Collegedunia Team Content Curator
Content Curator
Euchromatin and Heterochromatin are the two forms of Chromatin. Prokaryotic cells have only euchromatin whereas eukaryotic cells have both euchromatin and heterochromatin. Both euchromatin and heterochromatin have unique functions for cells. Let’s see the differences between Euchromatin and Heterochromatin.
| Table of Content |
Keyterms: Chromatin, Euchromatin, Heterochromatin, Prokaryotic cells, Eukaryotic cells, Cells, DNA, RNA, Protein, Transcription, mRNA, Genome
What is Euchromatin?
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Euchromatin is a form of chromatin that is lightly or loosely packed (DNA, RNA, and protein). Euchromatin is enriched with genes and often takes place in the active transcription of DNA to mRNA. It comprises the most active portions of the genome than heterochromatin. Over 92% of the human genome is occupied by euchromatin. It is found in both eukaryotic cells and prokaryotic cells.
Functions of Euchromatin:
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- Transcription can be easily initiated in the Euchromatin as it is more open to allow RNA polymerase complexes and gene regulatory proteins.
- Euchromatin participates in the active transcription of a segment of DNA into mRNA. If euchromatin is present in the gene it means the gene is actively transcribed.
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What is Heterochromatin?
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Heterochromatin is a tightly packed form of chromatin(DNA, RNA & protein) and it has a dense texture. Due to its condensed structure, it doesn’t allow the transcription of a segment of DNA into mRNA. It blocks DNA replication and transcription. Only less than 10% of genomes are occupied by heterochromatin.
There are two main types of heterochromatin, they are
- Constructive Heterochromatin
- Facultative Heterochromatin
Constructive Heterochromatin
It is a stable form of heterochromatin because it doesn’t loosen up to form the euchromatin. Constructive heterochromatin contains a sequence of DNA called satellite DNA. It is usually found in the telomeres and centromeres of chromosomes.
Facultative Heterochromatin
Facultative Heterochromatin is the opposite of constructive heterochromatin because it changes its structure depending on the cell cycle. It also has a sequence of DNA known as Line DNA. An example of facultative heterochromatin is inactivated female X chromosome.
Functions of Heterochromatin:
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- It regulates the genes and protects the chromosome integrity.
- Heterochromatin has a dense texture so it allows less DNA replication and Transcription.
Difference between Euchromatin and Heterochromatin
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| Comparison Parameters | Euchromatin | Heterochromatin |
|---|---|---|
| Definition | Euchromatin is a loosely packed Chromatin(DNA, RNA & protein) i.e. often transcriptionally active | Heterochromatin is a tightly packed chromatin(DNA, RNA & protein) i.e. transcriptionally inactive |
| Structure | Bead and string-like structure | Densely packed structure |
| Staining | It is less stained under stain nucleus | It is densely stained under stain nucleus |
| DNA Structure | In this, the DNA is loosely bounded | In this, the DNA is tightly bounded |
| Genes | In euchromatin, the genes are already active in transcription or will get ready for transcription | In heterochromatin, the genes are inactive for transcription |
| Transcription | Euchromatin is active for transcription | Heterochromatin is inactive for transcription |
| Folding | Euchromatin’s DNA is unfolded to form a bead-like structure | In Heterochromatin, the DNA is folded with the histone protein |
| DNA Quantity | It has less amount of DNA which is lightly compressed with histone protein | It has more amount of DNA which is tightly compressed with histone protein |
| Genome | It comprises more than 92% of the genome | It comprises less than 10% of the genome |
| Presence | Euchromatin is found in both eukaryotic cells and prokaryotic cells | Heterochromatin is only found in eukaryotic cells |
| Location | Euchromatin is located in the inner nucleus | Heterochromatin is located towards the periphery of the nucleus |
| Genetic variation | Euchromatin is affected by various genetic processes which result in variation in allele | Heterochromatin is not affected by any genetic process. No variation in allele |
| Functions | It allows the transcription of DNA with RNA and allows the variation within the genes | It replicates the DNA replication and transcription thus maintaining the strong structural integrity of the genome |
| Types | Only single euchromatin | There are two types of heterochromatin- Constructive heterochromatin and facultative heterochromatin |
| Speed of Replication | Euchromatin is early replicative than heterochromatin | Heterochromatin is late replicative than euchromatin |
| Examples | All chromatin in the genome except heterochromatin is an example of euchromatin | Telomeres, Centromeres and inactive female X chromosomes. |
Read More:
| Important Topics Related to the Chapter | ||
|---|---|---|
| DNA Genetic Material | Prokaryotic and Eukaryotic Transcription | Why is DNA negatively charged? |
| Biotechnology | DNA replication | Model Organism |
| DNA packaging | Translation | DNA Polymerases |
Things to Remember
- The chromosome in the cell consists of genetic material known as chromatin which is made up of DNA, RNA and proteins. It has two types, euchromatin and heterochromatin.
- Walther Flemming discovered chromatin in 1880. He founded the package of fibres in the cell nucleus and named it chromatin.
