Final answer:
During the S phase of interphase, chromosomes are wrapped around proteins called histones, forming nucleosomes.
Step-by-step explanation:
During the S phase of interphase, each chromosome is wrapped around proteins called histones. Histones are evolutionarily conserved proteins that are rich in basic amino acids and form an octamer, around which DNA is tightly wrapped to form structures known as nucleosomes. These nucleosomes are then linked to each other with a linker DNA, further compacted into a 30 nm fiber, eventually forming metaphase chromosomes which are highly condensed and approximately 700 nm in width.