Statement: In the case of group II introns, the chemistry of splicing and the RNA intermediates produced are the same as those for nuclear pre-mRNA.

 Explanations: I. The intron uses an A residue within the branch site to attack the phosphodiester bond at the boundary between its 5’ end and the end of the 5’ exon-that is, at the 5’ splice site. This reaction produces the branched lariat.

II. A second reaction in which the newly freed 3’ -OH of the exon attacks the 3’splice site, releasing the intron as a lariat and fusing the 3’ and 5’ exons.

#Question id: 2895

#Unit 2. Cellular Organization

Match the following histone modifying enzymes with the respective functions they catalyze.

#Question id: 2896

#Unit 2. Cellular Organization

Different modification states of the residue Lys-9 on the tail of histone H3 could be interpreted to have different meanings. One example of how a histone modification can apparently influence a second modification present nearby is illustrated by the Drosophila HP1 protein. Which of the following statement is correct regarding this kind of epigenetic regulation?

#Question id: 2897

#Unit 2. Cellular Organization

The transcription of most protein coding genes in mammals (~70 percent) occurs at a lower rate than at TATA box–containing and initiator-containing promoters and begins at any of several alternative start sites within regions of about 100–1000 bp that have an unusually high frequency of CG sequences. Which one of the following best explains it?

#Question id: 2898

#Unit 2. Cellular Organization

The human genome is composed of many different types of DNA sequences, the majority of which do not encode proteins. From the following distribution and amount of each of the various types of sequences determine which of these is CORRECTLY expressed?

#Question id: 2899

#Unit 2. Cellular Organization

The H3.H4 tetramers and H2A.H2B dimers each interact with a particular region of the DNA within the nucleosome.

I. Histone H3.H4 tetramers occupy a key position in the nucleosome by binding the middle and both ends of the DNA.

II. The amino-terminal region of H3 most proximal to the histone-fold region forms a fourth a-helix that interacts with the final 13 bp at each end of the bound DNA.

III. The relatively short length of DNA bound by H2A.H2B dimers is sufficient to prepare the DNA for H3.H4 tetramer binding.

IV. The H3.H4 tetramer forms the bottom part of the histone octamer located across the disc from the DNA ends whereas two H2A.H2B dimer occupies the top part.

Which of the following represents the correct binding of the histones with the DNA?

#Question id: 2900

#Unit 2. Cellular Organization

Which of the following statement is INCORRECT from the set of statements given below?