#Question id: 2907
#Unit 2. Cellular Organization
With respect to histone modifications, which, if any, of the following statements, is true?
#Question id: 2908
#Unit 2. Cellular Organization
The H3.H4 tetramers and H2A.H2B dimers each interact with a particular region of the DNA within the nucleosome. Which of the following statement is CORRECT regarding the characteristic binding of histones with the DNA?
I. Of the 147 bp of DNA included in the structure, the histone-fold regions of the H2A.H2B dimer interact with the central 60 bp.
II. Histone H3.H4 tetramers occupy a key position in the nucleosome by binding the middle and both ends of the DNA.
III. The amino-terminal region of H4 most proximal to the histone-fold region forms a fourth alpha helix that interacts with the final 13 bp at each end of the bound DNA.
IV. The H3.H4 tetramer associate with approximately 30 bp of DNA on either side of the central 60 bp of DNA bound by H2A.H2B dimer.
V. The two H2A.H2B dimers form the bottom part of the histone octamer located across the disc from the DNA ends.
#Question id: 2909
#Unit 2. Cellular Organization
The DNA can be labeled and used to probe a microarray, yielding a map of genomic sequences to which those particular nucleosomes bind. Because microarrays are often referred to as chips, this technique is called a ChIP-chip experiment. This experiment is designed to reveal the genomic DNA sequences to which a particular histone variant binds.
I. Chromatin is isolated from the cells and digested briefly with micrococcal nuclease (MNase).
II. A histone variant with an epitope tag is introduced into a particular cell type, where it is incorporated into nucleosomes.
III. The DNA bound by nucleosomes is protected from digestion, but the linker DNA is cleaved, releasing segments of DNA bound to one or two nucleosomes.
IV. The pattern of hybridization on the microarray reveals the DNA sequences bound by the nucleosomes with the histone variant.
V. Antibody is added, and the nucleosomes containing the epitope-tagged histone variant are selectively precipitated.
VI. The DNA in these nucleosomes is extracted from the precipitate, labeled, and used to probe a microarray representing all or part of the genomic sequences of that particular cell type.
Arrange the following statements in the correct order in which they are done.
#Question id: 2910
#Unit 2. Cellular Organization
With respect to the DNA methylation mechanism in mammalian cells, which of the following statements, if any, is true?
I. The principal role of the DNMT1 DNA methyltransferase is in de novo methylation.
II. The DNMT3A and DNMT3B DNA methyltransferases require hemi-methylated DNA as a substrate and are responsible for methylating nascent DNA strands that are complementary to methylated parental DNA strands.
III. Active DNA demethylation means removal of methyl groups from a hemi-methylated DNA double helix.
IV. DNA methylation is not essential in mammalian development.
#Question id: 2912
#Unit 2. Cellular Organization
HOTAIR is a lncRNA whose gene is found in the Hox C cluster in humans, but it acts by regulating expression of the Hox D genes on another chromosome (in trans) by recruiting to that locus Polycomb Repressive Complex 2. Which of the following statements is/are correct regarding this regulation?
#Question id: 2913
#Unit 2. Cellular Organization
Genome size (the length of DNA associated with one haploid complement of chromosomes) varies substantially between different organisms. Because more genes are required to direct the formation of more complex organisms, it is not surprising that genome size is roughly correlated with an organism’s apparent complexity. Which of the following statements is/are correct in reference to this rough correlation?
I. Many organisms of apparently similar complexities have very different genome sizes.
II. The number of genes, rather than genome size, is more closely related to organism complexity.
III. There is a roughly inverse correlation between organism complexity and gene density—the less complex the organism, the higher the gene density.
IV. Gene density in eukaryotic organisms is consistently higher and more variable than in their prokaryotic counterparts.