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21 Cards in this Set
- Front
- Back
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How do vesicles fuse with the correct, targeted organelle or compartment?
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Transport vesicle membranes display v-SNARE proteins - a large protein family.
Target membranes display t-SNARE proteins – another large family Transport vesicles are first temporarily tethered to the targeted membranes by……. tethering proteins aided by……. “Rab” GTP-binding proteins If the v-SNARE and t-SNARE proteins are complementary they will bind, docking the vesicle to the surface of the target compartment The vesicle then fuses with the target membrane. Integral membrane proteins flow into the membrane of the target compartment Soluble proteins are transferred to the lumen of the target compartment |
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The mitochondrial proteins that are synthesized from nuclear DNA are first translated by
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free ribosomes in the cytosol.
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Post-translational protein import into the mitochodrial matrix
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The mitochondrial proteins that are synthesized from nuclear DNA are first translated by free ribosomes in the cytosol.
They have a special N-terminus targeting sequence (the presequence) containing a number of positively charged residues The protein is presented to the outer mitochondrial membrane (OMM) in a relatively unfolded state, stabilized by special chaperones The OMM contains protein import complexes consisting of…. A receptor that recognizes the presequence on the incoming protein A channel to guide the protein through the OMM and IMM and into the matrix. ATP is hydrolysed to drive the unfolding of the protein as it is threaded through the channel. The negative potential in the matrix attracts the positively charged presequence, driving the protein into the matrix. Mitochondrial chaperones in the matrix grab the new protein as it emerges from the channel and refold the protein. picture in notes |
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Post-translational protein import into the chlorplasts
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Similar concept to mitochondrial import but…
Chloroplasts have more internal compartments, so newly synthesized proteins produced by free ribosomes have several signal sequences, which target the protein to the stroma or to the thylakoid |
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Remember that both mitochondria and chloroplasts have their own
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DNA and ribosomes
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talk about some of the proteins that reside permanintly in chloroplasts and organelles.
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Some of the proteins that reside in these organelles, especially the integral membrane proteins, are synthesized entirely within the mitochondrion or chloroplast and incorporated into the organelle’s membranes by mechanisms with a striking resemblance to protein synthesis and transport systems in bacteria.
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Endocytosis
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Endocytosis involves the pinching off of plasma membrane to form vesicles in the cytoplasm
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2 endocytosis categories
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Bulk-flow endocytosis – continuous non-specific uptake of extracellular fluid into vesicles.
Receptor mediated endocytosis – uptake of specific molecules from the extracellular space which are bound to receptor proteins in the endocytotic pit. |
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The endocytotic pathway
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Materials are taken up into clathrin –coated pits in the plasma membrane
The pits form vesicles The vesicles fuse to form early endosomes, where their contents are dissociated from vesicle receptor proteins in an acid environment and are sorted. Plasma membrane proteins, including receptor proteins are transported back to the membrane. Captured extracellular proteins are transported to the late endosomes. In the late endosomes, molecules originally from the extracellular space that were attached to the receptor proteins may be released into the cytosol. These molecules may trigger changes in cellular function. E.g. cholesterol is transported in the bloodstream as part of a Low-density Lipoprotein (LDL) complex. This complex ninds to endocytotic receptor proteins and is taken into endocytotic vesicles. The cholesterol is released inside the cell and affects cell function when the LDL complex is destroyed in the lysosome. |
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how many cells undergo division in an adult human body per second?
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25 million
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. M phase – "mitotic“
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Includes mitosis & cytokinesis (cytoplasmic division into 2 daughter cells)
Only a small percentage of cells in a tissue or cell culture is in mitosis at any given time |
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what about macromolecular synthesis during mitosis
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relatively inactive
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. Interphase
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occupies bulk of cycle: hours, days, weeks or longer, depending on cell type & conditions; divided into
G1 (first gap), S (DNA synthesis) G2 (second gap) Preparations for upcoming mitosis occur during interphase, including replication of cell's DNA; cell often grows in volume during interphase. Cell does active metabolic functions during interphase (glucose oxidation, replication, transcription, translation) |
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3 cells that have lost ability to divide?
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RBC, nerve cells, and muscle,
once diferentiated, they will remain in this state. |
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Cells that normally do not divide; but with right stimuli, make DNA & divide
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liver - induced to divide if surgically remove part of liver
lymphocytes - divide when exposed to right antigen |
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Cells that are normally highly mitotic
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tissues subject to continual renewal by production of new cells (spermatogonia that become sperm, epithelial cells)
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length of cell cycle is highly____?
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variable
<30 min in very rapidly dividing cleaving embryo cells (not mammals, which cleave very slowly) Several months in slowly-growing tissues, like mammalian liver |
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of interphase, which phase is the most varialbe
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G1
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Rapidly growing adult cells typically divide every________________
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12 - 36 hours
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what is Go
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Most cells that have stopped dividing (temporarily or permanently; in culture or in the body) stop before initiation of DNA synthesis in a special G1 state called G0,
A cell must generate an internal signal to go from G0 (or G1) to S; once this happens, the cell completes the round of DNA synthesis & then goes through mitosis |
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There are two main “transition points” in the cell cycle
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Initiation of DNA replication (at transition between G1 & S)
Initiation of mitosis (at transition between G2 & M) |
