Final answer:
The nucleosome assembly begins with H3-H4 histone dimers forming a tetramer, which associates with two H2A-H2B dimers to form the octameric core that DNA wraps around to create the nucleosome structure.
Step-by-step explanation:
Assembly of the Nucleosome Core Particle
The correct answer to the question of how a nucleosome is assembled is option b. In assembling a nucleosome, normally the H3-H4 histone dimers first combine to form a tetramer, which then further combines with two H2A-H2B histone dimers to form the octamer. This octamer forms the core around which DNA wraps to form the nucleosome complex. The H1 histone, often referred to as the linker histone, is not part of this core structure but instead binds the entry and exit points of the DNA, stabilizing the structure.
The nucleosome is the fundamental subunit of chromatin and the first level of DNA compaction. It consists of a segment of DNA wound in sequence around eight histone protein cores. This structural unit looks like beads on a string under an electron microscope, with the 'beads' being the nucleosome complexes and the 'string' being the linker DNA.