Arrange the given structures involved in packaging of DNA Helix.
(A) Chromatin
(B) Chromatin fibers
(C) Nucleosome
(D) Euchromatin
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (C), (A), (B), (D)
(C) Nucleosome — first. The negatively charged DNA is wrapped around a unit of eight positively charged histone molecules, the histone octamer. This first unit of packaging is the nucleosome. One nucleosome holds about 200 bp of DNA.
(A) Chromatin — second. Nucleosomes are the repeating units of chromatin, the thread-like stained bodies of the nucleus. Under the electron microscope chromatin looks like ‘beads-on-string’, the beads being the nucleosomes.
(B) Chromatin fibers — third. The beads-on-string structure is packaged further into chromatin fibers. At metaphase these fibers coil and condense to form chromosomes.
(D) Euchromatin — last. The packed chromatin of the nucleus is not packed to the same degree everywhere. The loosely packed, lightly stained regions are euchromatin, and the densely packed, dark regions are heterochromatin. Euchromatin is transcriptionally active, that is, its genes are being read.