Difference Between Heterochromatin and Euchromatin

The human body is composed of billions of cells. A cell consists of a nucleus which has chromatin. According to biochemist scientists, the chromatin is the combination of DNA, RNA, and protein extracted from eukaryotic lysed interphase nuclei. Chromatin is responsible for packaging DNA into small volumes so that they can fit inside the cell. It also helps in strengthening the DNA for mitosis and miosis to take place. It also prevents DNA damage and controls the gene expression and replication of the DNA. Chromatin is classified into two groups; heterochromatin and euchromatin. Emil Heitz coined these two terms in the year 1928.

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The main difference between heterochromatin and euchromatin is that heterochromatin is such part of the chromosomes, which is tightly packed, genetically inactive, and found at the periphery of the nucleus. In contrast, euchromatin is an uncoiled packed form of chromatin, genetically active and found at the inner part of the nucleus.

When one observes the non-dividing cells of the nucleus under the light microscope, it shows two regions, on the ground of the concentration or the intensity of staining. The dark stained regions are said as heterochromatin and light stained areas are called euchromatin.

Comparison Chart

Basis for Comparison Heterochromatin Euchromatin
Definition Heterochromatin can be defined as the tightly packed form of DNA in the chromosomes Euchromatin can be defined as the loosely packed form of DNA in the chromosomes.
Cell Type Eukaryotes Prokaryotes and Eukaryotes
DNA density High DNA density Low DNA density
Shape Tightly pack form of chromosome Uncoiled form of chromatin
Kind of stain Stained dark Lightly stained
Location These are present at the periphery of the nucleus in eukaryotes These are present in the inner body of the nucleus of prokaryotes and eukaryotes.
Transcriptional Activity Show little or no transcriptional activity Actively participate in the transcriptional activity
Genetic Activity Genetically inactive Genetically active
Stickness Sticky Non-sticky
DNA replication Heterochromatin replicates later Euchromatin replicates early
Types Two types:

1.     Constitutive heterochromatin

2.     Facultative heterochromatin

Uniform euchromatin
Function Regulation of structural integrity and gene expression Genetic transcription and genetic variation

What is Heterochromatin?

Heterochromatin is an area of the chromosomes which are intensely stained with DNA specific strains. These are a tightly packed form of the DNA in the nucleus.

The proteins which are engaged in the gene expression are inaccessible by the heterochromatin because of the compacted nature of the heterochromatin. Because of this reason, chromosomal crossing over is also not possible and as a result, heterochromatin is not transcriptionally and genetically active.

Heterochromatin is divided into two groups; facultative heterochromatin and constitutive heterochromatin. The genes which get silenced by the process of Histone methylation or siRNA through RNA I are called facultative heterochromatin. So, they comprise inactive genes and is not a permanent character of every nucleus of the cells.

While the repetitive and structurally functional genes such as telomeres or centromeres are called constitutive heterochromatin, these are the continuing nature of the nucleus of the cell and contain no gene in their genome. This structure is retainable in the interphase of the cell.

The function of the heterochromatin is to protect the DNA from the endonuclease damage because of the compact nature. It also prevents the DNA regions from getting access to proteins during gene expression.

What is Euchromatin?

The which is rich in gene concentrations and is a type of chromatin loosely packed is called euchromatin. They are active during transcription. Euchromatin composes almost 90%of the entire human genome and covers the maximum part of the dynamic genome of the inner nucleus. Under a light microscope, its parts can be observed as loops that seem to have 40 to 100 kb areas of DNA in it. Under a microscope, it appears as light-colored bands. The diameter of the euchromatin fiber is about 30 nm.

To permit the transcription, some parts of the genome containing active genes are loosely packed. The loose wrapping of the DNA makes it available at the time of the process. The structure of euchromatin is similar to nucleosomes, which contains histones proteins having around 147 base pairs of DNAs wrapped around them.

The function of the euchromatin is to participate in the transcription of DNA to RNA. The gene-regulating mechanism is the process of transforming euchromatin into heterochromatin or vice versa. The active genes of euchromatin get transcribed to make mRNA, whereas further encoding the functional proteins is the major function of euchromatin. This is the reason that euchromatin is called genetically and transcriptionally active. Housekeeping genes are one of the types of euchromatin.

Key Differences

  1. Heterochromatin is the tightly packed form of DNA, whereas euchromatin is the loosely packed form of DNA in the chromosome.
  2. The density of DNA is high in heterochromatin, whereas the density of DNA is low in the euchromatin.
  3. Heterochromatin is stained dark under the microscope, whereas euchromatin is lightly stained under the microscope.
  4. Heterochromatin is located at the periphery of the nucleus in the eukaryotic cells. In contrast, euchromatin is located in the inner body of the nucleus in both prokaryotic cells and eukaryotic cells.
  5. Heterochromatin is genetically inactive, whereas euchromatin is genetically active.
  6. Heterochromatin has sticky regions, whereas euchromatin has non-sticky parts.
  7. Heterochromatin is tightly coiled and shows late replication, whereas euchromatin is loosely coiled and shows early replication.
  8. In heterochromatin, the phenotype remains unchanged whereas, in euchromatin, the phenotype shows variations.
  9. Heterochromatin allows the gene expression regulation and maintains the structural integrity of the cell, whereas euchromatin shows genetic variations and permits the genetic transcription.

Conclusion

In conclusion, both heterochromatin and euchromatin are a type of DNA in the chromosomes. The main difference is that heterochromatin is the densely packed form of DNA, whereas euchromatin is the loosely packed DNA in the chromosomes.

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