M2: DNA Transcription Flashcards
Process by which the information in a strand of DNA is copied into a new molecule of RNA
Transcription
Regulated process of DNA Transcription
- Protein-demand dependent
- Conservation of Cell Resources
- Enhanced Cell Fitness
Evidences of RNA as Intermediate Molecule in the Genetic Information Flow
- DNA does not participate in protein synthesis
- RNA is synthesized in nucleus or nuclear region
- RNA migrates to cytoplasm for protein synthesis
- RNA is chemically similar to DNA
DNA serving as a template for RNA Polymerase
DNA Template Strand
Similar 5’ to 3’ with transcribed RNA molecule
DNA Coding Strand
Initial step of Transcription
Template Binding
Recognized by sigma factors located upstream in the gene that signals the start of initial binding
Promoter
Cluster of gene found in bacteria that regulates genes
Operons
Similar sequences
- Different genes in the same organism
- One or more genes of related organisms
Promoters of Bacteria
Not similar promoter to Eukarya
Promoters of Archaea
Similar promoter to Eukarya
Recognition Sequences in Eukaryotic Promoter Region
- TATA - Goldberg-Hoyness Box
- CAAT/CCAAT box
- GC
Cis-Acting DNA Elements in Eukaryotes
- Core Promoter
- Proximal Promoter
- Enhancers and Silencers
Determines the binding site of RNAP II
Core Promoter
Helps modulate the level of transcription
Proximal Promoter
Cis-acting element that influence the efficiency or rate of transcription initiation by RNAP II
Enhancers and Silencers
Facilitates RNAP II binding and initiation of transcription
Trans-Acting Factors
Required trans-acting factor for RNAP II mediated transcription
General Transcription Factors
Trans-acting factor that influence the efficiency of RNAP II transcription initiation
Transcriptional activators and repressors
Catalyzed polymerization of RNA molecules, 5’ to 3’
RNA Polymerase
No. of RNA Polymerase in Eukaryotes
3
No. of RNA Polymerase in Bacteria
1
RNA Pol producing rRNA in nucleolus
RNA Pol I
RNA Pol producing mRNA in nucleoplasm
RNA Pol II
RNA Pol producing ssrRNA, tRNA in nucleoplasm
RNA Pol III
Provide the catalytic basis and active site of transcription in bacteria
RNA Polymerase Core Enzyme
Associated with dissociable subunit that recognizes specific promoters in bacteria
RNA Polymerase Holoenzyme
Recognizes the appropriate site on the DNA to initiate transcription
Sigma factor
Sigma factor recognizing promoter and initiation site
Promoter Reognition
Opens promoter complex
Local unwinding
RNA Pol starts to build a complimentary RNA strand
Chain initiation
Required in eukaryotes for initiation of transcription
Chromatin remodeling/Histone modification
RNA moves along 3’ to 5’
Chain Elongation
Site of adding nucleotides by RNA Pol in the RNA growing chain
3’ OH
Governed by specific base sequences on DNA
Chain Termination
Mechanisms of Termination in Bacteria
- Rho-dependent Termination
- Rho-independent Termination
Rho causes both the RNA and RNA Polymerase to be released from the DNA
Rho-dependent Termination
Rho-dependent termination site
Rho utilization/rut site
GC-rich sequences, containing an inverted repeat with a central non-repeating segment, followed by run of Adenines
Rho-independent Termination
Incorporation of polyadenylation sequence and cleavage of roughly 10-35 bases in 3’ direction
Termination in Eukaryotic Transcription
Incorporated sequence for eukaryotic transcription termination
Polyadenylation Signal Sequence
Initial or Primary transcripts of protein-coding mRNA
Eukaryotic Pre-mRNA
Post-Transcriptional Modifications in Eukaryotes
- Addition of 7-methylguanosine cap at 5’ end
- Poly A Tailing
- RNA Splicing
Protection from nuclease attack
Addition of 7-methylguanosine cap at 5’ end
Protects the mRNA
Poly-A Tailing
Removal of intervening sequence
RNA Splicing
Products of Transcription
mRNA, tRNA, & rRNA
Organism that have post-transcriptional mRNA
Eukaryote
Cistronicity of Prokaryotes
Polycistronic genes
Cistronicity of Eukaryotes
Monocistronic
Single gene, single transcription, single mRNA, but multiple and different proteins
Polycistronic genes