Question: 111: Read the following statements and choose the set of correct statements :
(a) Euchromatin is loosely packed chromatin
(b) Heterochromatin is transcriptionally active
(c) Histone octomer is wrapped by negatively charged DNA in nucleosome
(d) Histones are rich in lysine and arginine
(e) A typical nucleosome contains 400 bp of DNA helix
Choose the correct answer from the options given below :
(1) (b), (e) Only
(2) (a), (c), (e) Only
(3) (b), (d), (e) Only
(4) (a), (c), (d) Only
Answer: Option (4)
Explanation:
Euchromatin is lightly stained and loosely packed chromatin that is transcriptionally active,
so statement (a) is correct.
Heterochromatin is densely packed chromatin and is transcriptionally inactive,
hence statement (b) is incorrect.
A nucleosome consists of a histone octamer around which negatively charged DNA is wrapped due to electrostatic attraction, so statement (c) is correct.
Histones contain a high proportion of basic amino acids lysine and arginine,
which help them bind to negatively charged DNA, making statement (d) correct.
A typical nucleosome core particle contains about 146 base pairs of DNA,
not 400 base pairs, so statement (e) is incorrect.
Therefore, the correct set of statements is (a), (c), and (d),
corresponding to Option (4).