Final answer:
A single nucleosome is made up of eight histone molecules: two copies each of Histone H2A, H2B, H3, and H4, forming a structure around which DNA is tightly wrapped to facilitate compaction.
Step-by-step explanation:
A single nucleosome comprises eight histone molecules, with two copies each of Histone H2A, Histone H2B, Histone H3, and Histone H4. These histone proteins form an octamer around which approximately 146 base pairs of DNA wrap 1.65 times. The histone octamer consists of a (H3-H4)2 tetramer and two H2A-H2B dimers. The linkage of DNA to this octamer of histones and the alternating structure with linker DNA provides a first level of compaction of eukaryotic DNA. The nucleosomes are further compacted into a 30 nm fiber, significantly shortening the DNA molecule and contributing to the overall compaction necessary for fitting the large genomes of eukaryotes into the relatively small nuclear space.