BACTERIAL NUCLEOID

 NUCLEOID

—  The Nucleoid of a bacterial cell usually contains a single long, continuous, and frequently circularly arranged thread of Double stranded DNA called the Bacterial Chromosome.

—  The Nucleoid can be spherical, elongated, or dumbbell shaped.

—  Nucleoid carries all the genetic information required for the cell’s structures and functions.

—  Unlike the Chromosomes of Eukaryotic cells, Bacterial Chromosomes are not surrounded by a Nuclear envelope (membrane) and do not include histones.

—  The nucleoid can also be seen under a Light microscope by staining it with the Feulgen stain, which specifically stains DNA.

—  The DNA-intercalating stains DAPI (4′,6-diamidino-2-phenylindole) and Ethidium bromide are widely used for Fluorescence Microscopy of Nucleoids.

—  Experimental evidence suggests that the Nucleoid is largely composed of about 60 % DNA, plus a small amount of RNA (mRNA) and Protein (Transcription Factor Proteins) for regulating the bacterial genome.

—  Proteins helping to maintain the supercoiled structure of the Nucleic acid are known as “Nucleoid Proteins” or “Nucleoid-Associated Proteins” and are distinct from histones of eukaryotic nuclei.

—  The chromosome is attached to the plasma membrane. Proteins in the plasma membrane are believed to be responsible for

a)     Replication of the DNA

b)     Segregation of the new chromosomes to daughter cells during Cell division.

c)     DNA Recombination

d)     Gene expression