What is the Difference Between Plasmid DNA and Chromosomal DNA

The main difference between plasmid DNA and chromosomal DNA is that the plasmid DNA only contains additional genes not useful for the survival of the organism whereas chromosomal DNA contains all the necessary information for the growth, development, and reproduction of the organism. 

Plasmid DNA and chromosomal DNA are two types of DNA mainly found inside living cells. Both encode for the genes. Furthermore, plasmid DNA is a type of extrachromosomal DNA and is not a type of genomic DNA. In fact, only chromosomal DNA is considered as genomic DNA.

Key Areas Covered

1. What is Plasmid DNA
     – Definition, Structure, Role inside the Cell
2. What is Chromosomal DNA
     – Definition, Structure, Role inside the Cell
3. What are the Similarities Between Plasmid DNA and Chromosomal DNA
     – Outline of Common Features
4. What is the Difference Between Plasmid DNA and Chromosomal DNA
     – Comparison of Key Differences

Key Terms

Biological Information, Chromosomal DNA, Extrachromosomal DNA, Genomic DNA, Plasmid DNA

What is Plasmid DNA

Plasmid DNA is a type of DNA separated from the genomic DNA. Hence, it is a form of extrachromosomal DNA. It is always circular and naturally occurs inside prokaryotic cells. In addition, plasmid DNA is a small molecule when compared to chromosomes. A particular cell may contain a variable number of a particular type of plasmids. Generally, plasmid DNA is self-replicative DNA as it contains an origin of replication. Therefore, plasmids can replicate independently from the genomic DNA.

Figure 1: Plasmid DNA

Plasmid DNA encodes for several genes whose gene products are not necessary for the general functioning of the cell. These genes encode for antibiotic resistance, metal resistance, nitrogen fixation, and toxin production. This means the cell only requires these gene products for the survival under certain conditions. Both prokaryotic and eukaryotic cells uptake plasmid DNA naturally or under artificially-induced conditions. Therefore, the transformation of recombinant plasmids to a host organism can introduce new genes to the organism in a process called genetic engineering.

What is Chromosomal DNA

Chromosomal DNA is the genomic DNA. Both eukaryotic and the prokaryotic genome is organized into chromosomes. Prokaryotic genome only contains a single chromosome, which is circular. On the other hand, the eukaryotic genome contains several chromosomes, which are linear. Each chromosome contains an origin of replication and eukaryotic chromosomes contain more than one origin of replication due to their large size. Chromosomal DNA is always double-stranded.

Figure 2: Chromosomal DNA

The number of a particular type of chromosome in the genome depends on the type of species. However, most of the genomes on the earth are diploid and contain two copies of a particular type of chromosome. Since chromosomal DNA represents the genome of a particular organism, the information in the genes of the chromosomal DNA is necessary for the growth, development, and reproduction of the organism.

Similarities Between Plasmid DNA and Chromosomal DNA

• Plasmid DNA and chromosomal DNA are two types of DNA inside the cells.
• Generally, both are double-stranded.
• Also, both are circular in prokaryotes.
• Moreover, they encode for genes.
• Besides, both contain the origins of replication.

Difference Between Plasmid DNA and Chromosomal DNA

Definition

Plasmid DNA refers to a small, circular, double-stranded DNA molecule that is distinct from a cell’s chromosomal DNA while chromosomal DNA refers to a molecule that carries the genetic information in all cellular forms of life. Thus, this is the fundamental difference between plasmid DNA and chromosomal DNA.

Genomic DNA

Plasmid DNA is a form of extrachromosomal DNA and is not considered as genomic DNA while chromosomal DNA is a type of genomic DNA. This is a major difference between plasmid DNA and chromosomal DNA.

Occurrence

Another difference between plasmid DNA and chromosomal DNA is that the plasmid DNA naturally occurs only in prokaryotes while chromosomal DNA occurs in both eukaryotic and prokaryotic cells.

Size

Furthermore, the size attributes to another difference between plasmid DNA and chromosomal DNA. The size of the plasmid DNA can be 1-200 kbp while the chromosomes are typically larger than plasmid DNA.

Linear/Circular

Also, plasmid DNA is circular while chromosomal DNA in prokaryotes is linear and the chromosomal DNA in eukaryotes is circular.

Number

Moreover, the number of a particular type of plasmid DNA vary from 1 to thousand per cell while the number of copies of a particular chromosome per cell is determined based on the species.

Histone

Additionally, based on the association with histone, we can identify a difference between plasmid DNA and chromosomal DNA. That is; the plasmid DNA is not associated with histone proteins while chromosomal DNA in eukaryotes uses histone proteins for packing.

Type of Genes

Also, the genes in the plasmid DNA are not necessary for the general functioning of the cell while the information encoded by genes in the chromosomal DNA is necessary for the growth, development, and reproduction of the organism.

Replication

Replication is another difference between plasmid DNA and chromosomal DNA. Plasmid DNA can replicate independently from the genome while chromosomal DNA is replicated along with the genome.

Exons and Introns

Plasmid DNA has an open reading frame, but no exons or introns while chromosomal DNA of eukaryotes contains exons and introns, but in prokaryotes, there is only an open reading frame. Hence, this is also a difference between plasmid DNA and chromosomal DNA.

Transfer

Besides, plasmid DNA can be transferred by means of horizontal gene transfer while chromosomal DNA can only be transferred by means of cell division.

Importance

In addition, plasmid DNA plays a vital role in the recombinant DNA technology while chromosomal DNA is important in the study of genetic information.

Conclusion

Plasmid DNA is a type of extrachromosomal DNA and it is not a form of genomic DNA. It naturally occurs inside the prokaryotic cells. Moreover, it is a small, circular, double-stranded DNA molecule and the genes in it are not necessary for the general functioning of the cell. In contrast, chromosomal DNA is a type of circular or linear DNA, which belongs to the genome. Therefore, the information in the genes of chromosomal DNA is necessary for the growth, development, and reproduction of the organism. Thus, the main difference between plasmid DNA and chromosomal DNA is their structure and role inside the cell.

Reference:

1. “Plasmid / Plasmids.” Nature News, Nature Publishing Group, Available Here
2. “What Is a Chromosome? – Genetics Home Reference – NIH.” U.S. National Library of Medicine, National Institutes of Health, Available Here

Image Courtesy:

1. “Plasmid (english)” By User:Spaully on English wikipedia – Own work (CC BY-SA 2.5) via Commons Wikimedia 
2. “Chromosome en” By File:Chromosome-es.svg: KES47 (talk)derivative work: KES47 – File:Chromosome-es.svg (CC BY 3.0) via Commons Wikimedia