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69 Cards in this Set

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  • Back
Basic set of membrane-enclosed-compartments
Rough ER~9%
Smooth ER~6%
Lysosomes~ 1%
about 50%
site of protein synthesis and degradation
performs most of the cells intermediate metabolism
about 22%
generate most ATP that cell uses
about 1%
contain enzymes used in various oxidation reactions
nucleus equivalent to
ER equivalent to
golgi apparatus
mitochondria equivalent to
plastids equivalent to
proteins can move between compartments in different ways
gated transport
transmembrane transport
vesicular transport
most organelles are generated by
growth and division of existing organelles
3 main ways proteins can move into membrane bound compartments
1)gated transport
2)transmembrane transport
3) vesicular transport
gated transport
transport into and out of the nucleus
transmembrane transport
import into ER, mitochondria, plastids, peroxisome
vesicular transport
transport between ER, golgi, outermembrane
2 types of signal
signal sequences- continous stretched of aas that are recognized when folded
signal patches-stretches of aas that arent recognized by as signals until folded
general properties of signal sequence to ER
N-term, removal of sequence, core of 6-12 hydrophobic amino acids
general properties of signal sequence mitochondria
N-term, removal of sequence, amphipathic helix, Arg and Lys residues on one side, hydrophobic residues on other
general properties of signal sequence to choloroplast
N-term, removal of sequence, no common motifs
general properties of signal sequence to peroxiomes
C-TERM, NO removal of sequence,PTS1 signal at C-term PTS2 at N-term
antigen is recognized by
calcineuron gets activated when bound to
How is the signal exposed
Calcineuron cleaves NF-AT
dissassembly of nuclear envelope due to
TOM complex is required for
import of ALL nucleus-enclosed mitochonrial proteins
on outer membrane
The TIM23 complex
transports some of these proteins into the matrix space, helps insert transmembrane proteins into inner membrane
TIM 22 complex
mediates insertion of a subclass of inner membrane proteins
OXA complex
mediates the insertion of inner membrane proteins synthesized in the mitochondria
mitochondrial precursor proteins are imported as
unfolded polypeptide chains
T/F like the lumen of the ER, the interior of the nucleuys is topologically equivalent to the outside of the cell
false. flow of material does not have to cross a bilayer in nucleus but does in ER
membrane-bound and free ribosomes, which are structureally and functionally identical, differ only in the proteins they happen to be making at a particular time
true. ribosomes all begin translating mRNAs in cytosol
to avoid the inevitable congestion that would occur if two-way traffic through a single pore were allowed, nuclear pore complexes are specialized so that some mediate import while others mediate export
false. Individual nuclear pores mediate in both directions.
peroxisomes are found only in a few specialized types of eukaryotic cells
false, found in all
in multipass membrane proteins, the odd numbered transmembrane segments act as start-transfer signals and the even numbered act as stop-transfer signals
False. the most N-terminal acts as a start transfer signal
what is the fate of a protein with no sorting signal?
it will remain in the cytosol
imagine you have engineered a set of genes, each encoding a protein with a pair of conflicting signal sequences that specify different compartments. If the genes were expressed in a cell, predict which signal would win out for the following combos
A. Signal for import to nuclues and import to ER. The protein would enter the ER. The signal for import to ER is located at the N-term and functions before the internal signal for nuclear import is synthesized.
B. Signals for import into peroxisomes and import to ER. Import to ER is located at N-term and functions before the internal signal for peroxisomes is synthesized.
C. signals for import into mitochondria and retention in ER. Protein would enter mitochondira because in order for retention in ER, protein must be imported into ER but there is no ER import signal
D. Signals for import into nucleus and export from nucleus. It would shuttle between the cytosol and nucleus. These signals do not really conflict
What portion of the nucleoplasmin molecule is respobsible for localization in nucleus?
This portion is in the tail.
How do these experiments distinguish between active transportm in which a nuclear localization signal triggers transport by the nuclear pore complex, and passive diffusion
these experiments suggest that the nucleoplasmin tail carries a nuclear localization signal and that accumulation in the nucleus is not the result of passive diffusion. The experiment suggests the heads are too large to pass with passive diffusion
Why did you use RANQ69L-GTP instead of RAn GTP?
