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Blueprint Series

Complete Solution
Chapter 10

10
POST-TRANSCRIPTIONAL
GENE CONTROL

REVIEW THE CONCEPTS
1
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2
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Enzymes involved in mRNA capping, splicing, and polyadenylation are
recruited to the phosphorylated CTD, which activates them
...

3
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Because of these sequences, the snRNPs of the spliceosome are recruited to
the proper location on the mRNA
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While RNA nucleotides have an OH group at both
the 2’ and 3’ carbons, the 3’ carbon of the branch point A is connected to an adjacent
nucleotide
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4
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Small nuclear
RNAs (snRNAs) bind to splice sites and participate in splicing reactions
...

Micro RNAs (miRNAs) and short, interfering RNAs (siRNAs) are involved in
gene silencing
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5
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In group II intron self-splicing, the introns alone form
a complex secondary structure involving numerous stem loops, whereas spliceosomal splicing utilizes snRNAs interacting with the 5’ and 3’ splice sites of
pre-mRNAs, which form a three-dimensional RNA structure functionally analogous to the group II intron
...
In these experiments, domains I and V are deleted,
and this yields a group II intron incapable of self-splicing
...
This shows that portions of group II introns can
be trans-acting like snRNAs
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In muscle cells, the internal polyadenylation site could be spliced out of the
mature RNA when the fifth intron is removed
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In other cells, the fifth intron may not
be spliced out
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In this scenario, a muscle-specific splicing factor could facilitate
removal of the fifth intron
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RNA editing is a type of pre-mRNA processing, altering the sequence of the premRNA that results in a mature mRNA differing from the exons encoding it in
genomic DNA
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A case for RNA editing in humans
involves the serum protein apoB, which forms large lipoprotein complexes that
carry lipids in serum
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RNA editing occurs in intestinal
cells, where a single base alteration converts a codon for glutamine into a stop
codon
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8
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These bilayers are
amphipathic in nature, so it is extremely unfavorable for hydrophilic molecules
to diffuse through
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9
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NXF1 binds in
multiple places along mRNPs, together with other mRNP adapter proteins,
including REF (RNA export factor) and SR proteins
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Protein kinases and phosphatases are thought to

CHAPTER 10: Post-Transcriptional Gene Control 39

play a key role in the directional movement
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In the cyto- plasm, however, a kinase phosphorylates the adapter
proteins, promoting the dissociation of the exporter from the mRNP
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10
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siRNAs contain 21–23 nucleotides
hybridized to each other sothat two bases at each of the 3’ ends are
single-stranded
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It then base-pairs with itstarget RNA and induces
its cleavage, thereby eliminating the endogenous mes- sage
...
Thisloss of activity causes abnormally high and unregulated
levels of Rheb-GTP, which when bound to the mTOR complex would
result in a high, unregulated activity of mTOR serving as an active
kinase to phosphorylate a variety of sub- strates required to promote
cell growth
...
A plant deficient in Dicer activity shows increased susceptibility to RNA
virusesbecause Dicer is not present to degrade a portion of the viral
double-stranded intermediates that viruses synthesize during
replication
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12
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This results in removal of the
5’ cap, at which point the mRNA is degraded by nucleases from both the
5’ and 3’ ends
...
Finally,
it is possible for nucleases to degrade from within the mRNA and not at
the 5’ or 3’ ends
...
They are full of mRNA processing enzymes
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13
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Traditionally, it was
thought that translation happens either in the cytoplasm or the ER, at
which point the protein would be directed to its area of function
...
Ash1, a protein that inhibits mat-ing type switching in
yeast, has been shown to localize to the bud tip so that it
is only present in the smaller daughter cells after budding
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