Transcription
What two modifications are meant to protect the mRNA? Why does the mRNA need to be protected?
-Addition of the 5' methyl- G cap and addition of the 3' poly-A tail by poly-A polymerase -The mRNA needs to be protected from degradation (breaking down)
What is transcription dependent on?
cis- and trans- acting factors
What's an enhancer?
cis-element that helps aggregate transcription factors at the promoter
Where is the ending point of transcription?
it is designated by a termination signal
What is transcription?
The process of making RNA from DNA
What are ribonucleicproteins?
small nuclear ribonuclear proteins (snRNPs) [there's 5]
What is a sigma factor?
-responsible for promoter recognition (initiation or transcription) -recruits RNA polymerase to transcriptional start site
What is agarose gel electrophoresis?
-separates DNA molecules based on sizing (look at picture) -used for analyzing nucleic acids
What is transcription elongation?
-sigma factor dissociates from the RNA polymerase to allow for RNA synthesis to occur -synthesis of RNA 5' to 3' fashion -resulting RNA is complementary to the DNA sequence template strand
What does RNA polymerase do in transcription?
-synthesizes a complementary RNA copy from one of the DNA strands 3'-5' template strand of DNA is read by the polymerase
What are exons and introns?
-Exons are regions of the DNA molecule that code for specific RNAs. -lntrons are regions of the DNA molecule, between exons, that do not code for RNAs (aren't expressed in. "INtrons INterfere"
What is transcription termination?
-RNA polymerase traverses entire gene until a termination nucleotide sequence is encountered
What is a promoter?
-The region of mRNA where RNA polymerase binds and starts transcription -upstream of gene -cis-elements that are bound by sigma factors
What is transcription initiation?
-Transcription Start Site (TSS) -DNA double helix is denatured: unwound to make template strand accessible for RNA polymerase -Interaction of promoters and RNA polymerase regulates efficiency of transcription
What's a promoter?
-a cite where RNA polymerase can bind to begin transcription -includes cis-element consensus sequences
What is nucleic acid synthesis in prokaryotes?
-done 5' to 3' -equals 1 RNA polymerase (holoenzyme) 1. polymerase--> can't bind any specific DNA sequence 2. sigma factor
What special modifications do eukaryotic mRNAs require to become mature mRNA?
1. Addition of 5' cap (7-meG cap/7-methyl-guanasine) 2. Cleavage of 3' end and addition of 3' tail (3' poly-A tail) 3. Excision of introns--> splicing and ligate exons together (LOOK AT PICTURES)
What happens in eukaryotic transcription?
1. Occurs within nucleus 2. Euchromatin state is required to make DNA accessible to transcription factors and RNA polymerase 3. There are 3 RNA polymerase to transcribe different RNAs 4. RNA polymerases rely more heavily on transcription factors (TFs) 5. mRNA must leave nucleus for translation 6. Post-transcriptional processing if the newly synthesized mRNA is required to form a mature mRNA ready for translation
What do e.coli promoters have?
2 consensus sequences recognized by sigma factor
How many forms of RNA polymerases do eukaryotes possess? What does each one do?
3 forms Each one transcribes different types of RNA
How is the template strand read?
3' to 5'
What direction does transcription synthesis in?
5' to 3'
What product does RNA polymerase III make?
5s rRNA, tRNA
What are cis elements?
DNA sequence recognized by particular proteins
How does the sigma factor of prokaryotic RNA polymerase participate in initiation and elongation?
In initiation: is responsible for promoter recognition and enables specific binding of RNA polymerase to gene promoters and can place the enzyme in a position to initiate transcription In elongation: dissociates from the RNA polymerase to allow for RNA synthesis to occur
What is the main enzyme in transcription?
RNA polymerase
What is splicing?
Removing introns from RNA and sealing exons together
What is the -10 site called on the promoter region of DNA?
TATAAT (Pribnow box) -10 bp is relative to TSS (probability chart on slide #6)
What is the -35 site?
TTGACAC (relative to TSS)
LOOK AT DRAWINGS
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What product does RNA polymerase II make?
mRNA, snRNA
What are 3 elements required for RNA polymerase recognition of transcription start site?
promoter , enhancer, and transcription factors
What are trans factors?
proteins that recognize and bind specific DNA sequences
What product does RNA polymerase I make?
rRNA
What are transcription factors?
required to recruit RNA polymerase to the promoter
What does prokaryotic transcription result in?
single-stranded RNA
How does transcription termination occur in bacteria?
termination transcribed into RNA causes newly formed transcript to fold back on itself (hair pin)
What does termination depend on sometimes?
the rho termination factor
Where is the starting point of transcription?
transcriptional start site (TSS)
