Vesicular Transport PDF

VESICULAR TRANSPORT Monday, September 25, 2023 4:17 PM Continued membrane transport: assisted membrane transport VESICULAR TRASNPORT → For large polar molecules and multi-molecular materials to enter and leave the cell ○ Ex: protein hormones secreted by endocrine cells ○ Ex: ba...

VESICULAR TRANSPORT Monday, September 25, 2023 4:17 PM Continued membrane transport: assisted membrane transport VESICULAR TRASNPORT → For large polar molecules and multi-molecular materials to enter and leave the cell ○ Ex: protein hormones secreted by endocrine cells ○ Ex: bacteria ingested by white blood cells → Non-polar molecules can cross the membrane no problem REMINDER: → Requires energy expenditure by the cell -> active mechanism of transport - lysosomes contain ○ This energy is needed to accomplish vesicle formation and movement within the cell hydrolytic enzyme ○ No gradient involved → Two forms of active transport: 1. Endocytosis ( cell going inside ): three forms depending on the material internalized Pinocytosis Fuses with lysosome (in rare Receptor-mediated endocytosis instances -> bypasses lysosome -> Phagocytosis exocytosis from other end) 2. Exocytosis ( when cell is releasing a vesicle ) ENDOCYTOSIS: pinocytosis → Pinocytosis (nonselective uptake of a sample of ECF) = cell drinking ○ Specialized cells will drink fluid around them, doesn't matter what is being consumed ○ As they sample the fluid, they form a membrane and take it inside the cell → Micropinocytosis = large gulps of fluid ( this is how dendritic cells take up foreign material to activate the immune system) ADDITIONAL NOTES: - Dendritic cells sit in our tissue and non specifically drink large amounts of fluid from around them - They look for pathogens - Sit in our liver, skin, lungs, gut ENDOCYTOSIS: receptor-mediated endocytosis → Uses receptors with ligase that are selective ○ Ex: insulin, iron, vitamin B12 uptake → Vesicles can't form without the receptor engaging its lagan → Once it does bind it forms a vesicle and the receptor will send signals to the cell to begin endocytosis ADDITIONAL NOTES: - Viruses can use this mechanism to enter the cell ENDOCYTOSIS: phagocytosis → Phagocytosis: selective uptake of a multimolecular particle = cell eating → Only phagocytes can do phagocytosis which are all immune cells → Their job is to eat its prey ( a pathogen or bacterium ) → During the course of the immune response: ○ Macrophages are like phagocytes that start eating the cells ○ Will coat the pathogen with our own protein to allow phagocytes to use receptor mediated phagocytosis EXOCYTOSIS → Almost the reverse of endocytosis (NO FUSION WITH LYSOSOMES ) → Two purposes: ○ Secretion of large polar molecules (i.e., hormones or enzymes) ○ Addition of components to membrane (i.e., channels or receptors) Sometimes nothing is leaving the cell Sometimes the cell wants to send one of those membrane proteins How it's done is the substance or material is put into a vesicle and once it fuses with the membrane it won't be released but stuck to the vesicle due to its design to be bind to the membrane → This is when a cell has made a vesicle and its secreting outside the cell → Vesicle is being made in the Golgi → Does not fuse with lysosomes → All exocytic vesicles becomes part of the membrane whether its contents are going to be released into the ECF or remain part of the membrane ○ The collection of vesicles wont cause the cell to get bigger bc endocytosis will counter it, when contents come through the membrane endocytosis will use the vesicles already on the membrane EXCOSYTOSIS AND SECRETORY VESICLES Picture description: The green and purple barrier around the vesicles are proteins Green = v-snare / docking marker - it’s a protein that binds to docking marker acceptors which is found on the intracellular side of the cell - V stands for vesicle T-snare - Stands for target - Is found on the membrane BALANCE OF ENDOCYTOSIS AND EXOCYTOSIS → This Is what keeps the cell shape more or less the same → Rate of processes are regulated to maintain a constant membrane surface area and cell volume (> 100% of plasma membrane can be used in an hour to wrap internalized vesicles!!!) → Membrane is constantly restored, retrieved -> recycled → Cells are differentially selective in what enters and leaves