chapter 38 Flashcards
what are the 3 ways rRNA and tRNA are modified
- The final mature RNA is cleaved from a larger precursor
molecule. - Many tRNA transcripts lack the CCA sequence at the 3′ end of
the strand. These nucleotides are added post-transcriptionally. - The bases and riboses of tRNA and rRNA are modified, for
instance, by the attachment of methyl groups.
RNA polymerase I synthesizes what
large precursor RNA (45S)
RNA (45S) is processed to yield what
18S, 28S, 5.8S rRNAs
what does snoRNP do
catalyze reactions in the nucleolus that modify and alter the large precursor RNA (45S)
RNase P removes nucleotides from what end of the precursor
5’
RNase T removes nucleotides from what end of the precursor
3’
CCA-adding enzyme adds nucleotides to what end of the precursor
3’ end
how is the 5’ end of the pre-mRNA transcript modified
a 5’ cap is added
what is the purpose of the 5’ cap
increases mRNA stability by protecting the 5’ end from phosphatases and nucleases
5’ cap enhances
translation of mRNA
how is the poly A tail form
3’ end is cleaved by a specific endonuclease and a stretch of polyadenylate is added by poly A polymerase
3’ poly A tail is beneficial how
increases mRNA stability and enhances the translation
exons are what kind of region
coding regions
introns are what kind of region
noncoding regions
what are the 3 common features of intron-exon junctions
- The 5′ end of the junction has the sequence 5′AGGUAAGU3′, with the
first GU from the 5′ end demarcating the beginning of the intron. - The 3′ end of the intron is marked by a stretch of pyrimidines
(polypyrimidine tract) followed by any base, a C, and then the intron ends
with AG. - The branch site is located 20–50 nucleotides from the 3′ end of the
intron.
when does RNA splicing begin
the cleavage of the phosphodiester linkage between
the upstream exon (exon 1) and the 5′
end of the intron
what is the attacking group in RNA splicing
The attacking group
is the 2′-OH of an adenylate residue at
the branch site. This is a
transesterification reaction
what kind of reaction is RNA splicing
This is a
transesterification reaction
the transesterification reaction generates and forms what
generates a branch and forms a lariat intermediate
how are the two exons joined together in RNA splicing
The 3′-OH of exon 1
attacks the
phosphodiester linkage
between the intron and
exon 2, joining the two
exons with another
transesterification
reaction.
what is snRNA
small nuclear RNA (<300 nucleotides)
what is snRNP
small nuclear ribonucleoprotein particles
snRNA with associated proteins
spliceosomes are composed of
snRNPs, splicing factor, pre-mRNA being processed
functions of the CTD include
- Recruiting enzymes to
synthesize the 5′ cap. - Recruiting components of the
splicing complex. - Recruiting the endonuclease
that cleaves the pre-mRNA to
expose the site for poly(A)
addition.
what is CTD for dummies
carboxyl-terminal domain of RNA pol II
transcription and splicing coordination
what is a ribozyme
some RNA that function as catalysts
what are examples of ribozymes
RNaseP
snRNAs
rRNAs
