Practice question

Genome size refers to total nucleotides in haploid set. Escherichia coli K-12 chromosome sequenced in 1997 measures about 4,641,652 base pairs, containing roughly 4,300 protein-coding genes, seven rRNA operons, and 86 tRNA genes. This 4.6 Mb circular molecule corresponds to about 1 mm contour length condensed 1000-fold into cell. Size varies among strains with prophages, insertion sequences, and pathogenicity islands, but 4.6 Mb serves as reference for transformation efficiency, plasmid copy control, and mapping distance. It approximates one picogram of DNA per million cells.