Are chromosomal and plasmid DNA in the nucleoid?

Question

I know plasmid DNA is not part of the chromosome, according to my textbook, but can you still class it as being part of the nucleoid? Also is chromosomal DNA in the nucleoid?

Answer 1

"Nucleoid" (literally means nucleus-like), is a quite old term for "bacterial chromosome" (Better to write prokaryotic chromosome since in both type of prokaryotes i.e. Archaea (former archaebacteria) and bacteria (former eubacteria) the structure is similar).

Nucleoid structurally normally excludes the plasmid-DNA (the plasmid DNA is like additional or accessory). However sometimes a plasmid DNA could go through recombination with prokaryotic chromosome 's DNA (As seen in Hfr strain of Escherichia coli)

"Chromosome" in very brief means a structure made of DNA + Protein. In case of "bacterial-chromosome", it contains both DNA and Protein; and if you take away the protein from bacterial chromosome; what you get, is the chromosomal DNA.

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Reference:

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1. Microbiology / Pelczar, Chan and Noel/ Edition-5;
   • Part 2: Bactria,
     • Chapter 5 (Morphology and fine structure of bacteria)

"Because it is not discrete nucleus, this nebulous structure has been designated by such terms as the nucleoid , the chromatin body, the nuclear equivalent, even the bacterial chromosome"

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2. General Microbiology / Hans G. Schlegel / Edition-7:
   • Chapter-2 ; The cell and its structure:
     • 2.2 The prokaryotic cell (protocyte) -> 2.2.1: The bacterial 'nucleus'

" Plasmids : In addition to chromosomal DNA, many bacteria contain extrachromosomal DNA in closed, circular, double stranded form. These autonomously replicating DNA elements are called plasmids. Linear plasmids have been found in some bacteria"