- Euchromatin is loosely packed chromatin which has less nucleus stain where heterochromatin are tightly packed chromatin which has a dense nucleus stain.
- The euchromatin is found in both eukaryote and prokaryote but heterochromatin is present only in a prokaryote.
- Euchromatin is a bead and string-like structure where heterochromatin has two types namely, line structure and satellite structure.
- The euchromatin allows transcription of a segment of DNA into mRNA where heterochromatin blocks DNA transcription.
- Over 92% of the genome is occupied by euchromatin whereas only less than 10% of the genome is occupied by heterochromatin.
- Euchromatin is present in the inner body of the nucleus where heterochromatin locates towards the peripheral of a nucleus.
- In genetics experiments, heterochromatin is more frequently located than euchromatin. This is because of the dense structure of heterochromatin.
Previous Year Questions
- A terminator codon which is called amber is… [COMEDK UGET 2011]
- Clover leaf model of tRNA was suggested by… [JKCET 2010]
- Histone octamer contains… [JKCET 2011]
- Heterogeneous nuclear RNA is converted to… [AMUEEE 2014]
- Who gave semi-conservative mode of DNA replication… [JKCET 2014]
- Adjacent nucleotides are joined by a… [AMUEEE 2015]
- The successive nucleotides of RNA are….[JIPMER 2001]
- When the centromere of a chromosome is located…
- The back bone of RNA consists of…
- When the centromere of a chromosome is…
- Purines found both in DNA and RNA...[NEET 2019]
- Ratio of complementary genes is… [NEET 2001]
- Which form of RNA has a structure resembling clover leaf… [NEET 2004]
- Which RNA is short lived… [COMEDK UGET 2006]
- Who discovered transduction in bacteria?… [COMEDK UGET 2011]
- VNTR stands for… [COMEDK UGET 2006]
- Human genome project was officially started in… [COMEDK UGET 2011]
- Franklin Conrat demonstrated that RNA is the genetic material of… [COMEDK UGET 2007]
- DNA replication is semi-conservative because... [COMEDK UGET 2008]
- DNA packaging in eukaryotes is done by formation of… [CUCET 2011]
Sample Questions
Ques: What are the similarities between euchromatin and heterochromatin? (1 Mark)
Ans: Both euchromatin and heterochromatin have DNA, RNA and protein and both have nucleosomes and DNA strands. The factor that differentiates them is the packaged density of Nucleosomes.
Ques: How euchromatin allows transcription of DNA? (1 Mark)
Ans: Euchromatin has an unfolded structure of nucleosomes and DNA string allows the gene regulatory proteins and RNA to combine with the segment of DNA which results in the transcription of DNA
Ques: What is the location of euchromatin and heterochromatin? (1 Mark)
Ans: Both chromatins are located inside the chromosomes, but euchromatin is located inside the inner body of the nucleus where heterochromatin is located towards the periphery of the nucleus.
Ques: Does X chromosomes of males can get inactive? (1 Mark)
Ans: The inactivation of the male X chromosome can occur often, but it is transient and confined to the last stage of spermatogenesis.
Ques: Differentiate Constructive and facultative heterochromatin. (2 Marks)
Ans:
| Constructive Heterochromatin | Facultative Heterochromatin |
|---|---|
| It is very stable and doesn’t allow the formation of euchromatin | It can change its structure depends on the cell cycle and sometimes result in the formation of euchromatin |
| It has structured DNA known as Satellite DNA | It also has structured DNA which is known as Line DNA |
Ques: State the difference between the structural genes in a transcription unit of prokaryotes and eukaryotes. (All India 2014, 2 Marks)
Ans: Prokaryotic structural genes are found in non-coding regions, while eukaryotic structural genes are divided into exons (coding DNA) and introns (non-coding DNA).
Ques: It is established that RNA is the first genetic material. Explain giving three reasons (Delhi 2012C, 3 Marks)
Ans: RNA is the first genetic material in cells because
(i) All the essential life processes are carried out around the RNA.
(ii) It is capable of both storing the genetic information and catalysing the chemical reactions.
(iii) It can do self-replication.
Ques: (i) What are the transcriptional products of RNA polymerase III?
(ii) Differentiate between ‘capping’ and ‘tailing’.
(iii) Expand mRNA. (All India 2014C, 3 Marks)
Ans: (i) tRNA, 55 rRNA and snRNAs (small nuclear RNAs) are the transcriptional product of RNA polymerase III.
(ii) In capping, an unusual nucleotide is added to 5′-end of hnRNA. In tailing, 200-300 adenylate residues are independentially added at 3′-end in a template. It is further known as mRNA
(iii) mRNA is heterogeneous nuclear RNA. It carries information related to genes to make protein. mRNA is also called messenger RNA.
Ques: Explain the location and role of the Promoter structural gene and terminator in a transcription unit. (All India 2014 C, 3 Marks)
Ans: The promoter and terminator usually define the end of the process of transcription. The promoter and terminator join the structural gene in a transcription unit. The promoter is located towards the structural gene and the terminator is located towards the coding strand.
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