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describe the membrane system.
- plasma membrane and membrane of organelles
- all has common structure: lipid and protein molecules held by noncovalent interactions
- dynamic fluid structures; many molecules can move in and out of plane
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Describe the lipid bilayer.
- double layer lipid about 5 nm thick
- almost all lipids are amphipathic with hydrophilic polar end and hydrophobic non-polar end
- most lipids are phospholipids
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cholesterol and glycoplipids are found on membranes. What are they?
- cholesterol makes membrane more rigid
- glycolipids (lipids with attached sugar residues)
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biological membranes differe in their _______ and ____ composition.
lipid and protein
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What are the jobs of protein on membrane?
- transport of ions and polar molecules
- binding of hormones and cytokines
- signal transduction across the membrane
- and structural stabilization of the lipid bilayer.
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Ratio of protein:lipid determine their _____. Ex. myelin sheath...
- function
- myelin sheath with very low protein:lipid ratio
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What are transmembrane proteins?
- extend through the lipid bilayer
- has both hydrophilic and phobic regions
- another name = integral proteins
- pass thru membrane once (growth factor receptors) or many times (transporters and membrane channels)
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what are surface proteins?
- covalently attached to the lipid bilayer
- have post-translational modifications such as fatty acids, prenyl groups or oligosaccharides that attach to the protein to the surface
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what are Peripheral proteins?
bound to the membrane by noncovalent interactions with other membrane proteins.
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what is the function of plasma membrane?
- encloses the cell, defines its boundary, and maintains the essential differences between the cytoplasm and extracellular environment.
- transducing signals and the transport of metabolites between the intra- and extra-cellular compartments.
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Describe ER and what is the function?
- branching tubules and sacs that extends throughout
- all interconnect to form a continuous sheet enclosing an internal space - ER lumen
- ~50% of the total area
- biosynthetic processes
- rought ER: with ribosomes, synthesis of membrane and secretory proteins
- smooth ER: membrane lipid biogenesis
- ex. improper folding proteins = toxic effects = liver damage in antitrypsin deficiency
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describe golgi apparatus and its function.
- flattened, stacked membranes or sacs (cisternae)
- modification, packing and sorting of macromolecules for secretion and delivery to other organelles
- receives lipids and proteins from the ER and sends them to a variety of destinations
- covalently modifying them (e.g. glycosylation, phosphorylation) along the way.
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