mechanisms in the cell carefully regulate the condensation and relaxation of nucleic acids, depending on which genes are required for cell function at any given time. These mechanisms handle actions including DNA unwinding, gene site identification, and DNA repair, and each involve their own proteins and enzymes.
The formation of chromatin commonly occurs by a process called methylation, in which groups of atoms called methyl groups are added to DNA. This is not the only DNA modification that can stimulate chromatin formation, but it is one of the most common. Methylation signals that a particular region of DNA shouldn’t be read or used at all at the moment, so it should coil up in its condensed form until it’s needed again. DNA condensation does not happen due to methylation alone because other proteins and molecules are involved, but methylation is often the first step.
The process of chromatin formation can sometimes be so extensive that an entire chromosome is essentially inactivated. This occurs frequently in animals where two X chromosomes designate the development of a female. An X chromosome in each cell is randomly deactivated by condensing into chromatin without harm to the body. This inactivation of the X chromosome is the reason for the random patches of fur color on tortoiseshell cats; the coat color gene is on the X chromosome and the color that is expressed depends on the active chromosome. The condensed chromosome, often called the Barr body, may be completely inactive but often retains a small measure of activity.
Accessing DNA that has been condensed into chromatin is often a two-pronged process, involving rearranging the condensed DNA and removing any changes that previously signaled the condensation. The release of condensed DNA is called chromatin remodeling and can occur very rapidly, usually within thousandths or millionths of a second. The resulting structure of the released DNA is very important to how genes are read and translated. The mixing between condensed and accessible DNA is essential for the proper functioning of a cell, and these transitions occur millions of times every second in the human body.
Protect your devices with Threat Protection by NordVPN
