L8. Intracellular compartments & transport II Flashcards
explain how proteins are glycosylated in the ER
- they are glycosylated on asparagines and serines
- they are glycosylated by the addition of a sugar group
- the part of the protein that is getting the sugar faces ER lumen
- the part the has the sugar will end up outside when it gets to the plasma membrane
what happens to misfolded or unfolded proteins in the ER
- they bind to chaperon proteins in the ER and are retained there
- if they fail to refold properly, they are transported back to the cytosol and are degraded
what happens when there is an accumulation of misfolded proteins
- the proteins are recognized by transmembrane sensor proteins in the ER membrane
- each activates part of the Unfolded Protein Response (UPR)
accumulation of misfolded proteins - what is the Unfolded Protein Response (UPR)
- can be direct or indirect
- some of the transmembrane sensor proteins will stimulate transcriptional regulators of chaperon-encoding genes
- others may inhibit protein synthesis, reducing the flow of protein through the ER
what are the types of coated vesicles
- clathrin-coated
- COP-coated: COPI and COPII
coated vesicles: clathrin-coated - what are the coat proteins
- clathrin + adaptin 1
- clathrin + adaptin 2
coated vesicles: clathrin + adaptin 1 - what is the origin and the destination
- origin: Golgi
- destination: lysosome (via endosomes)
coated vesicles: clathrin + adaptin 2 - what is the origin and the destination
- origin: plasma membrane
- destination: endosomes
coated vesicles: COP-coated - explain COPI
- retrograde transport
- goes backward
- from Golgi to ER
coated vesicles: COP-coated - explain COPII
- anterograde transport
- goes forward
- from plasma membrane to endosomes
transport with clathrin-coated vesicles - how is the budding initiated
- cargo receptors with their bound cargo are captured by adaptins
- they then bind to clatherin molecules to the cytolytic side and budding initiates
transport with clathrin-coated vesicles - what happens after budding starts
- dynmin proteins assemble around the neck of the budding vesicle
- they are GTPAses and they hydrolyze their bound GTP
- with the help of other proteins, it pinches off the vesicle
transport with clathrin-coated vesicles - what happens after budding finishes
coat proteins are removed and the naked vesicle can fuse with its target membrane
transport with clathrin-coated vesicles - what happens as the vesicle fuses with the target membrane
- tethering
- docking
- fusion
transport with clathrin-coated vesicles - tethering
- a tethering protein on the target membrane must bind to a Rab protein (monomeric GTPAse) that is on the surface of the vesicle
- provides the initial recognition between the vesicle and the target membrane
- this allows docking to happen
transport with clathrin-coated vesicles - docking
- v-SNARE on the vesicle binds with the t-SNARE on the target membrane
- this ensures that the vesicles dock at their appropriate target membrane
transport with clathrin-coated vesicles - fusion
- Release of calcium from volted gated calcium channels activates SNARE fusing with membrane
- the complimentary SNARE proteins catalyze the final fusion of the two membranes
transport with clathrin-coated vesicles - how do SNAREs catalyze fusion of membranes
- the pairing of the SNAREs force water molecules out
- this allows lipids to flow together to form a continuous bilayer
transport with clathrin-coated vesicles - what happens to the SNAREs after fusion
SNAREs are pried apart so they can be used again
explain the structure of the Golgi
- cis Golgi network = faces ER
- trans Golgi network = faces PM
explain the exocytosis pathways in secretory cells
- many proteins are constitutively secreted
- specialized secretory cells undergo regulated exocytosis and the pathways diverge in the trans Golgi
exocytosis pathways in secretory cells - what are the two pathways
- constitutive secretion = unregulated and does not require a signal for the vesicle to release contents
- regulated secretion = regulated and requires a signal for the vesicle to release contents
- mechanisms unclear
explain receptor-mediated endocytosis
- ligand binds to receptors on the surface of the cell and it will be internalized in clathrin-coated vesicles
- vesicles will then lose their coat and fuse with endosomes
- bc of the acidic environment, the ligand dissociates from the receptors
- ligand will then go to the lysosome and is degraded
receptor-mediated endocytosis - what are the fates of the receptors
- recycling
- degradation
- transcytosis
receptor-mediated endocytosis: what are the fates of the receptors - recycling
retrieved receptors are return to the same membrane they came from
receptor-mediated endocytosis: what are the fates of the receptors - degredation
receptors that are not received go to the lysosome and are degraded
receptor-mediated endocytosis: what are the fates of the receptors - transcytosis
retrieved receptors that go to a different domain of the plasma membrane
receptor-mediated endocytosis - how do lysosomes degrade ligands
- the lysosome contains hydrolytic enzymes that are only active under acidic conditions
- the acidity is maintained by a proton ATPase
receptor-mediated endocytosis - proton ATPase
- it hydrolyses ATP to move proton from PM into endosomes
- causes a reduction in pH and increases acidity
- this then causes the degrative enzymes to be turned on
what is phagocytosis
- it is a form of feeding in protozoa
- phagocytic cells can take up large molecules
phagocytosis - how can phagocytic cells take up molecules
- Affirmation of pseudopod will wrap its membrane around target and engulf it
- Will then fuse with lysosomes and breakdown contents
what is autophagy
- the cell eats itself
- process begins with an enclosure of the organelle by a double membrane creating an autophagosome
- then it fuses with a lysosome
explain the cell’s route to degradation
early endosomes, phagosomes, and autophagosomes can fuse with lysosomes or late endosomes for degradation
