(Noun. kro-MUH-tin)
by Claire Olson
What does it mean?
If all of the DNA in an individual cell were fully stretched out, it would be about 2 meters long. By contrast, most cells have a diameter of only a few micrometers. To condense all that DNA into a single cell, it is wrapped around proteins called histones. Each unit of DNA wrapped around histones is called a nucleosome, and a complex of nucleosomes is called chromatin.
How do I use it in a sentence?
“For a gene to be expressed, the chromatin must be opened for transcriptional machinery to access the gene.”
“When chromatin is highly condensed, genes are not accessible for transcription.”
Schematic of chromatin at multiple levels of organization. From right to left: a DNA molecule (blue double helix structure) wraps around histone proteins (blue circular structures), forming chromatin with a structure resembling “beads on a string”. Chromatin can be further condensed to form a chromosome (blue X-shaped structure). Figure created by the author using BioRender.com.
Etymology
The term “chromatin” was established by Walter Flemming in the 1880s. He observed a material in the nucleus that readily absorbed certain dyes, making it visible under the microscope. He named the material “chromatin” from the Greek root “chroma”, meaning color. It was later discovered that chromatin is made up of DNA and histone proteins.
Related terms
Chromosome
Misconceptions (about word usage)
Two similar, commonly confused terms are “chromatin” and “chromosome”. “Chromatin” is a general term for the genetic material of DNA wrapped around histone proteins. A “chromosome” is a single strand of chromatin that is highly condensed into rod-shaped or X-shaped structures during cell division.
Fields of study in which this word is commonly used:
Genetics
Epigenetics
Molecular Biology
Biochemistry
Genomics
