RNA Processing MCQ - Practice Questions & Answers

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Transcription in Eukaryotes & RNA Processing

RNA polymerase in eukaryotes requires the assistance from additional proteins called transcription factors, that first bind to the promoter region and then recruit the RNA polymerase.
The eukaryotes have three polymerases that are each made up of 10 subunits or more.
In eukaryotes, the monocistronic structural genes have interrupted coding sequences – the genes in eukaryotes are split.
The coding sequences or expressed sequences are defined as exons.
Exons are said to be those sequences that appear in mature or processed RNA.
The exons are interrupted by introns.
Introns or intervening sequences do not appear in mature or processed RNA.
Therefore, the primary transcript of RNA contains both the exons and the introns and are non-functional.
Hence, it is subjected to a process called splicing where the introns are removed and exons are joined in a defined order.
The splicing of pre-mRNAs is conducted by complexes of proteins and RNA molecules called spliceosomes.
5' Capping:
- While the pre-mRNA is still being synthesized, a 7-methylguanosine cap is added to the 5' end of the growing transcript by a phosphate linkage.
- This moiety (functional group) protects the nascent mRNA from degradation.
- In addition, factors involved in protein synthesis recognize the cap to help initiate translation by ribosomes.
3' Poly-A Tail:
- An enzyme called poly-A polymerase then adds a string of approximately 200 A residues, called the poly-A tail.
- This modification further protects the pre-mRNA from degradation and signals the export of the cellular factors that the transcript needs to the cytoplasm.