The letter a indicates globules containing eight subunits each. a filamentary structure forms two turns around each globule. letter a marks the filamentary structure between the globules. letter b marks one of the globules. letter c marks one subunit of the globule. the letter a indicates globules containing eight subunits each. a filamentary structure forms two turns around each globule. letter a marks the filamentary structure between the globules. letter b marks one of the globules. letter c marks one subunit of the globule. supercoils a nucleosome a dna double helix histones loops