DNA and Chromosomes

DNA and Chromosomes

Bacteria do possess a typical single circular chromosome comprising of a single circular molecule of DNA having associated proteins. It has been duly observed that the chromosome is duly looped, folded, and linked at one or several points to the respective plasma membrane. In reality, the DNA of E. coli*, has approximately four million base pairs, nearly 1 mm in length, and almost 1000 times larger than the entire cell. It may be observed that the DNA is rather quite thin, and is closely packed inside the cell, thereby this apparently twisted and adequately coiled macromolecule conveniently takes up merely 10% of the entire cell’s volume.

Eukaryotic chromosome’s DNA is generally found to be more tightly condensed (i.e., coiled) in comparison to the prokaryotic DNA.

The following Table 6.1 records the comparison between the eukaryotic and the prokaryotic chromosomes :

Table 6.1. Comparison Between Eukaryotic and Prokaryotic Chromosomes

The latest developments in genetic research has revealed that an extensive and intensive clear cut understanding of the chromosomal structure, besides the mechanism which enables the cell to afford turning of genes on and off to yield urgently required ‘crucial proteins’ when needed. Interestingly, the aforesaid modulation of gene expression meticulously governs the following two vital operations in a living system, such as :

(a) differentiation of the eukaryotic cells right into the various kinds of cells usually observed in the multicellular organisms, and

(b) on going critical and specific activities in an ‘individual cell’.