Final answer:
Nucleosomes form when DNA wraps approximately 1.7 times around the histone octamer in a left-handed coil. This contributes to the high degree of compaction needed for DNA packaging within the eukaryotic cell nucleus.
Step-by-step explanation:
Nucleosomes are formed when DNA wraps around 1.7 times around the histone octamer in a left-handed coil. The correct option for this statement is (b). In this process, the eukaryotic human cell DNA, which is about 2 meters long, is tightly packed within a cell that has a diameter of 5-10 micrometres. This tightly wrapped DNA around the histone octamer is essential for the higher-order compaction of DNA, allowing it to fit neatly within the confines of the cell nucleus. Each nucleosome contains eight histone proteins, which include two copies each of H2A, H2B, H3, and H4. This structure winds 146 base pairs of DNA and is linked to the next nucleosome via linker DNA of 54 base pairs that is associated with a single H1 histone molecule. This organization results in a 'beads on a string' appearance under an electron microscope. The tightly wound nucleosomes are further coiled into a structure called the 30 nm fiber and eventually give rise to the metaphase chromosome structure during cell division.