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cell membranes
cell membrane structure and function
| Question | Answer |
|---|---|
| Selective permeability | allows some substances to cross more easily than others |
| Amphipathic molecule | has both hydrophilic and hydrophobic regions |
| Fluid Mosaic Model | cell membrane is a fluid structure with a “mosaic” of various proteins embedded in or attached to a bilayer of phospholipids |
| 2 major membrane proteins | integral proteins and peripheral proteins |
| Integral proteins | penetrate the hydrophobic core of the lipid bilayer. The hydrophobic regions consist of nonpolar amino acids coiled into alpha helices. The hydrophilic parts are exposed to the aqueous solution on either side of the membrane. |
| Transmembrane proteins | span the cell membrane |
| Peripheral proteins | appendages loosely bound to surface of cell membrane (they are not embedded in the lipid bilayer), often exposed to parts of integral proteins |
| 6 major functions of membrane proteins | transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attachment to cytoskeleton and ECM |
| glycolipids | carbohydrates covalently bonded to lipids |
| glycoproteins | carbohydrates covalently bonded to proteins |
| transport protein | a transmembrance protein that helps a certain substance(s) cross the membrane |
| 2 types of transport proteins | channel proteins & carrier proteins |
| channel protein | transport protein with a hydrophilic channel for certain molecules/ions; eg, aquaporins |
| aquaporins | a channel protein that allows rapid entry of water molecules through the cell membrane |
| carrier protein | transport protein that holds onto their passengers and change shape in a way that shuttles them across the membrane |
| what properties allow O2 and CO2 to cross lipid bilayer without help from membrane proteins? | size & polarity: they are both small and nonpolar |
| why would water molecules need a transport protein to move rapidly and in large quantities across a membrane? | water is polar so cannot pass rapidly through the hydrophobic region of the phospholipid bilayer |
| on which side of the vesicle membrane are carbohydrates (that are added to some proteins/lipids to be added to plasma membrane) attached? | the inner side of the transport vesicle membrane |
| diffusion | movement of molecules of any substance so they spread out evenly into available space (from area of high to low concentration) |
| concentration gradient | a region along wich the density of a chemical substance increases or decreases |
| passive transport | diffusion across a membrane in which no energy is required |
| osmosis | diffusion of water a cross a selectively permeable membrane |
| tonicity | the ability of a solution to cause a cell to gain or lose H2O. depends on the concentation of solutes that can’t pass the membrane (nonpenetrating solutes) |
| animal cell in hypotonic soln | swells and bursts. More relative H2O outside cell >>> water moves into cell. |
| Plant cell in hypotonic soln | normal/turgid (very firm), water pushes against cell wall |
| Anima cell in isotonic soln | stays the same |
| Plant cell in isotonic | flaccid (limp) |
| Animal cell in hypertonic soln | shrivels up. less relative H2O outside cell >>> water leaves cell into soln |
| Plant cell in hypertonic soln | plasmolyzed (plasma membrane pulls away from cell wall, causes plant to wilt) |
| Osmoregulation | control of h2o balance |
| Facilitated diffusion | diffusion with the help of transport proteins (ie, channel proteins or carrier proteins) |
| 2 types of channel proteins | water channels (aquaporins) and ion/gated channels |
| gated channels | open or close in response to chemical or electrical stimulus |
| how does a cell performing cellular respiration rid itself of the resulting CO2? | CO2 is small and nonpolar and can diffuse through membrane along the concentration gradient. |
| Why do vegetables sprayed with h2o at the supermarket look crisp? | the h2o is hypotonic to the plant cells so they take up the water, making the cells turgid |
| Active transport | pumping a solute across a membrane against the concentration gradient, requires energy expenditure |
| Sodium-potassium pump | pumps 3Na+ outside of cell and takes 2K+ in |
| Membrane potential | the voltage across a membrane, ranges from –50 to –20 mV |
| Electrochemical gradient | the combination of forces (electrical and chemical) acting on an ion |
Created by:
jondoh
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