The key difference between heterochromatin and euchromatin is that heterochromatin is the highly packed form of chromatin which is generally inactive while euchromatin is the loosely packed form of chromatin which is generally active.
Chromatin is the structure that holds the DNA strand of a chromosome. Heterochromatin and euchromatin are the two main types of chromatin that are present in the cells. There is a difference between heterochromatin and euchromatin in terms of structure and function. In addition, they differ from the transcription and replication properties as well.
CONTENTS
1. Overview and Key Difference
2. What is Heterochromatin
3. What is Euchromatin
4. Similarities Between Heterochromatin and Euchromatin
5. Side by Side Comparison – Heterochromatin vs Euchromatin in Tabular Form
6. Summary
What is Heterochromatin?
Heterochromatin is the tightly packed form of chromatin present in the cells of eukaryotes. It is usually present at the periphery of the nucleus. Due to its highly packed nature, it is visible during the staining of DNA of a cell. Also, this intensely stained DNA has two types; they are the constitutive and facultative heterochromatin. Constitutive heterochromatin is basically responsible for forming the centromere or the telomere while attracting signals for both gene expression and repression. Facultative heterochromatin becomes repetitive under special signals or environments; otherwise, it stays quiet with a highly condensed structure. The basic function of heterochromatin is to shelter the DNA strand. In addition, chromatin helps in gene regulation. When there is a DNA strand without heterochromatin, there is a possibility of endonucleases unnecessarily digesting that fragment.
Figure 01: Heterochromatin
Inheritance ensures the presence of heterochromatin in the next generation. Usually, the condensed structure of heterochromatin prevents unwanted gene expression until a specific signal arrives and informs to uncondense DNA in order to expose DNA strands for transcription. Usually, the replication of DNA in heterochromatin takes place in the latter stages. Its compact structure determines most of the functions in gene expression; in fact, it is sometimes called the gene silencing.
What is Euchromatin?
Euchromatin is the loosely-packed DNA sheltering structures in the cells. Usually, they are present towards the inner core of the nucleus. Euchromatin is present in both prokaryotes and eukaryotes. In fact, euchromatin is the only type of chromatin present in the prokaryotic genetic material. Moreover, its loosely packed structure causes less visibility during the DNA staining, unlike heterochromatin.
Figure 02: Euchromatin
The uncondensed nature of euchromatin is mainly due to the loose wrapping of histone proteins around the DNA strand. Therefore, the access of DNA is easy to initiate the DNA transcription. Moreover, euchromatin contains the most active genes of an organism. It is because euchromatin participates actively in the transcription of DNA into mRNA. Some euchromatins are not always transcribed but transformed into heterochromatin after the basic function to silence the genes. However, there are some ever active euchromatins to maintain the stability of the basic and essential processes for the survival of the cell.
What are the Similarities Between Heterochromatin and Euchromatin?
- Heterochromatin and euchromatin are two types of chromatin present in the eukaryotic cells.
- Both forms of chromatin are present in the nucleus.
- Moreover, they are complexes of DNA and proteins.
- And, both participate in DNA transcription.
- Also, they both are associated with histone proteins.
What is the Difference Between Heterochromatin and Euchromatin?
Heterochromatin and euchromatin are two varieties of chromatin present in living organisms. The key difference between heterochromatin and euchromatin is that the heterochromatin is the highly packed form of chromatin in the nucleus while euchromatin is the loosely packed form of chromatin in the nucleus. Generally, heterochromatin is inactive while euchromatin is active. Consequently, heterochromatin contains more DNA, while euchromatin contains less DNA. So, this is another significant difference between heterochromatin and euchromatin.
Furthermore, an important difference between heterochromatin and euchromatin is that heterochromatin is less abundant. But, around 90% of the total human genome is euchromatin. Besides, a further difference between heterochromatin and euchromatin is that heterochromatin is only present in eukaryotes, but, euchromatin is present in both prokaryotes and eukaryotes.
Summary – Heterochromatin vs Euchromatin
Heterochromatin and euchromatin are two types of chromatin. The key difference between heterochromatin and euchromatin is the packaging. Heterochromatin is the highly packed form of chromatin while euchromatin is the loosely packed form of chromatin. Hence, heterochromatin contains more DNA while euchromatin contains less DNA. But, heterochromatin is generally inactive while euchromatin is generally active. Thus, this is a summary of the difference between heterochromatin and euchromatin.
Reference:
1. “chromatin.” Nature News, Nature Publishing Group, Available here.
Image Courtesy:
1. “Sha-Boyer-Fig1-CCBy3.0” (CC BY 3.0) via Commons Wikimedia
2. “Mitoticchromosome” By HeavyQuark – Created on microsoft paint (CC BY-SA 3.0) via Commons Wikimedia