Chromosome of Cyanobacteria

The DNA in cyanobacteria is organized into a complex helical and folded structure and is distributed uniformly throughout the cytoplasm. It is likely that DNA is associated with histone like proteins and RNA. The size of the genome varies widely in cyanobacteria with molecular weight ranging between 1.6x109 and 8x109 daltons. Most of the unicellular cyanobacteria possess genomes of about 1.6x109 – 2.7x109 daltons. Filamentous cyano bacteria how ever have larger genomes.
Viral Genome
The core of the virion is made up of nucleic acid, either DNA or RNA never both. Four types of nucleic acid are formed in viruses with reference to number of strands. They formed in viruses with reference to number of strands.
They are:
1- Single stranded DNA ( ssDNA) Eg.Ø X 174
2- Double stranded DNA (dcDNA) Eg. Herpes virus
3- Single Stranded RNA (ssRNA) eg. TMV
4- Double stranded RNA (dsRNA) eg. Reovirus
The ssDNA may be linear (Parvovirus) or circular (Ø X 174). The ssDNA becomes double-stranded during replication when it is called replicative form (RF).
Double stranded DNA (dsDNA) is found in many animal viruses and bacteriophages. It maybe linear (in bacteriophages), cross-linked (Vaccinia virus) or closed circular duplex (Papova virus)
Single- stranded RNA (ssRNA) found in a variety of animal viruses and plant viruses maybe plus (infectious) RNA as in RNA bacteriophage, togaviruses etc or minus (non- infectious) as in rhabdoviruses and paramyxoviruses. Plus ssRNA directly acts as mRNA and is translated to proteins on host ribosomes where as minus ssRNA first transcribe in mRNA through an RNA/DNA intermediate and then gets translated to proteins.
Double- stranded RNA is found in animal viruses like reovirus.
In general, plant viruses have RNA (ss/ds) as genetic material except for canlimovirus and geminivirus which contain DNA. Animal viruses have DNA (ds) and RNA (ss/ds). Bacteriophages have DNA (ss/ds) or RNA (ss/ds). Most phages are DNA viruses.

Posted in: Microbiology