chapter 8 Flashcards
what do rna ribonucleotides contain
ribose sugar, a nucleotide base, one or more phosphate groups
what are the two differences from DNA with RNA?
uracil instead of thymine
- the sugar ribose is used rather than deoxyribose
what is RNA polymerase?
it catalyzes the addition of each robinucleotide to the 3’ end of the growing strand
forms phosphodiester bonds between the nucelotides
a single type of rna catalyzes the transcription of all ______ in _________
RNA; e.coli
rifampicin
inhibits RNA synthesis (in prokaryotes) by inhibiting formation of the phosphodiester bond
what is mRNA
-produced by protein-encoding genes
-short-lived middle man between DNA and protein
what is the only type RNA that undergoes translation?
mRNA
what is the transcription of mRNA often followed by?
post-transcriptional processing
what do functional RNA’s do?
they perform functional/structural tasks, THEY DO NOT ENCODE PROTEINS
tRNA
-encoded in dozens of forms
-is responsible for binding an amino acid and dispositing it for inclusion into a growing protein chain
rRNA
combines with numerous proteins to form ribosomes
snRNA (small nuclear)
found in the nucleus of eukaryotes and play a roll in mRNA processing
miRNA (micro)
in plant and animal cells
involved in post-transcription regulation of mRNA
siRNA (small interfering RNA)
protects plant and animal cells from viruses and movement of transposons
ribozymes
certain RNAs in eukaryotic cells that have catalytic activity
what are the four stages of transcription in bacteria?
- promoter recognition
- transcription initiation
- chain elongation
- chain termination
what is transcription
the synthesis of a single-stranded RNA molecule by RNA polymerase
template strand (non-coding strand)
what the polymerase reads of the DNA to make a complementary, anitparallel strand of ribonucleoties
coding strand (non-template strand)
complementary to the template strand
where is the promoter at the start of transcription?
immediately upstream (5’)
what is the promoter referred to as?
the +1 nucleotide
what is the promoters role?
it is the actual binding site for RNA polymerase
what is the coding region of the gene?
portion that contains information needed to synthesize the protein product
what is the termination region of the gene?
it regulates cessation of transcription
where is the termination region located?
immediately downstream (3’) to the coding segment of the gene
what is the bacterial RNA polymerase holoenzyme composed of?
a pentameric core enzyme that binds a sixth subunit- the sigma subunit
what is the large core enzyme composed of?
sigma1, sigma2, beta, beta’, and one omega subunit
what can’t the core enzyme do without a sigma subunit?
it cannot bind the promoter or initiate RNA synthesis
what are the other types of sigma subunits called?
alternative sigma subunits
what do alternative sigma subunits do?
alter core enzyme conformation in slightly different ways to facilitate association with different types of promoters
what is a promoter?
a double stranded DNA sequence that the RNA polymerase binding site
where is the promoter located for bacterial (prokaryotic) things
a short distance upstream of the coding sequence. within a few nucleotides of +1
where does the RNA polymerase bind to the consensus sequence?
within the region of the promoter
what is the prinbow box or -10 consensus sequence?
a six base pair region in the promoter at the negative 10 nucleotide
5’-TATAAT-3’
what is the -35 consensus sequence?
5’-TTGACA-3’
what does RNA Polymerase bind to in a prokaryotic promoter sequence?
-10 and -35 sequences and occupies the space between and around them
Transcription Initiation
- holoenxyme makes loose attachment to the promoter sequence to form the closed promoter complex
- holoenzyme unwinds about 18bp of DNA around the -10 position to form the open promoter complex
- holoenzyme progresses downstremm to initiate RNA synthesis at the +1 site
what does alternative sigma subunits allow for?
holoenzyme binding to variant promoters
how long is the transcrption bubble in trancription elongation?
18 nucleotides
when do the sigma subunits dissociate?
after the first 8 to 10 RNA nucleotides are polymerized
what happens to the core enzyme after trascription is completed?
the 3’ end of the RNA trails off the core enzyme and becomes dissociates from the DNA
what is a dna termination sequence
a repeating sequence that teriminates the transcription in bacteria
intrinsic termination
the repeated sequence induces secondary structures in the newly formed RNA that induce termination
rho-dependent termination
uses a different termination sequence and the rho protein (small GTPase)
what is the rho enzyme do?
an additional enzyme that helps induce termination
how does most bacteria termination occur?
via intrinisc termination
what is a hairpin
a short stem-loop structure
what is intrisic termination
where termination sequences include an inverted repear followed by a string of adenines
what is the hairpin followed by?
a series of Us in the mRNA that causes the RNA polymerase to slow down and destabalize
what induces the polymerase to release the transcript and seperate from DNA?
the instability caused by the slowing polymerase and the U-A base pairs
rho-dependent termination does not have a string of ______
uracils
what does rho-dependent termination instead of uracils?
rho utilization site (rut site) a stretch of about 50 nucleotides rich in cytosine
how are rho proteins activated?
by ATP binding to one of the functional domains, faciliating binding to the rut site
rna polymerase I
transcribes three ribosomal RNA genes
how many polypeptides do rho proteins contain?
6 identical polypeptides with two functional domains each
rna polymerase II
transcribes protein coding genes (mRNA) and most small nuclear genes
rna pol III
transribes tRNA, one small nuclear RNA, and one ribosomal RNA
