Chromosomes, Euchromatin, and DNA

We all know that our body is made up of millions of cells, each cell makes up the structural and functional unit of life. Each cell consists of many cellular organelles such as nucleus, mitochondria, lysosome, etc.

Chromosomes are one of the important components which are present in the nucleus of the cell and contains an organized package of DNA, which is very much important in carrying out the body’s metabolic and enzymatic activities and also has a vital role in carrying out the hereditary characters.

Chromatin is one of the complexes of the DNA and proteins which forms the chromosomes.

Chromatin, a complex of DNA and proteins which forms the chromosomes with the nucleus of the eukaryotic cells, where the Nuclear DNA does not appear in the form of free strands, rather it is highly condensed and winded around the nuclear proteins to get fit inside the nucleus.

Chromatin generally occurs in two forms, namely euchromatin and heterochromatin.

Euchromatin is less condensed and can be transcribed, whereas the heterochromatin is highly condensed and is not typically transcribed.

What is Euchromatin?

Euchromatin is one of the types of chromatin, which is slightly packed in a condensed form’ which contains structural genes along with it and it is usually transcriptionally active.

It is the genetically active region of the chromosome, which contains structural genes that are replicated during G1 phase and S phase of the interphase which allows the polymerases to access the genes.

It also gives accesses to the RNA gene regulatory proteins and the complexes of RNA polymerases which gives access to the genes to be transcribed into mRNA, the euchromatin regions are always accessible for the process of transcription for the housekeeping genes.

These genes are very much essential for the basic function and the survival of the cell. G-band techniques helps in enabling the visualization and distinction between the euchromatin and heterochromatin regions which are present in the chromosomes.

Euchromatin is always stained lightly where as the heterochromatin stains darkly. The lighter staining of the Euchromatin is due to their slightly packed structure of chromatin.

It is a lightly packed form of chromatin which is enriched with genes and is often active but it is not always active.

It has the most active portion of the genome present within the cell nucleus. Humans contain almost 92% of their cells as euchromatin.

Structure of Euchromatin

Euchromatin has a reminiscent structure which has an unfolded set of beads on a string, where as those beads represents the nucleosomes.

Nucleosomes has eight proteins which are known as histones, which are made up of approximately 147 base pairs of DNA winds around them, in euchromatin this wrapping is loose, so the raw DNA may get accessed.

Each core histone posses a tail like structure, which varies in several ways, it is said that these variations act as a master control switches which determines the over all arrangement of the chromatin.

Particularly it is believed that the presence of methylated lysine four on the tail of the histone acts a general marker. The euchromatin is generally found with its appearance that it has a light color bands which when stained with G-banding techniques, and observed under an optical microscope, it appears opposite to that of the hetero chromatin as heterochromatin have a darker stain.

This lighter staining of the euchromatin is due to the less compact structure which is due to the loosely condensed fibers.

The basic structure of euchromatin is an elongated and fiber which has a size of about 10nm, which looks like microfibrils; when observed under an electron microscope.

Usually in prokaryotes, chromatin is present only in the form of euchromatin and hetero chromatin is absent.

It is also said that heterochromatin structure evolved lately in the nucleus of the cell, which acts as a mechanism to handle the increasing size of the genome.

Function of Euchromatin

Generally, Histone modifications contributes the regulation of DNA transcription. Whereas the genes present in the heterochromatin are not accessible for transcription.

Acetylation promotes the formation of the euchromatin which allows the transcription of the genes.

It helps in active transcription of DNA to mRNA products.

The unfolded structure of euchromatin helps in allowing the gene regulatory proteins and RNA polymerase complexes to bind the DNA sequences.

This initiates the process of transcription. It is also important to know that not all euchromatins are necessarily transcribed, but in general the genes which are non-transcribed are transformed into heterochromatins, these heterochromatins protect the genes when they are not in use.

This is how there is a direct link between the actively producing cell and the amount of euchromatin which can be found in the nucleus.

It is said that the cells uses transformation for converting euchromatin into heterochromatin as method to control the process of expression of genes and in replication, because these processes behave differently on a densely packed or compacted form of chromatin which is known as accessibility hypothesis.

One such hypothesis of the consecutive euchromatin is that it always turns the housekeeping genes, which helps in coding the proteins which are needed for the basic functions of the survival of the cell.