Transcription Flashcards
what is the one gene one enzyme hypothesis
a single gene codes for one enzyme
DNa dependent synthesis of RNA or the use of DNA as a template to synthesize RNA
transcription
percent of genes in prokaryotes
3-30%
percent of genes in eukaryotes
1-10%
a sequence of 20-200 bases “upstream” from a gene that serves as a recognition site for binding RNA polymerase
promoter
promoter contains these regions that identify the region as a promoter
consensus sequeces
where are the consensus sequences located
-35 and -10 nucleotides from the promoter
the promoter occurs on the ____ strand
nontemplate
the enzyme that “reads” DNA to synthesize RNA
RNA polymerase
core enzyme of RNA polymerase
two alphas
beta
beta prime
omega
subunit for DNA binding
beta prime
subunit for the catalytic site
beta
subunit that deals with promoter binding, assembly and regulation
alpha
subunit that deals with structural role, restores activity
omega
promoter recognition that transiently bind to core enzyme to allow binding to correct strand and initiation site
sigma factor
three stages of transcription
initiation
elongation
termination
RNA polymerase binds to promoter causing _____ and _____
strand separation and unwinding
Initiation is complete after
about 10 NTPs have been added
what continues as the sigma factor falls away
elongation
An ATP dependent helicase that catalyzes the unwinding of RNA:DNA duplex hybrids during transcription to promote termination of prokaryotic transcription
Rho factor
terminator makes this structure in prokaryotes
hairpin structures
five points about eukaryotic transcription
- three different RNA polymerase that cannot initiate transcription
- promoters are more complex that consensus sequences
- initiation requires many transcription factors to activate RNA polymerase
- regulatory elements modify gene expression
- transcripts require considerable processing prior to translation
location and function of RNA polymerase I in eukaryotes
located in nucleolus
transcribes large rRNAs
location and function of RNA polymerase II in eukaryotes
located in nucleus
transcribes mRNAs and snRNAs
location and function of RNA polymerase III in eukaryotes
located in the nucleus
transcribes tRNAs and 5s rRNAs
position and description of TATA box
-25
indicates transcription start site
position and description of CAAT box
-50
indicates “strong” promoter (makes a lot of mRNA)
location and description of GC box
-80
indicates “housekeeping” genes
code for proteins needed all the time
housekeeping genes
eukaryotic initiation involves
several transcription factors
transcription factors sequentially bind to
TATA region and polymerase
polymerase complex binds to
promoter
activates polymerase via phosphorylation and transcription begins
TFIIH
a short segment of DNA near eukaryotic promoters that bind transcription of certain genes
enhancers
what allows for the interaction with RNA polymerase
formation of DNA loop
do mRNA’s require processing in prokaryotes
no
three main types of mRNA processing in eukaryotes
5’ capping
3’ polyadenylation
splicing
addition of 7-methyl guanosine to the 5’ end
5’ capping
the addition of 100-250 adenylate residues to the 3’ end
3’ polyadenylation
the removal of introns and ligation of exons
splicing
two characteristics of 5’ cap
- methylguanosine linked via 5’ to 5’ triphosphate
2. 2’ OH’s of up to 3 neucleotides are methylated
5’ cap serves as a
recognition site for ribosome attachment and prevents transcript degradation by exonucleases
what is the termination sequence of eukaryotic RNAs
AAUAAA
two big functions of the poly A tail
help direct mRNA’s out of the nucleus
protects 3’ end from exonuclease degradation
what does the length of the poly A tail say about the RNA
describes its longevity
pre-mRNAs have short nucleotide sequences at the end of introns that serve as
splicing signals
recognize consensus splice sites via RNA base pairing
snRNPs
what makes a spliceosome
several snRNPs join together
job of spliceosomes
cut out and attaches exon ends together
where does RNA splicing occur
in in the nucleus
introns may provide
cross over recombination sites
facilitate recombination within proteins to allow novel protein function
exon shuffling
