the secretary pathway Flashcards
where are most lipids synthesised
-endoplasmic reticulum
what links the cytoskeleton and plasma membrane
-integral proteins
-this includes fibroblasts, adipocytes, neurones.
But the molecular detail how they’re what individual proteins might be involved might be different
whats the plasma membrane of a cell like
-asymmetry
-phosphotidylserine has a net negative charge- concentrated in the cytoplasmic leaflet of cells under normal conditions
-the movement of phosphorylated serine from the cytoplasmic leaflet of the bilayer to the outside can trigger things like apoptosis, apoptotic recognition by macrophages.
what direction do carbohydrates project
-outwards of the cell
what does scramblase do
-equilibrates lipid- mixes up lipids for symmetrical growth of both layers of the bilayer
whats inserted into the cytosolic membrane
-new ER lipids
-causes one side of the bilayer to become bigger due to phospholipid synthesis adding to cytosolic half of the bilayer- fixed by scramblase (catalyses flipping of the phospholipid molecules)
-leads to symmetric growth of both halves of bilayer
what ensures membrane asymmetry is maintained
-flippase
what does flippase do on the plasma membrane
-asymmetric lipid bilayer of plasma membrane
-delivery of new membrane by exocytosis
-flippase catalyses flipping of specific phospholipids to cytoplasmic monolayer
-flippase needs energy
how is the Negatively charged phospholipids in the cytosolic leaflet maintained
-Transfer of phosphatidylserine from the extracellular leaflet of the plasma membrane to the cytosolic leaflet
-have both scramblase and flippase at the plasma membrane
-The translocase transfers phosphatidylserine from the outer leaflet of the plasma membrane to the inner leaflet
-The scramblase abolishes asymmetry.
-The net equilibrium favours the translocase under normal conditions.
-causes Scotts disease- bleeding disorder
what % of our genome encodes for membrane proteins
-30%
- many are made in the ER
what do cels in our pancreas do
-secrete digestive enzymes, and they often secrete them in response to a signal.
what are the tubules of the ER constantly doing
-breaking and reforming
The endoplasmic reticulum structure
-The ER is connected to the nuclear envelope
-ER forms hollow tubes and flattened sacs. The chambers are cisternae
-Two types of ER
=Rough (RER) outer membrane covered in ribosomes
=Smooth (SER) no ribosomes
The endoplasmic reticulum functions
-Quality control
-Synthesis
-Storage
-Detoxification
why is the rough ER called that
-lots of ribosomes associated with it
what do chaperone proteins do
-help newly synthesised linear sequences of amino acids to fold correctly into tertiary and quaternary structures
structure and function of SER
-No ribosomes associated with the SER
-The SER is responsible for -
=Phospholipid and cholesterol synthesis
=Steroid hormone production
=Synthesis and storage of glycerides
=Synthesis and storage of glycogen
=Important role as a calcium store
-Functions: storage and detoxification
whats calcium signalling like in acinar cells
-zymogen granules contain enzymes important for digestion
-stimulation-> Ca2+ release from ER stores-> vesicle fusion-> enzyme release
what occurs in Transport from the ER to Golgi
-Transport between ER and Golgi in the form of vesicles and tubules
-The vesicles bud off the ER and are received by the Golgi
-Anything in the lumen or the membrane of the vesicle will be transported to the new compartment
what are vesicles coated with
-The area of membrane forming the vesicle is coated with a cage of specialised proteins
-The coat aids formation of the vesicle, but has to be discarded before the vesicle can fuse with the target compartment
-Three types of vesicle coat: Clathrin, COPI,COPII (last two are uncoated)
-COPII moves through the Golgi complex through to the plasma membrane
-COPI move material backwards and forwards through the Golgi complex
whats incorporated into coated vesicles
-cargo
-different types of coats that that characterise different transport carriers.
How do vesicles reach the correct target : Role of SNAREs
-SNARE - soluble N-ethylmaleimide-sensitive factor adaptor protein receptor
-Two types
=v-SNAREs : vesicle SNARES- found in the vesicle membrane.
=t-SNARE: target SNARES found in the membrane of the target membrane
-In nerve terminals, the SNARE complex involved in docking of synaptic vesicles is a helical bundle consisting of 3 components
structure of Golgi apparatus
-Golgi apparatus is composed of flattened discs – also called cisternae
-The cisternae communicate with the ER and cell membrane by use of vesicles and tubules
-Vesicles released from the ER bind to the cis face and are then processed and leave from the trans face of the organelle
what are the 3 primary functions of the Golgi
-Modification and packaging of secreted proteins
-Renewal and modification of the plasma membrane
-Delivery of material to other organelles, especially the endocytic pathway
what Trans-Golgi Network
-major sorting station for newly-made proteins
-From the Golgi to the plasma membrane
-Plasma membrane and secreted proteins are delivered to the cell surface by the constitutive secretory pathway in non-polarised cells.
1) signal-mediated diversion to lysosomes
2) signal-mediated diversion to secretly vesicles (from regulated secretion)
3) constitutive sensory pathway
