NROS 310 Exam 2 Study Sets || All Answers Are Correct 100%.
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Course
NROS 310
Institution
NROS 310
Why is it important that proteins get targeted to the right cellular location? (11) correct answers Each protein has a specific function at its intended destination in the cell and failing to complete that task can result in the cell not functioning properly. Ex. in cystic fibrosis the CFTR protein...
NROS 310 Exam 2 Study Sets || All Answers Are Correct
100%.
Why is it important that proteins get targeted to the right cellular location? (11) correct answers
Each protein has a specific function at its intended destination in the cell and failing to complete
that task can result in the cell not functioning properly. Ex. in cystic fibrosis the CFTR protein is
not able to reach the membrane leading to fluid buildup in the lungs.
How do proteins get to the appropriate targets within the cell? (11) correct answers Specific
sequences of amino acids can serve as a signal sequence for the destination of the protein.
There are also 3 protein transport methods.
1. vesicle transport - proteins are placed into vesicles and walked to their destination by motor
proteins.
2. transmembrane transport - proteins are transported using the continuous membrane
3. gated transport - gated transport of proteins from the cytosol to the nucleus
What kind of molecules can pass unaided through the nuclear pore complex? (11) correct
answers small molecules (5kd or less)
What is the nature of the nuclear localization signal (NLS)? (11) correct answers signal sequence
of 5 amino acids (lys-lys-lys-arg-lys) that is recognized by importin allowing the protein to be
imported into the nucleus
Design an experiment to show that a given signal sequence is both necessary and sufficient to
target a protein to the nucleus. (11) correct answers To determine if it is necessary, knock the
sequence off and tag it with GFP (green fluorescent protein) and see if it is able to enter the
nucleus. If it can not enter the nucleus the sequence is necessary for import. You should also do
step-by-step substitutions of each amino acid in the signal sequence and tag the protein to prove
that the specific signal sequence is necessary.
To determine if the signal sequence is sufficient to target a protein, add the signal sequence to
any protein that does not import into the nucleus under normal circumstances and tag it. If that
protein is able to enter the nucleus, the signal sequence is sufficient to import proteins into the
nucleus.
What does it mean if your results show that a protein sequence is necessary but not sufficient?
(11) correct answers A protein sequence that is necessary but not sufficient would require other
factors or conditions to be successfully imported into the nucleus. For example, the signal could
be part of a patch that must be folded a specific to be recognized or the signal might be required
to be surrounded by specific amino acids.
, What is the difference between a signal patch and a signal sequence? (11) correct answers 1.
Signal sequences have one stretch of multiple amino acids while signal patches are multiple
amino acids located at different locations along the protein that come together when the protein
is folded.
2. Signal sequences are cleaved off when the protein reaches its destination while signal patches
are not cleaved.
3. Signal patches require the protein is folded a certain way to be functional. Signal sequences
are functional even when the protein is unfolded.
Can nuclear localization signals be regulated? If so, how? (11) correct answers Yes. If the NLS is
covered it will not be able to bind importin and enter the nucleus.
This is regulated by protein phosphatase calcineurin which exposes the NLS only when the cell
has high levels of calcium.
Describe how small g-proteins are regulated? (12) correct answers The function of g-proteins
depend on what form they are in (either GTP or GDP). When g-proteins bind GTP they are
active, while g-proteins binding GDP are inactive. Factors known as GEF and GAP mediate the
transformation between these two states.
For example, RAN-GAP converts RAN-GTP => GDP, while RAN-GEF handles RAN-GDP to
RAN-GTP
Describe how the actions of RAN mediate import of proteins into the nucleus? (12) correct
answers When cargo in the cytosol with a NLS approach the nuclear pore, the cargo binds to
importin which transports it into the nucleus.
RAN-GTP dissociates the cargo and importin and binds to importin and takes it back into the
cytosol. In the cytosol, it is changed to RAN-GDP, which then dissociates with importin as
importin has no affinity for RAN-GDP.
Without RAN, importin would not be able to dissociate from cargo or return to the cytosol to be
recycled.
Describe how the actions of RAN mediate export of proteins out of the nucleus? (12) correct
answers Cargo with a nuclear export sequence will bind to both exportin and RAN-GTP. This 3-
way complex is required to leave the nucleus. Once in the cytosol, RAN-GAP will turn RAN-
GTP into RAN-GDP allowing all 3 to dissociate and allowing exportin to return to the nucleus.
Without RAN, cargo would be unable to exit the nucleus or dissociate from exportin. Exportin
would also not be able to return to the nucleus to be recycled.
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