Eukaryotic Test Lecture 1

• 1. Membranes arise only from preexisting membranes
• 2. Newly synthesized proteins and lipids are inserted into existing membranes in the ER and modified by enzymes residing in the cell's various organelles

Maintained as membrane carriers bud from one compartment and fuse to the next

• ERGIC: Endoplasmic Reticulum Golgi Intermediate Compartment
• VTC's: Vesicular-tubular carriers
• --After budding from ER membrane, transport vesicles fuse w/one another to form larger vesicles and interconnected tubules in the ERGIC

• Found by Camillo Golgi in 1898 by application of metallic stain to nerve cells
• Morphology: Flattened, disklike, membranous cisternae w/dilated rims and associated vesicles and tubules
• Typically FEWER THAN 8 cisternae are arranged in an orderly stack

CGN (ENTRY FACE): Sorting station distinguishing between proteins to be shipped back to the ER and those going to next Golgi station

TGN (EXIT FACE): Sorting station in which proteins are segregated into different types of vesicles either to the PM or to various intracellular destinations

• 1. Synthesis of the N-linked core oligosaccharide is initiated in the ER and finished in the Golgi complex
• 2. O-linked oligosaccharides are assembled in the Golgi complex
• 3. Synthesis of most of a cell's complex polysaccharides, including glycosaminoglycan chains of proteoglycan and the pectins and hemicellulose in plant cell walls
• 4. A single core oligosaccharide is assembled in the ER, whereas carbohydrate domains produced in the Golgi complex are quite different

The sequence of the sugars incorporated into oligosaccharides is determined by the spatial arrangenment of the specific glycosyltransferases

• Cisternal Maturation Model: Golgi cisternea formed at cis face of the stack by fusion of membranous carriers from the ER and ERGIC . Each cisterna "mature" into the next cisterna along the stack
• Vesicular Transport Model (false model): Cisterna remain stable, cargo is shuttled thru golgi stack from CGN to the TGN in vesicles that bud from 1 membrane compartment and fuse w/neighboring compartment along the stack

Protein Coat: Soluble proteins that assemble on the cytosolic surface of the donor membrane at sites where budding takes place

• 1. Mechanical device causing membrane to curve and form budding vesicles
• 2. Mechanism for selecting components to be carried by vesicle
• a. cargo consisting of secretory, lysosomal, and membrane proteins to be transported
• b. The machinery required to target and dock the vesicle to the correct acceptor membrane

COPII: Move materials from ER forward to the ERGIC and golgi complex

• COPI: Move materials inretrograde direction
• 1. From ERGIC and golgi stack backward to ER
• 2. From trans golgi cisternae backward to cis golgi cisternae

Clathrin: Move materials from TGN to endosomes, lysosomes, and plant vacuoles & from PM to cytoplasmic compartments during endocytosis

Integral proteins captured by COPII contain ER export signals at cytosolic tail & interact specifically w/ COPII proteins

• 1. Enzymes that act at later stage in biosynthetic pathway
• 2. membrane proteins involved in docking & fusionof vesicles w/target compartmetn
• 3. membrane proteins that are able to bind soluble cargo

sar1 is a small GTP-binding protein, regulating assembly and disassembly of vesicle coat

• Proteins are maintained in an organelle by a combo of:
• 1. Retention: molecules are excluded from transport vesicles
• 2. Retrieval of "escaped" molecules back

Retrieval signal: a short AA sequence at C-terminus of ER resident proteins. KDEL for soluble proteins of lumen & KKXX for membrane proteins

• 1. 2-step addition of phosphate group to certain mannose sugars of the N-linked oligosaccharides
• 2. Phosphorylated mannose residues function as recognition signals
• 3. Mannose-6-phosphate signals are recognized by mannose-6-phosphate receptors (MPRs)
• 4. MPRs are connected to clathrin molecules thru GGA adaptors
• 5. formation of clathrin-coated vesicles initiated by small GTP-binding protein, ARF1

• 1. Movement of vesicle toward specific target compartment
• 2. Tethering vesicles to the target compartment
• 3. Docking vesicles to the target compartment
• 4. Fusion between vesicle and target membrane

The fusion of a secretory vesicle or secretory granule w/the PM and subsequent discharge of its contents

Generally triggered by an in increase in Calcium (Ca2+) concentration