chapter 12 Flashcards
membranes are how thick
2 molecules thick
membranes are composed of
lipids and proteins
membrane lipids are
small amphipathic molecules that form closed bimolecular sheets
membrane proteins serve to
mitigate the impermeability or membranes and allow movement of molecules and information
membranes are….. (noncovalent or covalent)
noncovalent
membranes are (symmetric or asymmetric)
asymmetric (outside is always different than inside)
membranes are (nonfluid or fluid)
fluid duh
how are membranes formed
phospholipids spontaneously form lipid bilayers in aqueous solution (because the head is hydrophilic and the tail is hydrophobic) and then van der waals stabilize the membrane
membranes have _____ permeability for ions and polar molecules
LOW
what is melting temperature
temperature at which a membrane transitions from being highly ordered to very fluid
the melting temperature is dependent on what
the length of the fatty acids in the membrane lipid and the degree of cis unsaturation
what does cholesterol do
maintain proper membrane fluidity in membranes of animals
integral proteins
embedded in the hydrocarbon core of the membrane
peripheral proteins
bound to the polar head groups of membrane lipids or to the exposed surfaces of integral membrane proteins
membrane spanning a helices
integral membrane proteins
bateriorhodopsin (light powered protein pump)
porin
B strands that form a pore in the membrane
porin is an example
inside is polar and filled with water
fluid mosaic model
describes membranes as two dimensional solutions of oriented lipids and globular proteins
lateral diffusion
very fast
transverse diffusion
very slow
lipophilic molecules pass through how
down their concentration gradients in the process of simple diffusion
passive transport
movement (facilitated diffusion) by charged molecules down their concentration gradient
active transport
molecule movement across a membrane against concentration gradient that requires energy
atp driven pumps
lipid fluidity independent
carriers
lipid fluidity dependent
channels
lipid fluidity independent
Na-K pump or Na-K ATPase
P-type ATPase
goes from low concentration to a high concentration
most animal cells have a high concentration of K and a low concentration of Na relative to the external environment - this pump maintains and generates this gradient
what are the 2 conformations of p-type atpase pumps
1: ion binding site facing into the cell
2: ion binding site facing out of the cell
what powers the interconversion between the two conformations of p-type atpases
ATP hydrolysis
multi-drug resistance protein
atp-dependent pump that extrudes small molecules from the cell
member of ABC transporter family
what characterizes ABC transporters
common domain called ATP-binding cassette (ABC)
ABC transporters consist of
two ABC domains and two membrane spanning domains (4 in total)
what is the difference between MDR (multidrug resistance protein) and MsbA (bacterial lipid transporter)
MDR domains are linked together and are 1 peptide chain with chains linking all domains together
MsbA does dimerization and the dimers are not linked together
what is a carrier
protein that transports ions or molecules across the membrane WITHOUT ATP hydrolysis
how do carriers transport
facilitated diffusion - high to low concentration
secondary active transport - low to high concentration by using energy of another gradient
what do symporters do
power the transport of a molecule against its concentration gradient by coupling the movement to the movement of another molecule down its concentration gradient, with both molecules moving in the same direction
what do symporters do for dummies
the molecule going high to low concentration piggy backs on the molecule going low to high concentration and goes with the flow (cheating the system)
the molecules are moving in the SAME (sym) direction
what do antiporters do
use one concentration gradient to power the formation of another but the molecules move in the OPPOSITE direction
what do uniporters do
transport a molecule in either direction depending on the concentration difference across the membrane
what are channel proteins
channels in the membrane for molecules to pass through
how are channel proteins selective
there are 2 sections to the channel - a larger channel and a smaller channel
molecules that are just right are the perfect size for both and can pass through both “filters” in the channel without blocking
what accounts for the rapid rate of transport in potassium ion channels
charge repulsion among the 4 binding sites
