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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
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
cholesterol and glycoplipids are found on membranes. What are they?
- cholesterol makes membrane more rigid
- glycolipids (lipids with attached sugar residues)
biological membranes differe in their _______ and ____ composition.
lipid and protein
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.
Ratio of protein:lipid determine their _____. Ex. myelin sheath...
- myelin sheath with very low protein:lipid ratio
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)
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
what are Peripheral proteins?
bound to the membrane by noncovalent interactions with other membrane proteins.
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.
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
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.