Question

What is the primary mechanism of chromosome compaction in E. coli?

1) The chromosome is relaxed by reducing the amount of supercoiling, which decreases the overall size of the chromosome.
2) Histone proteins associate with the chromosome to form nucleosomes that efficiently compact the chromosome into the nucleoid.
3) The chromosome is packaged in a membrane-bound structure known as the nucleoid.
4) Proteins organize the chromosome into loops that are supercoiled to form the nucleoid.

Answer 1

In E. coli, chromosome compaction is primarily accomplished through supercoiling, with DNA being over-wound or under-wound and organized into looped domains that are coiled around basic proteins. The correct option is 1) The chromosome is relaxed by reducing the amount of supercoiling, which decreases the overall size of the chromosome.

Step-by-step explanation:

The primary mechanism of chromosome compaction in E. coli is not through the wrapping of DNA around histones to form nucleosomes as in eukaryotes, but rather through a process known as supercoiling. Supercoiling involves the DNA being either under-wound or over-wound from its normal relaxed state with the help of proteins and enzymes, such as DNA gyrase, which maintains this supercoiled structure.

Additionally, in E. coli, the circular chromosome is organized in a scaffold-like structure, which folds the chromosome into looped domains; these domains are further coiled around basic proteins, like Hu proteins. The correct option is 1) The chromosome is relaxed by reducing the amount of supercoiling, which decreases the overall size of the chromosome.