The main difference between linear and circular DNA is that linear DNA consists of two ends in each side, whereas circular DNA does not have an end. Furthermore, the genetic material in the nucleus of eukaryotes is linear DNA while the genetic material of prokaryotes, as well as mtDNA and cpDNA, are circular DNA. In addition to these, in plasmids, some DNA is linear while supercoiled plasmid DNA is circular.
Linear and circular DNA are two structures of DNA. Generally, DNA is the type of nucleic acid that stores genetic information of both eukaryotes and prokaryotes.
Key Areas Covered
1. What is Linear DNA
– Definition, Structure, Occurrence
2. What is Circular DNA
– Definition, Structure, Occurrence
3. What are the Similarities Between Linear and Circular DNA
– Outline of Common Features
4. What is the Difference Between Linear and Circular DNA
– Comparison of Key Differences
Key Terms
Circular DNA, Eukaryotes, Linear DNA, Prokaryotes, Telomeres
What is Linear DNA
Linear DNA is the DNA with two ends on each side of the DNA molecule. Generally, this type of DNA occurs in the form of eukaryotic chromosomes. They occur inside the nucleus. One of the main characteristic features of eukaryotic DNA is their large size. Generally, eukaryotes are complex organisms when compared to prokaryotes. Therefore, their genomes are also large. For example, the size of the human genome is 2.9 billion base pairs. Moreover, this DNA is arranged into 23 homologous pairs of chromosomes. Thus, linear DNA in the chromosomes of eukaryotes has to undergo tight coiling and dense packing.
Figure 1: Eukaryotic Chromosomes
Furthermore, the presence of linear chromosomes makes it easy to undergo transcription of large genomes. It is because of the difficulty to unwind large circular chromosomes due to torsion strain. However, the major disadvantage of the presence of large linear DNA is telomeres or terminal ends, which are unstable and more prone to become mutated. In addition to these, the ends of the linear chromosomes do not undergo complete replication, leading to the loss of DNA from ends. However, linear chromosomes can convert into circular DNA by removing all telomeric ends.
What is Circular DNA
Circular DNA is the type of DNA with no ends. Basically, the genome of the prokaryotes is a single chromosome, which is a covalently closed circular DNA molecule. In contrast to eukaryotic chromosomes, genome or the single chromosome of prokaryotes is small in size. In bacteria, the size of the genome is around 10 million base pairs. Due to their small size, prokaryotic chromosomes do not undergo packing. Although they are circular, due to their small size, prokaryotic chromosomes can undergo transcription easily. In addition to these, prokaryotic chromosomes do not undergo end replication problem due to their circular shape.
Figure 2: Circular DNA
1. Chromosome, 2. Plasmids
Moreover, the same as linear DNA conversion into circular DNA, circular DNA itself can undergo linearization. However, prokaryotes with the conversion of circular DNA into linear DNA are still viable. Significantly, prokaryotes such as Borrelia burgdorferi have linear chromosomes. Both mitochondrial and chloroplast DNA are single circular molecules. Generally, the genes in both genomes mainly encode for enzymes. In contrast, plasmids are another type of circular DNA, which mainly occurs in the cytoplasm of prokaryotes. During gel electrophoresis, they occur in three forms: supercoiled, which is circular, open-circular, and linear.
Similarities Between Linear and Circular DNA
- Linear and circular DNA are two structures of DNA.
- They are made up of DNA nucleotides.
- The main function of both types of DNA is to store genetic information while undergoing transcription and translation to produce their gene products.
- Plasmids can occur in both linear and circular types.
Difference Between Linear and Circular DNA
Definition
Linear DNA refers to the DNA with two ends while circular DNA refers to the DNA with no ends.
Examples
The genetic material in the nucleus of eukaryotes is linear DNA while the genetic material of prokaryotes, as well as mtDNA and cpDNA, are circular DNA.
Occurrence
Linear DNA exclusively occurs inside the nucleus while circular DNA occurs in the cytoplasm or inside organelles.
Size of DNA
Generally, linear DNA is large in size while circular DNA is small in size.
Organization
Furthermore, linear DNA undergoes tight coiling and dense packing inside the nucleus while circular DNA does not undergo packing.
Ease of Transcription
Linear DNA is easy to transcribe while large circular DNA is difficult to transcribe due to the torsion strain that occurs during DNA unwinding.
Presence of Telomeres
While linear DNA contains telomeres, circular DNA does not contain telomeres.
End Replication Problem
Moreover, linear DNA has to face end replication problem while circular DNA does not undergo the end replication problem.
In Plasmids
In plasmids, some DNA is linear while supercoiled plasmid DNA is circular.
Conclusion
Linear DNA is a DNA structure with two ends. Generally, eukaryotic chromosomes are linear. Moreover, they consist of a large number of base pairs. On the other hand, circular DNA is the DNA with no ends. Prokaryotic chromosomes are circular while both mitochondrial and chloroplast DNAs are circular as well. However, circular DNA is small in size. Therefore, the main difference between linear and circular DNA is the structure of DNA.
References:
1. “Linear Chromosome.” Wikipedia, Wikimedia Foundation, 17 June 2019, Available Here.
2. “Circular DNA.” Circular DNA – an Overview | ScienceDirect Topics, Elsevier B.V., Available Here.
3. “Agarose Gel Electrophoresis.” Electrophoresis, Available Here.
Image Courtesy:
1. “Chromosome” By File:Chromosome-upright.png (CC BY-SA 3.0) via Commons Wikimedia
2. “Plasmid (english)” By User:Spaully on English wikipedia – Own work (CC BY-SA 2.5) via Commons Wikimedia
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