Molecular Basis of InheritanceEasy
Question
What are those structures that appear as ′bead-on-string′ in the chromosomes whenviewed under elctron microscope ?
Options
A.Nucleotide
B.Nucleosomes
C.Base pairs
D.Genes
Solution
Nucleosome is sub-microscopicsub unit of chromatin which is formed by wrapping ofDNA over a core of histone protiens. The term was coined by oudet et. al, (1975). It isoblate structure with a length og 10 nm and a thickness of 5-5.7 nm. Its core is callednu-body. THe latter is formed of fourpairs of histones molecules H2A, H2B, H3 and H2.DNA makes 1.75 turns over the octamer to from a nucleosome. Two adjacent nucleosomeare connected by a short segment of unbound DNA called linker DNA. A fifth type ofhistone called H1 is attached over the linker DNA. Nucleosome appear as ′bead-on-string′in the chromosomes under electron microscope.
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