Membranes and Protein Trafficking Part 2 PDF

Membranes and protein trafficking: Part 2 Secretory pathway & endocytic pathway Membranes and Protein trafficking– part 2 Secretory pathway & endocytic pathway LO: 1. Draw a basic diagram of the secretory pathway 2. Understand the role of secretary and endocytic vesicle...

Membranes and protein trafficking: Part 2 Secretory pathway & endocytic pathway Membranes and Protein trafficking– part 2 Secretory pathway & endocytic pathway LO: 1. Draw a basic diagram of the secretory pathway 2. Understand the role of secretary and endocytic vesicles 3. Be aware of mechanisms by which vesicles fuse with the correct targeted membranes Secretory pathway: Transport From the ER to Golgi to the Plasma membrane OVERVIEW OF THE SECRETORY PATHWAY. Transport between the three principal components of the secretory pathway: 1: The endoplasmic reticulum (ER), 2: Golgi apparatus 3: Plasma membrane. Cell Biology Figure 21.1  The secretory pathway This secretory pathway allows eukaryotic cells to (1) modify protein and lipid molecules (in the golgi) after their export from the ER (2) distribute proteins and lipids synthesized in the ER to the cell surface and other cellular sites (3) facilitate protein secretion  The secretory pathway deliver modified proteins to the cell surface The plasma membrane https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/plasma-membranes Secretory Transport From the Endoplasmic Reticulum to the Golgi Apparatus Transport of newly synthesized proteins out of the rough ER to the golgi takes place in specialized areas called ER export sites (ERES). This is called Anterograde transport Proteins of the Coat Protein Complex II (COPII) facilitate the formation of vesicles to transport cargo from the ER to the Golgi apparatus COPI mediated Golgi to ER transport is called retrograde transport  Rough ER and Golgi transport Retrograde transport VTC/ COPII-coated vesicles fuse with the VTC in close proximity to ER export sites. VTCs also act as recycling stations from which retrograde COPI vesicles can return proteins to the ER. The remaining membranes travel as transport containers along Anterograde transport https://en.wikipedia.org/wiki/Vesicular-tubular_cluster microtubules to the Golgi complex where they form new cis golgi cisternae. Membrane phosphoinositides are important in defining organelle identity The secretory pathway Cell Biology Figure 21.1 Membrane phosphoinositides are important in defining organelle identity The main constituents of membrane bilayers are Phosphoglycerides (also called glycerophospholipids) The alcohol head groups give phosphoglycerides their names: phosphatidic acid [PA] (no head group) phosphatidylglycerol [PG] (glycerol head group) phosphatidylethanolamine [PE] (ethanolamine head group) phosphatidylcholine [PC] (choline head group) phosphatidylserine [PS] (serine head group) phosphatidylinositol [PI] (inositol head group) Cell Biology Figure 13.2  Membrane phosphoinositides are important in defining organelle identity https://emr.wicmb.cornell.edu/phosphoinositide-lipid-signaling/ https://www.nature.com/articles/s41418-018-0269-2 GA = Golgi Apparatus, SV = secretory vesicles, MVB = multivesicular bodies, L = lysosomes, NCE = clathrin-independent endocytosis, CE = clathrin- PI(3)P = PIP PI(4,5)P2 = PIP2 dependent endocytosis, EE = early endosomes, RE = recycling endosome Tethering factors target carrier vesicles to specific organelles Cell Biology Figure 21.13 SNARE proteins target vesicles to specific destinations and facilitate membrane fusion V-Snare T-Snare Cell Biology Figure 21.14 The Golgi apparatus is a protein-sorting station for the delivery to many cellular destinations. This includes transport to the plasma membrane, secretion to the cell exterior, sorting to the endosome/lysosomal system, or retrieval back to the ER. Specific V-snares on the vesicles provide the postcode and Specific T-Snares on target membranes are the “mail box” motor proteins attach to cargo-filled vesicles and carry them along the Cell Biology Figure 21.23 cytoskeleton like trucks on a highway Exocytosis: fusion of secretory vesicles with the plasma membrane https://www.thoughtco.com/what-is-exocytosis The Endocytic pathway (substances are brought into the cell) Cell Biology Figure 22.1 PHAGOCYTOSIS OF A BACTERIUM BY IMMUNE CELL Cell Biology Figure 22.3  Endocytic pathways Cell Biology Figure 22.4 CONTENT SORTING ALONG THE ENDOCYTIC PATHWAY Internalising and recycling of surface receptors 1: Cargo and membrane taken up by clathrin-mediated endocytosis are delivered to early endosomes, which mature into multivesicular bodies and late endosome before fusion with lysosomes. 2: Each compartment sorts membrane containing receptors that are recycled to the plasma membrane either directly or indirectly through perinuclear recycling endosomes or the trans-Golgi network (TGN).