Question

Given below are five groups of five terms each. Arrange the terms in each group in proper sequence:

i) DNA, Chromatin, Chromosomes, Nucleosome, Histone

Answer 1

Answer:

The prokaryotes (Greek for 'before nucleus' - including Eubacteria and Archaea) lack a discrete nucleus, and the chromosomes of prokaryotic cells are not enclosed by a separate membrane.

Most bacteria contain a single, circular chromosome. (There are exceptions: some bacteria - for example, the genus Streptomyces - possess linear chromosomes, and Vibrio cholerae, the causative agent of cholera, has two circular chromosomes.) The chromosome - together with ribosomes and proteins associated with gene expression - is located in a region of the cell cytoplasm known as the nucleoid.

The genomes of prokaryotes are compact compared with those of eukaryotes, as they lack introns, and the genes tend to be expressed in groups known as operons. The circular chromosome of the bacterium Escherichia coli consists of a DNA molecule approximately 4.6 million nucleotides long.

In addition to the main chromosome, bacteria are also characterised by the presence of extra-chromosomal genetic elements called plasmids. These relatively small circular DNA molecules usually contain genes that are not essential to growth or reproduction.