Unit 2 Lecture 4 Flashcards
What happens in transcription?
RNA polymerase enzyme transcribes DNA into RNA (polymerizes RNA)
What are the 3 basic steps of transcription?
- RNA POL binds to a region called a promoter
- transcription starts at a position called the +1 site/transcription start site (where RNA POL transcribes the first base/nucleotide, then reads template)
- transcription stops after the RNA POL passes through a region called the terminator, releasing mRNA transcript
In transcription, which direction does RNA POL move?
moves along the template DNA 3’ to 5’
In transcription which direction is newly synthesized RNA made?
5’ to 3’
What is another name for the non-template strand of DNA?
coding strand
because it resembles the mRNA that encodes the protein
Which direction is the DNA template read?
3’ to 5’
What does promoter activity do?
controls gene expression
Describe the promoter of bacteria.
- promoter sequence has 2 key sequences: -10 box and -35 box
- all genes require these regulatory sequences
- other regulatory sequences, activation/repression will further control
Describe the promoter of eukaryotes.
- promoter sequence has the TATA box (ie. a TATA repeat sequence: 5’-TATAAA-3’
- all genes have these, plus other regulatory sequences
Describe the first basic step (previously mentioned) of transcription in bacteria.
where RNA POL binds to the DNA upstream of transcription start +1 site in the promoter region
What do the -10 and -35 box do?
they are sigma factor binding sites that recruit RNA polymerase
What is a sigma factor?
a protein that binds to the -35 and -10 box and recruits RNA POL to bind and initiate transcription
sigma binds first, then RNA POL can bind
Describe the first basic step (previously mentioned) of transcription in eukaryotes.
- initiation of transcription occurs at eukaryotic promoter
- general transcription factors bind to the promoter
- transcriptional activator proteins bind to enhancers
- basal transcription complex (ie. minimum complex needed to initiate transcription): TATA binding protein and mediator complex bind to the promoter to recruit binding of RNA POL
Describe the second basic step (previously mentioned) of transcription.
transcription starts and RNA polymerase reads template DNA to make RNA
- transcription starts downstream of promoter at the first base pair that is transcribed into RNA
- bacteria: +1 site, about 10 bases downstream from -10 box
- eukaryotes: transcription start site, the first base RNA POL will transcribe into mRNA
- RNA polymerase enzyme transcribes DNA and polymerizes RNA
What is RNA POL made up of?
several protein subunits
What does RNA POL bind to?
promoter region
How does RNA POL read the DNA template?
from 3’ to 5’
What does RNA POL do?
separates the strands of DNA and catalyzes the addition of new bases (first base copied into mRNA is +1 site or transcription start site
Describe the third basic step (previously mentioned) of transcription.
transcription starts after RNA POL passes through the DNA region called the terminator
- terminator or termination sequence is a sequence found on DNA
- part of termination sequence is copied into the 3’ untranslated region of RNA and makes a hairpin loop that helps stop transcription
Summary of transcription mechanism in bacteria.
- initiation of transcription happens at the promoter sequence
- sigma factor protein binds to the promoter (ie. sigma factor binds to -10 and -35 boxes
- this helps recruit RNA POL to bind and promote the start of transcription
- RNA POL bound to DNA is orientated such that the catalytic site (catalyzes the phosphodiester bonds
- first base that serves as template to transcribe into RNA is called the +1 site
Summary of transcription mechanism in eukaryotes.
- initiation of transcription happens at the promoter sequence with TATA box
- general transcription complex are proteins (factors) that assemble at promoter (ie. TATA Binding Protein (TBP))
- these help RNA POL to bind and promote transcription, called the basal transcription complex
- regulatory transcription factors (ie. activators, repressors bind to DNA sequences (enhancers, promoter proximal elements) and regulate transcription)
- first base that serves as the template to transcribe into RNA is called transcription start site
Describe DNA packaging (transcriptional control) in bacteria.
promoters are unpackaged, hence accessible to RNA POL so “default” state is always on
Describe DNA packaging (transcriptional control) in eukaryotes.
DNA is packaged tightly and must be unpackaged (decondensed) for RNA polymerase to access DNA and start transcription
Describe DNA packaging (transcriptional control).
- recall that eukaryotic DNA is packaged into chromatin
- condensed chromatin means transcription is “off”
- transcription is “on” only when DNA is decondensed
When does transcription and translation occur in bacteria?
happen at the same time, translation begins even before transcription is completed
Describe eukaryotic mRNA processing: before mRNA is exported to cytoplasm…
- addition of 5’ CAP (consists of 7-methylguanosine attached in a 5’ to 5’ phosphate linkage
- polyadenylation: forming a poly A tail added to the 3’ end
- removal of introns and splicing of exons: introns are excised from the RNA strand and exons are spliced together
