Exam 4 Flashcards
Vesicle Transport
The ER and Golgi package materials in vesicles for transport
Pathway of vesicle formation and fusion
Vesicle with protein coat on outside buds off of ER membrane at donor compartment with specific molecules for transport bound to transmembrane receptors. Protein coat is mostly removed, and vesicle fuses with the target site.
Vesicle coat proteins types and function
COPII is used for forward movement of vesicles from ER to ERGIC to Golgi, out
COPI is used for reverse flow vesicle movement in ER resident proteins, Golgi to ER, uses Sar 1-GDP, Sec23 and Sec24
Clatherin is used in forward and backward movement from the Golgi to PM, secreted, endosome, lysosome, general export from golgi to final destination, uses Arf1-GDP, GGA, and AP1
Formation of Clatherin
Arf1-GDP binds to cytoplasmic side of Golgi membrane and uses a GEF to replace GDP with GTP
Arf1-GTP binds to adaptor protein GGA, also on cytoplasmic side of membrane
GGA binds to receptor in Golgi membrane, receptor binds to specific material to be transported
Adaptor protein AP1 binds to the receptor on cytoplasmic side of Golgi membrane
Clatherin binds to AP1 and bends the membrane to break it into a vesicle.
Specific cargo binds to specific receptors in the Golgi
Vesicle Fusion
Rab GTP attached to vesicle is tethered to Rab Effector on the target organelle or destination
vSNARE on vesicle protein and tSNARE on target area coil around each other to cause the vesicle to fuse membranes
Transport materials are released into target area
SNAREs are disassembled with accessory proteins NSF and SNAPs
Vesicles/Proteins destinations from trans golgi
Secreted(growth factor and hormones), PM(RTK, GPCR, Na/K pump), Endosome, Lysosome, back to ER
Constitutive secretory pathway of vesicles
vesicles leave trans Golgi and fuse immediately, unregulated
Regulated secretory pathway
vesicles move to PM and waits to fuse until a signal such as hormone or neurotransmitter activates it
Lysosomes structure
Organelle containing mainly hydrolytic enzymes, used to break down molecules, all 4 major groups. Glycosidases break down carbs. Function at optimal 5 pH, so enzymes are denatured if they leave lysosome to more basic cytosol. Contains integral membrane protein that pumps H+ ions into lysosomes.
Lysosomes function
Digests molecules engulfed in endocytosis and phagocytosis by binding to them. Also digests cellular components in autophagy if components are malfunctioning or during starvation of nutrients. Lysosomes lacking their enzymes can lead to build up of molecules in storage, unable to break them down.
Receptor mediated endocytosis
Molecules like LDL bind to receptors in the outer PM and then form a vesicle that will be sent to the lysosome. Receptors can be recycled.
Endosome
Vesicle compartment with a membrane, involved in sorting, transport, and recycling components. Endocytic vesicles move to the early endosome, where the receptors and transport material is separated. Receptors are sent to the recycling endosome, where they are move to the PM. Materials move to the lysosome for digestion. Errors with endosomes can lead to problems with recycling receptors, and ultimately buildup of materials. Artherosclerosis, buildup of LDL in arteries causing clogging, is caused by problems with the endosome.
Protein processing in the Golgi, to the PM or secreted
Glycoproteins going to PM or to be secreted are modified by the Golgi via adding and removing sugar from Olig. Sach. Glycosyltransferases are enzymes that add monosaccharides to oligosacc. Glycosidases are enzymes that remove sugars from oligosacc.
Protein processing in Golgi, to lysosome or endosome
Glycoproteins to the lysosome and endosome have phosphate, mannose, added to create Mannose-6-Phosphate M6P. To go to lysosome, M6P is required AND SIGNAL PATCH IS REQUIRED, signal patch is a protein folding modification
Lipid modifications in the Golgi
Ceramide is made in the smooth ER, hydrophobic, nonpolar tail, hydrophilic, polar head. Ceramide can have phosphorylcholine, named because of Phosphate group added to ceramide, Sphingomyelin is created, in the lumen side of the Golgi. Glycolipids can also be made by adding sugar residue to ceramide, on the cytoplasmic side of the Golgi.
