Cell And Molecular Biology Flashcards
What is the process of endocytosing LDLs from the bloodstream?
Recognition of packaged LDL by receptors -> R recruiting clathrin coat by mediators eg adductin -> dynein cleaves off vesicle by GTP hydrolysis -> clathry coat dissembled -> fusion to endocytic vesicle then endosome -> acidification and dissociation of receptor -> Rs recycled -> fusion to lysosome -> LDL gedraded by lipidases -> cholesterol secreted
What are the names of the different clathryn-like proteins and where are they localised?
Clathryn - plansma membrane, early endosomes, endocytosis, trans Golgi
COPI - Golgi apparatus
COPII - sER
What is the involvement of the sER in vesicle transport?
SER prepares lipids to be inserted into membranes by joining two fatty acids with a phosphate group in one of the doible membrane layers.
This is where prots synthetised in the rER are packaged and released
What are the different versions of vesicular transport and what are they used for?
Phagocytosis: actin mediated vesicle formation usually around a foreign body to internalise it for degradation in the lysosome, useful proteins and sugars extracted are recycled
Autophagy: malfunctioning own components are surrounded by small vesicles and engulfed, delivered to lysosome for degradation eg mitochondria, components recycled
Exocytosis: release of proteins, neurotransmitters or mucus from the producing cells
Describe SNARE-mediated vesicle fusion!
Direct fusion impossible bc of slight negative charge of serines
T and v-SNAREs facilitatee fusion by forming a coiled coil structure zipping the vesicle to the membrane with their hydrophobicity (2 snare pairs per vesicle)
In the space between the SNARE pairs, the membrane is forced to mingle and content can be released
SNAREs are separated then recycled
( in NT uptake, the vesicle gains a v-SNARE as a process of recycling)
How is vesicular secretion regulated? What types are there?
Constituitive release: contents are secreted as they are made by simple diffusion of the vesicle to the membrane
Good for eg mucus release in the lung
Regulated secretion: contents are packaged and highly concentrated by the removal of excess lipid packaging when samller vesicles form (insulin creates crystals this way) vesicles wait closely related to the plasma membrane for a signal when to be released
Eg insulin and other enzymes that are only periodically needed.
What are the key locations of protein traficking?
RER, sER, Golgi apparatus, secretory vesicles
What processes are performed withing the rER?
Proteins are sythetised into this space if their mRNA has the right localisation sequence by SRP. SRP is recognised by SRP-R, which recruits a translocator prot. The prot is threaded into the ER as it is made on the ribosome. A cleavage protein cuts the signal sequence off and the prot is released. Transmem prot have a stop threading signal= hydrophobic aa sequence.
What happens to proteins in the sER
Protein modifications, such as the addittion of a GPI anchor to the prot to keep it anchored to the membrane. The correct folding is also ensured
Cisteines are able to form sulphide double bonds since the enviro is not reducing like the cytosol
What happens to proteins in the Golgi apparatus?
Mainly sortinga nd editing. Proteins that have afunction in the ER are transferred back.
Aspartime chains are added to proteins as a quality control tag (no degradation)
Glycocalyx is built up (imp for neuronal myelin)
Separate cisternae keep prots apart that could interact with each other.
[eg Band3 prot on RBC: one sugar manipulated for diff blood types]
What happens to proteins in teh secretory vesicles?
Enzyme trimming and maturation: Cleavage of pro-protein forms [pre usually removed in Golgi already] Eg insulin Differential cleavage from a shared pro-from to obtain several different end products.
