A) Nucleotides
B) Nucleosomes
C) Base pairs
D) Genes
Correct Answer: B
Solution :
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-\[{{H}_{2}}A,\]\[{{H}_{2}}B,{{H}_{3}}\] and \[{{H}_{4}}\] 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 \[{{H}_{1}}\] is attached over the linker DNA. Nucleosomes appear as 'beads-on-string' in the chromosomes under electron microscope.
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