Chapter 8: Transcription Flashcards
the copying of one strand of the DNA (the coding strand) into an RNA molecule (transcript)
transcription
enzyme that transcribes DNA into RNA
RNA polymerase
RNA polymerase copies the coding strand of DNA by using the ()
complementary (template/non-coding) strand
RNA polymerase separates the DNA strands and allows () to base pair with template strand
ribonucleoside triphosphates
types of RNAs that are produced
- mRNA (encode proteins)
- non-coding RNAs (regulatory, catalytic, or structural roles)
3 stages of transcription
- initiation
- elongation
- termination
transcription starts when RNA polymerase binds to DNA sequence just preceding the gene: (); signifies start site for transcription
promoter
first base to be transcribed; denoted +1
transcription start site (TSS)
if RNA is transcribed in the 5’ to 3’ direction, the template must be read in the () direction
3’ to 5’
on the RNA, bases 3’ of a site are (1), while bases 5’ of a site are (2)
- downstream
- upstream
during initiation, RNA polymerase separates DNA strands to make a ()
transcription bubble
during initiation, the first few ribonucleoside triphosphates are added while ()
RNA polymerase is still at promoter
RNA polymerase moves past promoter and changes conformation to be more stably associated with DNA when RNA is ()
a sufficient size
transcription stage where RNA polymerase moves along the DNA, adding ribonucleotides
elongation
how is the transcription bubble maintained during transcription elongation
DNA re-pairs behind RNA polymerase as the enzyme unwinds DNA ahead
elongation continues until the polymerase meets a DNA sequence called a () that signals RNA synthesis to cease
terminator
in chromatin-packaged DNA, () prevent transcription machinery binding to DNA
nucleosomes
3 additional types of enzymes required in eukaryotic transcription
- nucleosome remodeling enzymes
- histone chaperones
- enzymes that reversibly modify histone proteins
enzymes that reposition histones away from DNA to be transcribed; can also work to block transcription
nucleosome remodeling enzymes
enzymes that disassemble and reassemble the histone octamer
histone chaperone
some enzymes can reversibly modify histone proteins; these modified proteins ()
recruit specific proteins to certain DNA regions
eukaryotes have 3 RNA polymerases
RNA polymerase I to III
eukaryotic RNA polymerase that transcribes large ribosomal RNA (rRNA) genes
RNA Pol I
eukaryotic RNA polymerase that transcribes messenger RNA (mRNA) genes
RNA Pol II
eukaryotic RNA polymerase that transcribes a variety of RNAs including transfer RNAs (tRNAs) and 5S ribosomal RNA
RNA Pol III
() have a 4th RNA polymerase that transcribes regulatory RNAs
plants
number of polymerases in bacteria and archaea
1
all RNA polymerases have a core enzyme that (1), but this cannot act alone and relies on extra proteins; same basic core structure is conserved between (2)
- catalyzes RNA synthesis
- 3 domains of life
(1) polymerase is the smallest polymerase, with 5 subunits: (2)
- bacrterial
- 2 alpha, 1 beta, 1 beta’, 1 omega
the () subunits of bacterial RNA polymerase form a jaw-like structure
beta and beta’
the () subunit of bacterial RNA polymerase has an N-terminal domain and C-terminal domain joined by a flexible linker
alpha
additional function of RNA Pol II in eukaryotic and archaeal transcription
couples transcription to the processing of the RNA transcript
the () of Poll II is crucial to the coupling of transcription to RNA transcript processing
C-terminal domain (CTD)
core bacterial RNA polymerase requires an extra subunit called () directly contacts (and directs enzyme to) the promoter
sigma factor
in bacterial RNA polymerase, core enzyme + sigma factor = ()
holoenzyme
type of bacterial sigma factor that recognizes promoter sequence for housekeeping genes as well as promote their transcription
primary sigma factor
type of bacterial sigma factor that recognizes promoters for genes whose expression is regulated in response to specific signals or stress conditions
alternative sigma factor
2 elements of bacterial promoters
-35 and -10 elements
some bacterial promoters have extra recognition sequences, like ()
AT-rich UP element
some bacterial promoters have sub-optimal (shorter or nonexistent) -35 elements, which results in ()
extended -10 element
factors that promote sigma factor’s specificity -> regulates bacterial transcription
each sigma factor has preferred binding sequence and preferred spacing element between -35 and -10 elements
in the RNA polymerase holoenzyme, there are 3 sigma domains that are positioned to recognize specific promoter elements
- Domain 2
- Domain 3
- Domain 4