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Cell Biology: Gene Expression and RNA Processing

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  • What is transcription?

    Transcription is the process of converting DNA into RNA using RNA polymerase enzymes.

  • What are the main types of RNA polymerase in eukaryotes and their products?

    RNA polymerase I produces rRNA, RNA polymerase II produces mRNA, and RNA polymerase III produces tRNA.

  • What is the difference between polycistronic and monocistronic mRNA?

    Polycistronic mRNA (prokaryotes) encodes multiple genes in one transcript; monocistronic mRNA (eukaryotes) encodes a single gene per transcript.

  • What is the role of a promoter in transcription?

    A promoter is a DNA sequence where RNA polymerase binds to initiate transcription, often containing elements like the TATA box.

  • What is the function of transcription factors in eukaryotic transcription?

    Transcription factors bind promoters and recruit RNA polymerase II to start transcription, forming the transcription initiation complex.

  • Describe the directionality of RNA synthesis during transcription.

    RNA polymerase synthesizes RNA in the 5’ to 3’ direction, reading the DNA template strand 3’ to 5’.

  • What happens during transcription termination?

    RNA polymerase stops at a terminator sequence; its tail phosphates are removed by phosphatases, allowing polymerase to dissociate and restart transcription.

  • What is a codon?

    A codon is a sequence of three nucleotides in mRNA that encodes a single amino acid or a start/stop signal.

  • What is the wobble hypothesis in tRNA function?

    The wobble hypothesis allows flexible base pairing at the third codon position, enabling one tRNA to recognize multiple codons.

  • What is the role of aminoacyl tRNA synthetase?

    Aminoacyl tRNA synthetase attaches the correct amino acid to its corresponding tRNA, charging the tRNA for translation.

  • What are the main rRNAs in prokaryotic and eukaryotic ribosomes?

    Prokaryotes: 16S (small subunit), 23S and 5S (large subunit). Eukaryotes: 18S (small), 5S, 5.8S, and 28S (large).

  • Where does RNA processing occur in eukaryotic cells?

    RNA processing occurs in the nucleus before mRNA is exported to the cytoplasm.

  • What is the purpose of the 5’ RNA cap?

    The 5’ cap is a methylated guanine added to protect mRNA from degradation and assist in translation initiation.

  • What is polyadenylation?

    Polyadenylation is the addition of a poly-A tail at the 3’ end of mRNA, enhancing stability and export.

  • What sequences signal RNA splicing sites?

    Splicing requires a 5’ splice site (usually GU), a 3’ splice site (usually AG), and a branch point sequence upstream of the 3’ site.

  • What is the spliceosome and its components?

    The spliceosome is a complex of snRNPs and proteins that removes introns from pre-mRNA during splicing.

  • What are the 7 steps of RNA splicing?

    Binding of U1 to 5’ site, U2 to branch point, spliceosome assembly, cleavage at 5’ site and lariat formation, cleavage at 3’ site, exon ligation, and exon junction complex recruitment.

  • What is alternative splicing?

    Alternative splicing produces different mRNA variants by combining exons in various ways, increasing protein diversity.

  • What is RNA editing?

    RNA editing alters nucleotide sequences in pre-mRNA, such as deamination converting cytosine to uridine or adenine to inosine.

  • What is the role of guide RNAs in RNA editing?

    Guide RNAs direct the insertion, deletion, or modification of nucleotides during RNA editing.