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What are lipids (definition)?
catch all term for carbon containing compounds that are found in organisms and are largely nonpolar and hydrophobic (do not dissolve in water)
hydrocarbon chains without double bonds (straight) saturated with maximum number of hydrogen atoms that can attract
has double bond (bent), fewer than maximum number of hydrogen’s are attached
What is membrane permeability? What factor effect permeability?
- Permeability = tendency to allow a given substance to pass through it. Membrane have polar, hydrophilic region
- Number of double bonds in hydrophobic tail, overall length, number of cholesterol molecules nearby
- Lipid bilayers containing many unsaturated fatty acids have more gaps and should be more permeable than bilayers with few unsaturated fatty acids
- More permeable with short, unsaturated hydrocarbon tails. Long strait saturated fatty acid tails less permeable
- Adding cholesterol molecules to liposomes dramatically reduces the permeability of the lipid bilayers
- Low temperatures lower permeability, molecules in bilayer move more slowly, pack together, begin to solidify
spontaneous movement of a substance from a region of high concentration to one of low concentration, down concentration gradient
diffusion of water across a selectively permeable membrane from a region of high concentration (low solute concentration) to a region of low water concentration (high solute concentration)
Can you look at a molecule and know its likely permeability?
- Small, nonpolar molecules move across bilayers quickly. Large molecules and charged substances cross membrane slowly, if at all.
- Charged compounds and large, polar molecules cant pass through the nonpolar, hydrophobic tails of a lipid bilayer
- solution has a greater solute concentration and lower water concentration
- Cell shrink and membrane shrivel
- solution that has lower solute concentration, higher water concentration
- Cell will swell or burst
- concentrations equal on either side of the membrane
- Does not affect membrane’s shape
Integral membrane proteins
any membrane protein that spans the entire lipid bilayer (transmembrane protein)
Peripheral membrane proteins
does not span the entire lipid bilayer and associates with only one side of the bilayer (attached to transmembrane)
aby membrane protein that enables a specific ion or small molecule to cross a plasma membrane. Includes carrier proteins and channel proteins, which carry out passive transport (facilitated diffusion), and pumps, which carry out active transport.
type of channel protein that allows certain ions to diffuse across a plasma membrane down an electochemica gradient
forms a pore in a cell membrane. Structure of most allows them to admit just one or a few types of ions or molecules
allow water to cross the plasma membrane over 10 times faster without
(transporters) – membrane protein that facilitates diffusion of a small molecule (glucose) across the plasma membrane by a process involving a reversible change in the shape of the protein (facilitated diffusion)
membrane protein that can hydrolyze ATP to power active transport of a specific ion or small molecule across a plasma membrane against its electrochemical gradient (sodium-potassium pump) 3 NA/ 2 K