Ran is a GTPase and will slowly convert GTP to GDP and so you would have had an undefined mixture of GTP and GDP which would confuse the results. By using a form of RAN that cannot hydrolize GTP, you are assured that Ran was in Ran-GTP conformation
Which of the many proteins eluted from the 2 different affinity columns is likely a candidate for the factor that promotes nuclear import of Ran-GDP
since Ran69L-GTP column was not removed, you are looking for a protein that is present in lane 1 but not in lane 2. One such protein is located between 7 kd and 14 kd.
what other protein or proteins would you predict that the ran-GDP import factor would be likely to bind in order to carry out its function
the small protein that binds to Ran-GDP called NTF2. NTF2 binds to Ran-GDP and FG-repeats present in the nucleoporins of the nuclear pore complex. The progressive movement of NTF2 along FG tracks in nucleoporins allows GDP to be deilivred to the nucleus where GEF converts GDP to GTP causing it to dissociate from NTF2 which then dissociates and brings in another Ran-GDP
how might you confirm that the factor you have identified is necessary for promoting the nuclear uptake of Ran?
The info in the problem states only that the cytoplasm passed over a Ran-GDP column is depleted of some factor that is essential. The inference is that NTF2 is the critical factor and so to prove that it is, you need to show that purified Ntf2 can promote the uptake of Ran-GDP into nuclei.
How do you suppose that binding of methotrexate interferes with mitochondrial import?
The binding of methrotrexate to the active site prevents the enzyme from unfolding, which is necessary for import into mitochondria.
Why do mitochondria need a fancy transloactor to import proteins across the outer membrane? Their outer membranes already have large pores formed by porins
These pores are large enough for all ions and metabolic intermediates but not large enough for most proteins
Where is catalase located in cells without peroxisomes? Why does catalase show up as small dots of fluorescence in normal cells?
it is located in the cytosol of peroxisome-deficient cells. It appears as small dots because its located in perozisomes which are small and distributed throughout cytosol
What would you predict would be the effect of converting the first hydrophobic transmembrane segment to a hydrophillic segment?
It would give rise to a protein with N-term in the cytosol but all other segments in their original location.
How is symmetry generated in ER and asymmetry generated in plasma membrane?
Symmetry of phospholipids in the 2 leaflets of ER membrane is generated by a phospholipd translocator, called scrambalase, that rapidly flips phospholipids of all types back and forth between monolayers of the bilayer. The plasma membrane contains a different kind of translocator which is specific for phospolipids containing free amino groups. These flippases remove these specific phospholipids from external and transfer them to internal and so it is asymmetric,
List the organelles in animal cell that obtain their proteins via gated transport, trasnmembrane trsnport, and vesicular transport
Gated- nucleus
Transmembrane- ER, mitochondria, peroxisomes
Vesicular- Golgi apparatus, endosomes, lysosomes
Which type of protein synthesis, in cytosol or ER do you think is responsible for the majority of protein synthesis in a liver cell?
One way to approach this problem is to compare the relative volumes of the
compartments that are served by cytosolic and ER protein synthesis. The compartments that depend on ER protein synthesis—the
ER, Golgi apparatus, endosomes, and lysosomes—account for less than 20%
of the cell volume. On this basis, then, one would conclude that cytosolic pro-
tein synthesis is responsible for the majority of cellular protein synthesis. In cells that do not secrete large amounts of protein, the majority of protein synthesis is likely to occur in the cytosol.
If you think of a protein as a traveler, what kind of vehicle would best describe the sorting receptor?
A taxi- anyone who has the money-the sorting signal-is taken on the journey
If membrane proteins are integrated into the ER membrane by means of protein translocators, which are themselves membrane proteins, how do the 1st protein translocators become incorporated into the ER membrane?
New cell membranes are made by expansion of exist-
ing membranes; the ER is never made from scratch. There will always be an
existing piece of ER with old translocators to integrate the new translocators.
