Lecture 19 Flashcards
(30 cards)
Transcription
- RNA synthesized on DNA template
- Genetic information stored in DNA is transferred to RNA
- serves as intermediate molecule between DNA and proteins
- each triplet codon is complementary to anticodon of tRNA
RNA polymerase
- an enzyme that directs the synthesis of RNA using a DNA template
- nucleotides contain ribose (ribonucleotides) not deoxyribose
- no primer required for initiation
Transcription results in
ssRNA - single stranded RNA
- template strand is transcribed
- transcription begins with template binding by RNA polymerase at promoter
promoters
specific DNA sequences in 5’ region upstream of initial transcription point
sigma subunit
responsible for promoter recognition
- initiation of transcription
- dissociates from the entire complex after imitation
transcription start site
- DNA double helix is denatured: unwound to make template strand accessible for RNA polymerase
- interaction of promoters and RNA polymerase regulates efficiency of transcription
consensus sequences
DNA sequences homologous (same/identical) in different genes of same organism
Chain elongation
- ribosomes are added to the RNA chain
- sigma subunit dissociated from holoenzyme
- elongation proceeds under direction of core enzyme
Termination
- the RNA core enzyme traverses the entire gene until a termination nucleotide sequence (UAG, UAA, UGA) is encountered
In bacteria:
termination causes newly formed transcribed RNA to fold back on itself (hairpin loop)
Rho (p) termination factor
a protein utilized in the termination of mRNA
Transcription in eukaryotes
- occurs within nucleus (unlike prokaryotes)
- mRNA must leave nucleus for translation
- chromatin remodeling: chromatin must uncoil to make DNA accessible to RNA pol
- RNA polymerases rely on transcription factors (TFS) to scan/bind DNA
Enhancers and silencers…
control transcription regulation
- Found upstream or within or downstream of a gene modulation transcription at distance
How many forms of RNA polymerase do Eukaryotes have
3
- RNA Pol I
- RNA Pol II
- RNA Pol III
Prokaryotes only have 1
RNA polymerase II (RNAP II)
- responsible for transcription of wide range of genes in eukaryotes
- activity of RNAP II is dependent on cis-acting elements and trans-acting transcription factors
- RNAP II core-promoter determines where RNAP II binds to DNA
Regulatory sequences…
influence efficiency of transcription initiation by RNANP II
- proximal - promoter elements
- enhancers
- silencers
- ex) TATA Box
TATA box
- core - promoter element
- binds TATA-binding protein (TBP) of transcription factor TFIID determines start transcription state site
silencers
decrease transcription levels in response o the cell’s requirement for gene product
enhancers
increase transcription levels
transcription factors facilitate…
RNA polymerase II (RNAP II) binding and initiation of transcription
general transcription factors
required for all RNAP II - mediated transcription
transcription activators and repressors
influence efficiency or rate of RNAP II transcription initiation
Eukaryotic mRNAs require…
processing to produce mature mRNAs
The post-transcriptional modifications
- addition of 5’cap (7-mG cap)
- addition of 3’ tail (poly-A tail)
- Excision of introns
