BIOL10004 Chapter Notes - Chapter 4: Globular Protein, Organelle, Metaphase

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29 Jun 2018
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Eukaryotes II
Endoplasmic reticulum
Endoplasmic reticulum (ER) network of membranous sacs (cisternae)
Extends throughout cytoplasm of eukaryotic cells
Continuous with outer membrane of nuclear envelope
Cisternae flat and sheet-like
Often linked by tubular cisternae
Forms continuous membrane system enclosing cisternal space
Occupies small cell volume, ER surface-to-volume ratio is huge
Forms direct connections between adjacent cells
Passes through center of pore-like plasmodesmata between cells
Most ER in cells are Rough Endoplasmic Reticulum which have ribosomes bound to the
surface
oGives "rough" appearance
oRibosomes involved in protein synthesis
oIncorporated into membranes
oSecreted at cell surface or transported into vacuoles or lysosomes
oPolypeptides pass into lumen of rough ER
oInside protein folding assisted by binding protein (BiP)
o3-D structure stabilized by protein disulfide isomerase
Catalyses formation of disulphide bonds between cysteine residues in the
protein sequence
oLumen of ER, proteins glycosylated through addition of carbohydrate chains
Smooth Endoplasmic Reticulum
oLacks attached ribosomes
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oRough + smooth ER can synthesis lipids
oSpecialized cells producing large amounts of lipids have more Smooth ER
oER manufactures most phospholipids and cholesterol needed for membrane repair
oContains enzymes responsible for detoxifying lipid-soluble drugs + metabolic waste
Rough + smooth ER perform different functions
Must maintain regions that have different molecular compositions
Golgi Apparatus
Consists stacks of 4-10 disc-shaped cisternae
1-2 micrometers in diameter
Flat or curved cisternae
Each stack surrounded by clouds of small vesicles
Golgi stacks have distinct polarity
Cis face (entry face)
oLacks ribosomes
oCytosol between ER cisterna and face filled with small vesicles that are 50nm
Trans face (exit face)
oAssociated with system of tubular membranes
Proteins and glycoproteins enter by cis face
Transferred from ER in vesicles and fuse with the cis cisterna
Progression through stack proteins + glycoproteins modified
oN-linked glycoproteins trimmed/ sugar added to core
oo-linked glycoproteins produced in Golgi apparatus from proteins containing serine,
threonine or hydroxyproline
oSugars added to hydroxyl groups of side chains on amino acids
Model 1
oCargo molecules move
oOne cisterna to the next via small vesicles
oProcessing enzymes modify cargo molecules remain in same cisterna
Model 2
oCargo molecules entered cis-most cisterna
oRemain in cisterna and progress through the stack
oProcessing enzymes moved indirection from one cisterna via small vesicle
oOnce mature products reach trans face
oSorted and targeted to correct destinations
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Intracellular sorting and transport
Golgi apparatus processes large number of products
Must be packaged and transported
Some are enzymes for degradative processes
Some are glycoproteins or polysaccharides for export across plasma membrane
Vesicle formation
oMaterials sorted and distributed
oSorting of proteins
oTrans-Golgi network lumen with 'cargo' receptors on inside face of membrane
oVesicle marker (v-SNARE) marks different types of vesicles
oFormation of vesicles aide by binding of scaffolding proteins to patches of
membrane
oClathrin
oCOP1
oCOP2
oCoated vesicles pinched off, coat proteins dissociate
oExposes v-SNARE marker
oProteins interact and fuse with target docking (t-SNARE) proteins on target
membrane
Each coated vesicle functions in movement of material between compartments in the cell
COP2 vesicles mediate anterograde transport from ER to cis-face of Golgi
COP1 vesicles mediate retrograde transport between cisternae within Golgi stack
oCis-Golgi cisternae to ER
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Document Summary

Endoplasmic reticulum (er) network of membranous sacs (cisternae) Continuous with outer membrane of nuclear envelope. Forms continuous membrane system enclosing cisternal space. Occupies small cell volume, er surface-to-volume ratio is huge. Passes through center of pore-like plasmodesmata between cells. Most er in cells are rough endoplasmic reticulum which have ribosomes bound to the surface: gives rough appearance o o o o o o. Secreted at cell surface or transported into vacuoles or lysosomes. Inside protein folding assisted by binding protein (bip) Catalyses formation of disulphide bonds between cysteine residues in the protein sequence o. Lumen of er, proteins glycosylated through addition of carbohydrate chains. Lacks attached ribosomes o o o o o. Specialized cells producing large amounts of lipids have more smooth er. Er manufactures most phospholipids and cholesterol needed for membrane repair. Contains enzymes responsible for detoxifying lipid-soluble drugs + metabolic waste. Rough + smooth er perform different functions. Must maintain regions that have different molecular compositions.

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