Inheritance is therefore not limited to the propagation of the genome; a
cell’s organelles must also be passed from generation to generation. This is a chicken vs egg question
T/F The nuclear membrane is freely permable to ions and other small molecules under 5000 daltons
true because the membrane has many nuclear pores that allow small water soluble molecules to pass
T/F Some proteins are kept out of the nucleus, until needed, by inactivating their nuclear localization signals by phosphorylation
True. gene regulatory proteins are subject to this
T/F all cytosolic proteins have nuclear export signals that allow them to be removed from the nucleus when it reassembles after mitosis
false. Resident proteins of the cytosol do not have nuclear export signals
How is it that a single nuclear pore complex can efficiently transport proteins that possess different kinds of nuclear localization signal?
because transport is mediated by a variety of nuclear import receptors that are encoded by a family of related genes. Each gene product is specalized for transport of a group of proteins that share structurally similar localization signals. Yet, all the family membares share common features that allow them to interact iwht the nuclear pore complexes
You have modified GFP to carry a nuclear localization signal at its N-term. How might the addition of an inhibitor of nuclear export to such cells resolve this issue.
Proteins with a nuclear export signal also have a nuclear localization signal so these proteins typically shuttle between the nucleus and cytoplasm
Why do you suppose it is critical that nuclear localization signals remain attached to their proteins?
At each mitosis, the contents of the nucleus and cytosol mix after the nuclear envelope dissasembles. When the nucleus reassembles, the nuclear proteins must be selectively reimported. If the signals were removed, the proteins would be trapped in the cytosol after mitosis.
The TOM complex is required for the import of all nucleus-encoded mitochondrial proteins
the 2 signal sequences required for transport of nucleus encoded proteins into the mitochondrial inner membrane via the TIM23 complex are cleaved off the protein in different mitochondrial compartments
False. Only one of the 2 is cleaved, the n-term
import of proteins into mitochondria and chloroplasts is very similar, even the individual components of their transport machinery are homologous, as befits their common evolutionary origin
false. components of the import machinery are not related
Describe in a general way how you might use radiolabeled proteins and proteases to study import processes in osolated, intact mitochondria. What sorts of experimental controls might you include?
Incubate the labeled proteins with isolated mitochondria under the conditions you wish to test, allow time for import, and then treat mixture with a protease. Proteins that arent imported will be digested by proteease.
T/F the signal peptide binds to a hydrophobic site on the ribosome causing a pause in protein synthesis, which resumes when SRP binds to the signal peptide
T/F nascent polypeptide chains are transferred across the ER through a pore in the Sec61 protein translocator complex
T/F the Er lumen contains a mixture of thiol containing reducing agents that prevent the formation of S-S linkages by maintaining the cysteine side chains of th elumenal proteins
false. ER lumen does not contain reducing agents
Some membrane proteins are attached to the cytoplasmic surface of the plasma membrane through a C-terminal linkage to GPI anchor
false. GPE anchored proteins are attached to teh external surface of plasma membranw
explain how mRNA molecules can remain attached to the ER membrane while the individual ribosomes trasnslating it are released and rejoin the cytosolic pool of ribosomes
An mRNA molecule is attached to ER by the ribosome translatting it. The ribosome population is not static and as mRNA moves through ribosomes, those ribosomes that are done traslating dissociate from the 3' end. But the mRNA remains attached to the ER by other ribosomes that are still in the process of translating it
Why are cytosolic Hsp70 chaperone proteins required for import of proteins into mitochondria and chloroplasts but not for cotranslational import into ER
Protein import into mito and chloro occurs as a post-translational event and chaperones are required to keep the newly made proteins in an unfolded conformation so that they can be imported. During co-translational import, the protein is being made and imported at the same time so there is no chance of it folding and no need for chaperones
where would you expect to find microsomes in an electron micrograph of a liver cell
nowhere. Microsomes are generated when cells are disrupted by homogenization
Which one of the following might be expected to increase the effieciency of import if added to the mixtre of a protein and microsomes
cytosolic Hsp70 would be expected to bind to the import protein and aid its unfolding, which will increase uptale.
Compare and contrast protein import into the ER and into the nucleusMo
Most proteins are translocated into ER as they are being made by ribosomes. In all cases, proteins are translocated across the membrane as unfolded polypeptide chains. Proteins import into nucleus after they have been synthesized, folded, and assembled into complexes. Signal sequences for ER import are often cleaved off after import, whereas nuclear localization signals are not.