Introduction:
Chromosomes refer to a structure that consist genetic material and formed by DNA and protein. Chromosomes are coiled form of DNA that consist genes, nucleotides and regulatory components. Shape of chromosomes varies depending upon the species. In Prokaryotes, chromosomes are circular in shape and have one cell whereas in Eukaryotes, chromosomes are linear in shape. Bacteria’s falls in prokaryotes category hence have circular chromosomes. Virus is an agent responsible for causing deceases. Viral chromosomes consist of nucleic acid and protein. Nucleic acid could be either DNA or RNA; both do not exist together in viral chromosomes. Viral chromosomes can be either circular or linear in shape. Viruses do not have required enzymes, cell membrane, ribosome and capability of ATP synthesis hence they can not replicate independently in open environment, and they required a host cell for replication. Virus does not infect all cells of their hosts, they infect only specific cells of hosts. Bacteriophage is a species of virus that contaminate only bacteria.
Bacterial Chromosomes:
Bacterial chromosomes vary in size from 160,000 to 12,200,000 base pairs. Unlike eukaryotes chromosomes they do not have proper sequence in their structure and majority of bacterial chromosomes have one point for the initiation of replication. DNA of Bacterial chromosomes often formed a structure known as nucleoid. Nucleoid managed and maintained by histone proteins. The circular form of DNA helps chromosomes while replication and also provide stability.
Replication of Bacterial Chromosomes:
Replication process in bacteria complete in three major steps; first step is initiation, second is elongation and third is termination.
Initiation - During initiation phase the starting point of replication which is known as OriC and contain DNA structure, identified by protein DnaA. DnaA helps in regulating enzymes and other proteins which are required for chromosomes replication. DnaA with the help of histone-like protein released AT-region and unbind double-stranded DNA. It allows other DNA to enter into for replication. During this process DNA adenine methylase enzyme encourage stranded partition. Further DNA helicase and DnaB translocate replication fork and release parent DNA.
Elongation – After formation of replication fork they moved in a manner around circle so that a new structure like crossed circle formed. After this synthesis process begins. The leading strand and RNA primer synthesis start by primase enzyme. The synthesis starts at the place of origin of replication. After synthesis RNA primer get attached by DNA pol III and further add deoxyribonucleotides. After completion of synthesis process, DNA polymerase removes RNA primer and replaces it with DNA.
Termination – in termination process replication forks fused together and formed two separate DNA molecules. The terminus area on the chromosomes carries various terminator sites. A special protein on the terminator site stops replication process.
Viral Chromosomes:
Viruses are not living being hence they do not fall under prokaryotes or eukaryotes. Viral chromosomes contained DNA or RNA, protein and few genes. Bacteriophages chromosomes have double-stranded DNA with protein. Virus DNA gets into host body i.e. bacteria and integrate with the host chromosomes. Virus generally infects only those species of bacteria that can further transmit the disease to other cells even if they belong to different genera.
Replication of Viral Chromosomes:
Induction - Replication process in vial chromosomes start only after entering into host cells. When virus found and damaged cell of host, they enter into host cell. Viral chromosome then gets introduced and clubbed with bacterial chromosome. This process called induction.
Lytic Cycle – after induction process, replication process of viral chromosomes nucleic acid starts. Once the replication of nucleic acid completes, synthesis of protein took place. After protein synthesis all DNA part attached together and final leave the host cell.
References
Dorak, M. (2010, November 18). Viral and Bacterial Genetics. Retrieved January 7, 2012, from www.dorak.info: http://www.dorak.info/genetics/notes10.html
William S. Klug, Michael R. Cummings, Sarah M. Ward and Charlotte Spencer. (2009). Concepts of genetics. San Francisco: Pearson Benjamin Cummings.
