Chromatids are components of the chromosomes of eukaryotes and consist of a double strand of DNA and the associated proteins. Depending on the phase of the cell cycle, a chromosome consists of either one or two chromatids. They play a crucial role in cell division.
Chromatid structure and function
chromosomes contain the genetic information of a cell. A chromosome consists of either one (one chromatid chromosomes) or two chromatids (Two chromatid chromosome). The chromosomes and chromatids are located in the cell nucleus. Chromatids are formed when the genetic material (=DNA) of a cell is tightly packed before cell division.
Structure and formation of the chromatid
A chromatid consists of a coiled Chromatin fiber (=chromatin). The chromatin fibers settle out DNA and various skeletal proteins together. The fibers are created during the condensationif the DNA to specific proteins that histonesis wound.
In biology, the compression of the DNA into chromatids or chromosomes is referred to as condensation.
The coiling of the genetic material drastically reduces its length. The resulting ones nucleosomes combine to form a densely packed chromatin fiber.
The nucleosome is a unit made up of eight histone proteins and a piece of DNA wrapped around the histone proteins.
The chromatin is the storage form of the inheritance. In the cell nucleus, the chromatin is packed in different densities. Most of these are accessible to enzymes. The packaging can be loosened if necessary, for example if parts of the DNA have to be copied (=transcription).
During mitosis and meiosis, the chromatin fiber continues to condense, ultimately forming chromatids. A chromatid consists of exactly one double strand of DNA. The genetically identical chromatids of a chromosome, too sister chromatids called, accumulate and form a Two chromatid chromosome. During the metaphase of cell division, this is particularly visible under the microscope.
In the following figure you can see a schematic representation of the structure of a two-chromatid chromosome.
Figure 1: Structure of a two-chromatid chromosome, source: wikipedia.de
as centromere is the place where the two sister chromatids of the chromosome connect. The telomeres are the «ends» of the chromosome.
function of the chromatids
The chromosomes or chromatids are of great importance because they contain the entire genetic information of an individual. As you probably know, the genome is the blueprint of the body. It contains information about things like eye and hair color, but also the predisposition to suffer from certain diseases or allergies.
As you have already learned, the genome is mostly in the form of chromatin. However, the chromatin is difficult to transport to another cell. In order to ensure the transport and distribution of all genetic information to daughter cells, the chromatin condenses into chromatids. So chromatids and chromosomes are something like that transport form of the inheritance.
Chromatid during nuclear division
Most cells in the body undergo nuclear division by mitosis before cell division. The DNA in the cell nucleus is first duplicated (interphase). During the prophase compresses the chromatin so much that chromatids form. These combine to form chromosomes. During the metaphase the genome exists exclusively as two-chromatid chromosomes.
In the following anaphase the chromatids of the chromosome are separated. At this stage, the so-called spindle apparatus, which attaches to the centromere and pulls the chromatids in opposite directions. This ensures that each newly created cell nucleus receives the correct number of chromosomes.
The following figure shows you the separation of the chromatids:
Figure 2: Separation of the chromatids during the anaphase of mitosis, source: wikipedia.de
After the nuclear division, the chromosomes consist of only one chromatid, which is also called One chromatid chromosome is known. The chromosomes are then distributed to the daughter cells and decondense, i.e. loosen up again to form chromatin. Only when the cell is preparing for another division in its cell cycle does the DNA double again.
The cell cycle is the period of time between two cell divisions in eukaryotic cells. Various activities take place during the cell cycle that ensure the cell’s ability to divide.
In meiosis, on the other hand, the first step is reduction division. Here the sister chromatids are not separated, but the homologous chromosomes. Only in the second step does nuclear division take place via mitosis. This form only occurs in sex cells (=gamet).
Chromatid – The most important things at a glance
- The chromatid is part of the chromosome and contains the genetic information.
- The chromatids are made up of densely packed DNA and skeletal proteins.
- The genome condenses into chromatids when a cell division is imminent.
- Chromatids are the transport form of DNA.
- During cell division, two genetically identical sister chromatids combine to form a chromosome.
- A chromosome made up of two chromatids is called a two-chromatid chromosome.
- After cell division, the chromosomes are present as single chromatid chromosomes.