(d) Base pairs
[CBSE AIPMT 2011]
Correct Option (c)
Reason : Nucleosome appear as "beads-on-string" in the chromosones. Nucleosome is sub-microscopic sub-unit of chromatin which is formed by wrapping
of DNA over a core of histone proteins. The term was coined by Oudet, et. al (1975). It is oblate structure with a length of 10 nm and a thickness of 5-5.7 nm.
Its core is called nu-body. The latter is formed of four pairs of histone
molecules-H₂A, H₂B, H₃ and H₄. DNA makes 1.75 turns over the octamer to form a nucleosome.
Two adjacent nucleosomes are connected by a short segment of unbound DNA called linker DNA. A fifth type of histone called H₁ is attached over the linker DNA.