Plasmid vs Chromosome
Chromosomes and plasmids are components of a cell. Both chromosomes and plasmids carry genes, and they are made of DNA. Chromosomes are covered with protein, and they consist of linear DNA, but plasmids are circular and not covered with a protein.
Chromosomes are in nucleus and are observed clearly only in a nuclear division. Between the periods of nuclear divisions called interphase, arms of chromosomes are not clear, hence appears like a bundle of strings.
Chromosomes are made up of two strands of DNA and at one point they are attached somewhere along the chromosome, which is defined as centromere. These two DNA strands are called sister chromatids. Chromosomes are covered with proteins, and it carries genetic information from generation to generation.
Each species has a unique number of chromosomes in each cell and hundreds to thousands of genes. Their size is expressed in Mbp (Mega base pairs).
Plasmid is a small circular DNA found in all bacteria and some eukaryotes (Saccharomyces cerevisiae) . It is an extra DNA element except the genomic DNA or chromosomes. It has the self-replicating ability, and it possesses only a small number of genes. Plasmid size can vary from less than 1.0 kb to more than 200 kb , but the number of plasmid in a cell is a constant from generation to generation .
These are not essential for the function of the bacteria where they reside, but these genes give extra survival to bacteria. Some show resistance to antibiotic; i.e. some staphylococci possess penicillinase enzyme to break down penicillin. These staphylococci have plasmids consist of genes which code for penicillinase. Some plasmids are responsible for causing diseases. In Rhizobium leguminosarum, plasmid genes are responsible for the nitrogen fixation and nodule formation.
The number of molecules of a plasmid found in a single bacterial cell is called copy number. Copy number may ranges from 1 to 50, but this is specific for a given plasmid in host bacteria. Plasmid can be inserted to other bacteria, and it functions as a part of host bacteria. This ability is used in genetic engineering.
What is the difference between Chromosomes and Plasmid?
• Chromosome is covered with a protein whereas plasmid is not covered with protein.
• Chromosome is linear since it consists of linear DNA whereas plasmid is circular.
• Chromosomes are essential to cell function being the genetic information carrier, whereas plasmid are not essential to the function of bacteria where they reside, but these gens give extra survival to host bacteria.
• Chromosomes have several thousand genes, whereas plasmids have a small number of genes.
• Plasmid size can vary from less than 1.0 kb to more than 200 kb, whereas chromosome size is very much larger than a plasmid. For an example, size of a chromosome is expressed in Mega scale.
• Chromosomes have a centromere and two sister chromatids, whereas plasmid does not have chromatids or centromere.
• Plasmids are used as gene carriers to an alien cell; hence applied in genetic engineering, whereas chromosomes are not used as gene carriers.
Joshi, P, genetic engineering and its application