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Questions and Answers
What is the role of the 5’ cap added during RNA processing?
What is the role of the 5’ cap added during RNA processing?
Which component is primarily responsible for converting the primary transcript into mature mRNA?
Which component is primarily responsible for converting the primary transcript into mature mRNA?
What is included in the basal transcription complex formation?
What is included in the basal transcription complex formation?
What defines the regulatory regions of an mRNA-producing gene?
What defines the regulatory regions of an mRNA-producing gene?
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Which of the following best describes the primary transcript of RNA?
Which of the following best describes the primary transcript of RNA?
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What is the primary function of the promoter region in gene expression?
What is the primary function of the promoter region in gene expression?
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Which component of RNA carries genetic information from DNA for translation?
Which component of RNA carries genetic information from DNA for translation?
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What characterizes the non-coding regions of a gene?
What characterizes the non-coding regions of a gene?
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Which sequence is essential for the splicing of introns from the primary RNA transcript?
Which sequence is essential for the splicing of introns from the primary RNA transcript?
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What is the role of transcription factors in the transcription process?
What is the role of transcription factors in the transcription process?
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What happens to primary RNA transcripts during mRNA processing?
What happens to primary RNA transcripts during mRNA processing?
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How do untranslated regions (UTRs) affect mRNA?
How do untranslated regions (UTRs) affect mRNA?
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Where does RNA synthesis occur within the cell?
Where does RNA synthesis occur within the cell?
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Study Notes
Transcription Overview
- Transcription is the DNA-directed synthesis of RNA.
- It's the first step in gene expression, leading to protein synthesis.
- Each gene contains information specifying the final product and its regulated expression.
- To produce mRNA, the gene sequence and the exact start site are needed on DNA.
Structure of a Typical Eukaryotic Gene
- Composed of coding exons, non-coding introns, and non-coding consensus sequences (promoters).
- Promoters include the TATA box and CAAT box, serving as recognition sites for transcription factors.
- Splice acceptor and donor sequences are crucial for intron removal during RNA processing.
- Intron and exon numbers, sizes, and sequences differ between genes.
Promoters
- DNA sequences determining the RNA synthesis start site.
- A consensus sequence often includes "TATA" located within 15-30 base pairs upstream of the start site (TATA box).
- Other sequences required for promoter function include CAAT box and GC box.
- Transcription factors in eukaryotes bind to the TATA box, facilitating RNA polymerase attachment.
Splice Acceptor and Donor Sequences
- Consensus sequences found at the 5' and 3' ends of introns.
- Introns typically begin with GU and end with AG, preceding a pyrimidine-rich tract.
- Essential for splicing introns from the primary RNA transcript.
Features of Transcription
- Selective: Only specific parts of the genome are transcribed in a cell at a given time.
- Primary RNA transcripts undergo modification.
RNA Synthesis
- Occurs in the nucleus.
- Catalyzed by RNA polymerase.
- Protein-encoding genes generate mRNA as an intermediate.
- Regulatory mRNA sequences (UTRs) in the 5' and 3' untranslated regions affect process stability and translation efficiency but are not part of the final product.
- The initial mRNA is processed/edited.
RNA Polymerase, Transcription Initiation, and Regulatory Regions
- Eukaryotic cells contain multiple RNA polymerases.
- Proteins bind to the gene to be transcribed, initiating the process.
- Regulatory regions of the mRNA-producing gene include coding and regulatory regions.
- The regulatory regions are categorized into those ensuring basal and those regulating gene expression.
- Basal transcription complex formation requires several transcription factors.
- ssRNA is synthesized from dsDNA.
RNA Synthesis: Complementarity to DNA
- Newly synthesized RNA is complementary to the DNA template strand.
- The sequence of the template strand determines the sequence of the synthesized RNA.
Formation of the Transcription Complex
- RNA polymerase II assembly requires general and specific transcription factors.
- Enhancer sequences, coactivators, and TATA box elements contribute to the process.
RNA Processing
- Gene transcription produces larger RNA than mature mRNA.
- Primary transcripts include transcribed introns.
- Introns are removed, and exons are joined to form mature mRNA that's "capped and tailed."
- The 5' cap is a methyl guanosine residue added to protect mRNA from degradation and facilitate ribosome binding.
Addition of 5' Cap and Poly(A) Tail
- 5' cap: methylguanosine to prevent degradation and facilitate ribosome binding in protein synthesis.
- Poly(A) tail: a highly conserved AAUAAA sequence (polyadenylation signal) near the 3' end aids in mRNA stability and export.
Intron Removal
- Splice sites within genes delineate introns.
- The spliceosome removes introns and joins exons, forming mRNA.
- The spliceosome comprises the primary transcript, small nuclear RNAs (snRNAs), and snRNPs.
- Mature mRNA exits the nucleus through nuclear pores.
Alternative Splicing
- Genes can generate multiple proteins by joining different exon combinations of the primary transcript.
- Cell-specific regulation contributes to diverse protein production.
Inactivation of Prokaryotic RNA by Rifampin
- Rifampin inhibits prokaryotic RNA synthesis by binding to RNA polymerase and disrupting its conformation.
- Prokaryotic vs. eukaryotic RNA polymerase function differences are key.
Mutations in Splicing and Disease
- Mutations in splicing can lead to various diseases including thalassemias.
- Point mutations in TATA boxes, splice junctions, or intron-exon boundaries are potential contributors to thalassemias and other genetic diseases.
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