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Questions and Answers
What is the purpose of the 7-methylguanosine cap added to RNA?
What is the purpose of the 7-methylguanosine cap added to RNA?
- To aid in ribosome binding for translation
- To protect the RNA from degradation
- To facilitate the export of RNA from the nucleus
- All of these options (correct)
Which enzyme adds the poly(A) tail to the mRNA?
Which enzyme adds the poly(A) tail to the mRNA?
- Polyadenylate polymerase (correct)
- Spliceosome
- Endonuclease
- RNA Polymerase II
Where does the polyadenylation process occur in eukaryotic cells?
Where does the polyadenylation process occur in eukaryotic cells?
- Mitochondria
- Cytoplasm
- Nucleus (correct)
- Endoplasmic reticulum
What is removed during the splicing process of RNA?
What is removed during the splicing process of RNA?
Which polymerase is responsible for synthesizing mRNA in eukaryotes?
Which polymerase is responsible for synthesizing mRNA in eukaryotes?
What sequence do RNA polymerase II and endonuclease recognize for mRNA cleavage?
What sequence do RNA polymerase II and endonuclease recognize for mRNA cleavage?
What is the primary function of RNA Polymerase II?
What is the primary function of RNA Polymerase II?
Which transcription factor is thought to be involved in DNA melting?
Which transcription factor is thought to be involved in DNA melting?
What sequence is commonly found approximately -30 from the start site in RNA Pol II promoters?
What sequence is commonly found approximately -30 from the start site in RNA Pol II promoters?
Which protein specifically recognizes the TATA box?
Which protein specifically recognizes the TATA box?
During the transcription assembly process, which transcription factor binds to RNA Pol and targets it to the promoter?
During the transcription assembly process, which transcription factor binds to RNA Pol and targets it to the promoter?
What happens to RNA Pol II at the termination of transcription?
What happens to RNA Pol II at the termination of transcription?
Which factor unwinds DNA at the promoter during transcription initiation?
Which factor unwinds DNA at the promoter during transcription initiation?
What role does TFIIH play in the initiation of transcription besides unwinding DNA?
What role does TFIIH play in the initiation of transcription besides unwinding DNA?
What is the function of the 5' cap of mRNA?
What is the function of the 5' cap of mRNA?
What forms the 5' cap of eukaryotic mRNA?
What forms the 5' cap of eukaryotic mRNA?
Which sequences remain in mature mRNA after splicing?
Which sequences remain in mature mRNA after splicing?
What sequence is added at the 3' end of eukaryotic mRNA?
What sequence is added at the 3' end of eukaryotic mRNA?
Which enzymes are involved in capping the 5' end of mRNA?
Which enzymes are involved in capping the 5' end of mRNA?
What is the nature of introns?
What is the nature of introns?
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Study Notes
RNA Processing
- RNA processing involves three major modifications: addition of 7-methylguanosine caps to 5' termini, excision of non-coding intron sequences, and addition of poly(A) tails to 3' ends
- These modifications occur in the nucleus prior to transport to the cytoplasm
Eukaryotic RNA Polymerases
- Three different RNA polymerases are present in eukaryotes: RNA polymerase I, RNA polymerase II, and RNA polymerase III
- RNA polymerase I synthesizes pre-ribosomal RNA (precursor for 28S, 18S, and 5.8 rRNAs)
- RNA polymerase II is responsible for the synthesis of mRNA
- RNA polymerase III makes tRNAs and some small RNA products
Assembly of RNA Polymerase
- Assembly is initiated by interaction of TATA-binding protein (TBP) with the promoter
- Two transcription factors (TFIIA and TFIIB) bind to the promoter
- TFIIE and TFIIH bind to the promoter, where TFIIE is involved in DNA melting and TFIIH has helicase activity
RNA Polymerase II Promoters
- Conserved sequences include the TATA box and the Inr
- TATA box is located at -30 and has the sequence TATAAA
- Inr is located at +1 and has the sequence YYANTYY
RNA Strand Initiation and Promoter Clearance
- Kinase activity in TFIIH phosphorylates the polymerase, allowing it to escape the promoter
- Initially, 60-70 RNA nucleotides are synthesized
- Then, TFIIE and TFIIH are released, and the process moves to elongation
Elongation, Termination, and Release
- TFIIF remains attached to RNA Pol II
- Elongation factors help with efficiency
- E longation factors stop pausing and regulate post-transcriptional processing
- At termination, the phosphate is removed
Capping the 5' of mRNA
- Capping protects mRNA from 5' exonuclease degradation
- Cap is 7-methylguanosine linked to 5' end of mRNA
- Capping occurs early in transcription
Introns
- Introns are non-coding sequences located between coding sequences
- Introns are removed from the pre-mRNA and are not present in the mRNA
- Exons are composed of the sequences that remain in the mature mRNA after splicing
Polyadenylation
- A poly(A) tail is built at the 3' end of mRNA
- Poly(A) tail is synthesized by polyadenylate polymerase
- Poly(A) tail is a run of adenines at the 3' end of mRNA
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