To avoid being degraded by nuclear exonucleases, nascent transcripts, pre-mRNA-processing intermediates, and mature mRNAs in the nucleus must have their ends protected. Which of the following mechanism are present in the cell to protect mRNA from degradation?

I. The 5′ cap is protected because it is bound by a heterodimeric nuclear cap-binding complex (CBC), which protects it from 5′ exonucleases and also functions in export of the mRNA to the cytoplasm.

II. 5’-5’ phosphodiester bond in the cap of mRNA plays crucial role in protection

III. The 3′ end of a nascent transcript lies within the RNA polymerase and is thus inaccessible to exonucleases 

#Question id: 2914

#Unit 2. Cellular Organization

The human genome is composed of many different types of DNA sequences, the majority of which do not encode proteins. Shown are the distribution and amount of each of the various types of sequences. Mark the correct options containing appropriate input for boxes A and B.

#Question id: 2915

#Unit 2. Cellular Organization

The structural maintenance of chromosome (SMC) proteins are extended proteins that form defined pairs by interacting through lengthy coiled-coil domains. Together with non-SMC proteins, they form multiprotein complexes that act to link two DNA helices together. Identify the SMC proteins in the figure given below and match them with their respective subunits.

i. Blue – Cohesin made up of Smc 1 and Smc 2 proteins.

ii. Green – Condensin made up of Smc 3 and Smc 4 proteins.

iii. Blue – Condensin made up of Smc 2 and Smc 4 proteins.

iv. Green – Cohesins made up of Smc 1 and Smc 3 proteins.

v. Blue – Condensin made up of Smc 1 and Smc 3 proteins.

vi. Green – Cohesins made up of Smc 2 and Smc 4 proteins.

#Question id: 2916

#Unit 2. Cellular Organization

Which of the following statement is INCORRECT regarding the packaging of DNA into higher order chromatin structure?

#Question id: 2917

#Unit 2. Cellular Organization

With respect to the interconversion between open and condensed chromatin shown below: Which of the directions (i) or (ii) would you anticipate would be the consequence of the following types of chromatin modification?

#Question id: 2918

#Unit 2. Cellular Organization

Some DNA sequences in our cells have high frequencies of methylated cytosines (hypermethylation); some others have a low frequency of methylated cytosines (hypomethylation). Which of the two methylation states best describes the kind of sequences listed below? 

 I. Satellite DNA in pericentromeric heterochromatin

II. Promoters 

III. Dispersed transposon repeats

IV. CpG islands 

V. Enhancers

#Question id: 2919

#Unit 2. Cellular Organization

Topoisomerases play the essential role of unlinking the DNA molecules to allow them to separate into the two daughter cells for cell division. Which of the following statements regarding the mechanism of topoisomerases is INCORRECT?