Term
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Definition
- The sequence of DNA bases is recorded as a sequence of complimentary bases in a single stranded mRNA molecule. - DNA-dependent RNA synthesis
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Term
| RNA Polymerase Overall Reaction: |
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Definition
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Term
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Definition
- Five core subunits:
- [image] α
- β
- β' (active site)
- ω
- σ
- No proofreading 3'-5' exonuclease
- Error rate of RNA synthesis: 1 error per 104 to 105 bases polymerized
- Synthesizes all three classes of RNA in E. coli.
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Term
| Template/Primer Requirements: |
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Definition
- No primer required to initiate RNA synthesis.
- DNA template required to determine identity of new nucleotides by Watson-Crick base pairing.
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Term
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Definition
- Initiation of RNA synthesis occurs at specific DNA sequences in the genome called promoters.
- Nt numbering: +1 is the first base pair to be copied into RNA.
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Term
| Promoter binding specificity (σ subunit): |
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Definition
- σ subunit determines sequenc-specificity of DNA binding.
- Several σ isoforms with differing sequence specificities and molecular weights.
- σ disociates from the core RNAP during elongation.
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Term
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Definition
- Determination of the +1 base
- Choice of template strand and overall direction of transcription.
- Control of frequency of transcription initiation: strong versus weak promoters.
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Term
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Definition
- Initiation
- Promoter binding by RNA polymerase (RNAP) to form closed complex.
- Open complex formation (local melting of dsDNA at the+1 position.)
- Initial RNA synthesis
- Elongation
- Termination
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Term
| E. coli transcription termination: |
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Definition
- ρ-dependent termination:
- The ρ RNA:DNA helicase disrupts the transcription bubble.
- ρ-independent termination:
- Structure of the RNA:DNA heteroduplex is less stable at certain sequences, which predisposes the transcription bubble to disassemble
- Self-complementary sequence in the transcript followed by a run of A/U base pairs, just prior to the 3' end of the transcript.
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Term
| DNA-dependent RNAP in Eukaryotes: |
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Definition
- RNAP I: pre-rRNAs
- RNAP II: mRNAs (primarily)
- Bind and transcribe from a variety of promoter sequences, which show a great range of promoter strength.
- RNAP III: tRNAs, 5S rRNA
- Certain portios of the promoter sequence are located within the coding sequence.
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Term
| Regulation of E. coli RNAP binding to promoters: |
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Definition
- Activator proteins:
- Facilitate RNAP binding to a specific promoter - increases the frequency of transcription initiation.
- e.g. cAMP-receptor protein (CRP)
- Repressor proteins:
- Block RNAP synthesis from specific promoters - reduce the frequency of transcription initiation.
- e.g. Lac repressor
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Term
| mRNA processing in eukaryotes: |
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Definition
- Synthesis of primary transcript in the nucleus.
- Synthesis of a "cap" at the 5' terminus
- Cleavage and poladenylation of 3' terminus
- Removal of introns by splicing
- Transport of processed (mature) mRNA to cytosol for translation into protein
- These events are catalyzed by large protein and protein/RNA complexes
- Eventual degradation.
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Term
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Definition
- Introns
- Internal sequences removed from the primary RNA transcript.
- Exons
- Sequences that are present in the primary RNA and in mature RNA
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Term
| Self-splicing RNAs (two groups): |
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Definition
- Gropu I:
- Mitochondrial, chloroplast and some nuclear rRNAs, tRNAs and some mRNAs
- Cofactor: Guanine nucleoside or nucleotide
- Group II:
- Mitochondrial and chloroplast mRNAs
- Cofactor: an adenylate residue within the intron sequence.
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Term
| Viral-encoded reverse transcriptase: |
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Definition
- Three enzymatic activities:
- Copies the viral RNA into an RNA:DNA heteroduplex (RNA-dependent DNA polymerase).
- Degrades the RNA half of the RNA:DNA duplex.
- Copies the DNA copy of the genome to make a dsDNA version of the viral genome (DNA-dependent DNA polymerase).
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Term
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Definition
- Cleaves polyproteins to generate the mature active proteins required for viral particle assembly andreplication
- The "protease inhibitors" used to treat HIV infections inhibit this enzyme and thus interrupt the viral replication cycle.
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