This set of Molecular Biology Questions and Answers for Freshers focuses on “Genome Organization – 2”.
1. Histone H1 binds two DNA helices ____________
Explanation: Upon interacting with a nucleosome, H1 binds to the linker DNA at one end of the nucleosome and the central DNA helix of the nucleosome bound DNA. This protects the ≈20 base pair linker DNA from nuclease digestion.
2. The distinct zig – zag appearance of the chromatin fibre is due to ____________
b) Histone H1
c) Histone core
d) Linker DNA
Explanation: Histone H1 binding produces a more defined angle of DNA entry and exit from the nucleosome. This effect results in the nucleosomal DNA taking on a distinct zig – zag appearance.
3. With respect to Histone H1 DNA packaging which of the following is false?
a) H1 induce 10 nm fibre formation
b) H1 binding gives nucleosome a defined angle
c) H1 stabilizes higher order chromatin structures
d) H1 binds to two DNA helices at once
Explanation: As the salt concentration increases in a test tube, addition of H1 results in the nucleosomal DNA forming a 30 nm fibre. This structure formed in vivo is known to be the next level of DNA compaction.
4. With respect to the solenoid model of nucleosome, which of the following is true?
a) Helical model
b) 8 nucleosomes per turn
c) Structure supported by X – ray diffraction
d) Helical pitch of approximately 13 nm
Explanation: The solenoid model of nucleosomal DNA packaging is supported by both EM and X – ray diffraction studies. This study indicated that the 30 nm fibre is composed of nucleosome stacked on edge in the form of a helix.
5. What marks the difference between the solenoid and the zig – zag models of 30 nm fibres?
a) Linker histone molecule
b) Linker DNA
c) Nucleosome structure
d) 10 nm fibre
Explanation: Unlike the solenoid model, the zig – zag conformation requires the linker DNA to pass through the central axis of the fibre in a relatively straight form. Thus, longer linker DNA favors this conformation. Because the average linker DNA varies between species, the form of the 30 nm fibre may not always be the same.
6. The histone tails stabilizes the 30 nm fibre by interacting with adjacent nucleosomes __________
Explanation: Core histones lacking their N – terminal tails are incapable of forming the 30 nm fibre. The tails is to stabilize the 30 nm fibre by interacting with adjacent nucleosomes. This model is supported by the three dimensional structure of the nucleosome., which shows that the amino terminal tails of H2A, H3 and H4 each interact with adjacent nucleosomes in the crystal lattice.
7. Which of the following is not a characteristic of nuclear scaffold?
a) Associated with loops of 40 – 90 kb
b) Topoisomerase I
c) SMC protein
d) Proteinacious in nature
Explanation: Two classes of protein contributing to nuclear scaffold have been identified, that are, topoisomerase II and SMC protein. Presence of Topo II as a protein associated with the structure can be proved when the cells are treated with drugs which results in DNA breaks at the sites of Topo II DNA bindings. The treatment generates DNA fragments of about 50 kb size.
8. Which histone molecule produces novel binding sites for protein components of the kinetochore?
a) CENP – A
Explanation: A histone variant CENP – A, is associated with the nucleosome that include centromeric DNA. In this region CENP – A replaces H3 subunit in the nucleosomes. These nucleosomes are incorporated into the kinetochore which mediates attachment of the chromosome to the mitotic spindle. The extended tail of CENP – A may generate these novel binding sites for other binding protein components of the kinetochore.
9. With respect to remodeling complex of nucleosome, which of the following is not true?
a) Does not require ATP
b) Favors sliding of histone
c) Favors transfer of histone
d) Favors remodeling of histone
Explanation: The stability of the DNA-histone core interaction is influenced by large protein complexes referred to as nucleosome remodeling complexes. These multi – protein complexes facilitate changes in the nucleosome location or interaction with the DNA using the energy of ATP hydrolysis.
10. Positioning of nucleosome is beneficial ___________
Explanation: Due to dynamic interactions with DNA, most nucleosomes are not fixed in their locations. But there are occasions when restricting nucleosome location, called positioning, can be beneficial. Positioning allows DNA binding site to remain as accessible linker DNA region for regulatory proteins.
Sanfoundry Global Education & Learning Series – Molecular Biology.
To practice all areas of Molecular Biology for Freshers, here is complete set of 1000+ Multiple Choice Questions and Answers.