1. Transcription and RNA processing are energetically expensive processes for th
ID: 260937 • Letter: 1
Question
1. Transcription and RNA processing are energetically expensive processes for the eukaryotic cell. Suppose that initial transcript of a eukaryotic protein-encoding gene is 3000 nucleotides long before processing. Also assume that it contains several introns. Because the building blocks of RNA are all nucleoside triphosphates, then CTP, GTP, and UTP are all energetically equivalent to ATP. But on average the production of a translatable messenger RNA molecule will require much more than the 3000 ATP equivalents required for the addition of each ribonucleotide in the initial RNA transcript.
a. Briefly describe five different, specific processes that will require additional ATP equivalents (beyond the 3000) to create a functional messenger RNA molecule and export it from the nucleus.
b. The two transesterification reactions of RNA splicing do not themselves require an input of free energy to occur, yet RNA splicing by the spliceosome consumes a considerable amount of ATP. Why is ATP required for spliceosomal-mediated splicing?
Explanation / Answer
1. Processes where ATP equivalents are required:-
A.) ATP is required during assembly of RNA polymerase 2 pre initiation comolex- In the presence of ATP, TFIIH (a component of general transcription factor) phosphorylates Polymerase 2 to initiate transcription.
B.) GTP is required during 5' capping of mRNA, catalysed by RNA capping enzyme. - The final cap contains a 5' to 5' triphosphate linkage between the positively charged 7- methyl guanosine residue and the 5' end of RNA transcript.
C.)ATP is required during poly adenylation reaction, which is catalysed by poly A polymerase. It's a template independent RNA polymerase, which adds poly A, not specified by DNA. The substrate for this reaction is ATP.
D.) ATP is required during splicing. It's required for assembly of spliceosome complex and not for transesterification reactions.
E.) GTP is required during export of mature RNA from the nucleus.- RAN - GTP promotes the export of mature mRNA through the nuclear pore complex.
2.) After the loss of U4 from B2 complex. It's required that U2 at the brranch point interacts with U6 at the 5' splice site in the C complex, which would help in transesterification reaction to splice out introns. So, in order to form this particular structure, or to form this catalytic site, energy of ATP hydrolysis is required.
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