Transcription in Eukaryotes/RNA Modification (I) Flashcards
How many RNA pols are in eukaryotic cells?
There are three different RNA pols
I, II, and III
How many RNA pols are in bacterial cells?
There is only one RNA pol in bacterial cells
What does RNA pol I transcribe?
Most genes that encode rRNAs
What does RNA pol II transcribe?
All genes that encode mRNAs
Some genes that encode snRNAs
What does RNA pol III transcribe?
All genes that encode tRNAs
All genes that encode 5S rRNA (?)
Some genes that encode snRNAs
When do eukaryotic RNA pols terminate transcription?
When they encounter terminators at the end of a region
What are the similarities between E. coli RNA pol-transcribed genes and eukaryotic RNA pol I or III-transcribed genes?
They both have an A—T rich region that destabilizes base pairing between the RNA and template strands in the open complex
The process of termination for RNA pol I-transcribes genes is similar to what?
Rho-dependent termination in E. coli; proteins other than RNA pol I are required for termination
Termination of RNA pol III-transcribed genes is similar to what?
Rho-independent termination; other proteins are not required for termination
What is the terminator for RNA pol II-transcribed genes called?
The polyadenylation signal sequence
The polyA signal sequence
What is termination coupled to? (?)
A specific modification to the RNA that occurs after transcription
What happens to RNAs in eukaryotic cells after transcription?
RNAs often undergo several modifications after transcription
Where does RNA modification occur?
In the nucleus, before a mRNA is translated and before noncoding RNAs achieve their final form
What are some important RNA modifications?
Processing
Splicing
Base modification
5’ capping
3’ polyadenylation
What occurs during processing?
Portions of a single transcript are removed to create one or more functional products
What is a common modification to rRNAs and tRNAs?
Processing
What is an example of processing in rRNA ?
A single large RNA is transcribed from a rRNA gene. Once the transcript has been produced, portions of the RNA are removed, making three smaller transcripts.
The smaller transcripts are the final functional products of the gene
What is an example of processing in tRNA?
A single large RNA is transcribed from the tRNA gene. Portions of the transcript are enzymatically removed to create one smaller final product
What is splicing?
The removal of introns from a transcript
What are introns?
Non-coding sequences within a transcript that lie between coding sequences (exons)
How does splicing work?
Introns are removed and exons are joined together to create one uninterrupted coding sequence
Which RNA participates in the process of splicing?
snRNA
What is a common modification to mRNAs and some rRNAs and tRNAs?
Splicing
What is splicing similar to?
The removal of introns from a transcript
What is base modification?
The chemical alteration of bases within a transcript
What modification very commonly occurs in tRNAs?
Base modification
What modification very commonly occurs to mRNAs?
Capping and polyA tailing
What is capping?
The addition of 7-methylguanosine monophosphate to the 5’ end of an mRNA
What is the importance of capping?
It is needed for exon splicing, the transport of the RNA from the nucleus to the cytoplasm, and for the attachment of the ribosome to the RNA at the start of translation
What is polyadenylation/polyA tailing?
The addition of multiple adenosine monophosphates to the 3’ end of a transcript
The number of nucleotides varies from a few dozen to several hundred
What does polyA tailing do to RNA?
It helps stabilize the RNA and prevents it from being degraded
It is necessary for the translation of the RNA