Glycolipids pathway after made
Ceramide added with sugar residue creates glycolipids, enzyme flippase transversely moves it from cytoplasmic side to lumen side of Golgi. Needs to be moved into lumen to be placed in a vesicle, vesicle fuses to PM, where the glycolipid is facing outside of its cell and used as a tag for cell to cell recognition.
Disassembly of SNAREs
Disassembly of SNARES require proteins NSF and SNAPs, SNARE accessory proteins
Cytoskeleton Filament classes and structure
Microfilaments are 7nm diameter, made of actin. Intermediate Filaments 8-10nm diameter, made of mixture with lamin proteins and others
Microtubules are 25nm in diameter, made of tubulin
Cytoskeleton Function for cell shape
Maintains cell structure, Including cell cortex that uses MFs to modulate the cell shape.
Includes Permanent extensions like cilia, flagella that use MTs, microvilli on the digestive tract uses permanent MF extensions. Transient extensions include filopodia(spiked), lamellipodia(web of extensions), pseudopodia(ring shaped for phagocytosis).
Cytoskeleton Function in locomotion of cells
Cells need to be moved in unicellular organisms and in motile cells in multicellular organism in cases of development and cancer metastasis. Extensions of cytoskeleton aid movement.
Cytoskeleton Function in intracellular movement
Cytoskeletal fibers guide vesicle movement throughout the cell to their destination. MTs in the cytoskeleton pull apart chromosomes. MFs form the contractile ring during mitosis, and are used in the contraction of muscles.
Microfilament Protein, Actin
Makes up 5-10% of protein in cells. Minus - Pointed end and Plus + divot barbed end, structurally polar. Monomer is G actin, Polymer Rod structure is known as F actin.
Assembly/Disassembly of Actin Polymer
G actin is dimerized, then trimerized in Actin Nucleation. More monomers begin to add to the trimer to make F actin in Actin Polymerization. G actin monomers with ATP add to the Plus + Barbed Divot end of the polymer. The G actin is hydrolyzed once in the middle of the polymer, now has ADP. Monomers with ADP are removed from the negative - end as new ones with ATP are added to + end.
Actin Treadmilling and Size management
Treadmilling is adding Ga to the plus end and removing it from the minus end, adding towards the desired direction, maintaining constant length of filament. Requires critical concentration of G-actin with ATP. If above critical concentration, the filament will grow, and if below crit. concentration, the filament will shrink. Moves in equilibrium with polymerization and depolymerization. Used in cell migration and shape change.
Actin Binding Proteins ABPs
ABPs regulate polymerization of actin.
Alpha-Actinin - forms a dimer with 2 total ABPs, forms contractile bundles by holding filaments
Alpha-catenin - Binds to B-catenin to form adherins junctions(cell to cell connection with microfilaments), connecting to contractile bundles at ALPHA in cytoskeleton and cadherins at BETA(with p120).
Ankyrin - anchor protein that binds to spectrin and Band 3 in erythrocytes
Arp 2/3 - used in nucleation, polymerization of Branched MFs. Located on MINUS end of actin MF, creating a branch and eventually transient extensions
Cadherin - binds MFs together. Creates adherins junction, is a transmembrane glycoprotein, binds to itself in ECM and B catenin, p120
Cofilin - binds to G-a-ADP, preventing exchange of ATP and shrinking MF
Filamin - V shaped dimer with 2 ABDs, helps hold MF networks together, flexibly
Fimbrin - used in tight packing of parallel bundles, used in extensions
Formin - Dimer that slides along + end of actin MF, making linear and unbranched F actin used in extensions
Integrin - transmembrane protein that interacts with the ECM to form focal adhesions(cytoskeleton connecting to ECM). Binds to talin and vinculin, which are bound to MF
Profilin - Stimulates G-actin ATP exchange, growing MF.
Protein 4.1 - Cytoplasmic protein that binds to glycophorins(transmembrane glycoprotein) as an intermediate to the MF
Severin - severs MF into fragments
Spectrin - Tetramer with 2 ABDs in erythrocytes that holds MF structure along with Band 3 and Ankyrin.
Talin - binds to integrin in focal adhesions, along with vinculin
Vinculin - binds to talin and integrin, Foc. Adh.
Myosin, Classes
Molecular motor protein, converts ATP or chemical energy into mechanical energy to contract muscles. Myosin is used in cytokinesis and mitosis as well.
Class one is conventional myosin, includes Myosin type II.
Class two include unconventional myosins like Myosin I.
