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what are three classes of lipids?
phospholipids, glycolipids, cholesterol
what are the components of phospholipids?
two chains of fatty acids, glycerol, phosphate and alcohol
what are the different types of alcohols of phospholipids?
serine, glycerol, inositol, ethanolamine, choline; phosphatidylcholine
what are fatty acids?
carboxylic acids that have long hydrocarbon chain (pamitate, and oleate)
what is a sphingomyelin?
another type of phospholipid without a glycerol backbone, based on the structure of sphingosine
what are glycolipids?
- contain sugars, based on structure of sphingosine
- fatty acid connected via the amino group
when phospholipids are placed in solution?
there are no covalent interactions, stabilized by ionic interaction with polar heads and hydrophobic interactions with fatty acid tails
what binds the integral and peripheral membrane proteins?
- integral proteins bound by hydrophobic interactions (they themselves are hydrophoblic and are helical)
- peripheral proteins bound by electrostatic and hydrogen binding interactions
what determines the ability of the molecule to pass through the biological membrane?
ability is governed by thermodynamics (diffusion from high to low conc)
how do hydrophillic molecules get through membrane?
- active transport (use ATP hydrolysis to overcome thermodynamic barrier)
- secondary active: use energy of binding of small molecules, do not require ATP hydrolysis
- passive: holes that allow diffusion of molecules, can be very specific due to their structure
what does the P-type ATPase transporters often involve?
an enzyme intermediate in which the pohospate from ATP is transferred to a specific Asp residue on the protein forming a phosporylaspartate intermediate
what is the relative concentration of Na and K inside the cell vs outside?
high concentration of K and low concentration of Na inside cell
what is secondary active transporters?
they couple flow of one molecule in the thermodynamically favorable direction with another molecule int he thermodynamically unfavorable direction
what kind of a transporter is lactose permease and when is it used?
when levels of glucose are low and lactose is high in media, lactose permease protein is epxressed, moves to the membrane and allows higher levels of lactose to enter the cell usiing the H+gradient to provide the thermodynamic driving force for the transport of lactose
describe the structure of the K+channel
tetramer of identical subunits; pore is water fileld
how is the selectivity for potassium come about?
- five amino acids stretch in channel acts as the selectivity filter (thr-val-gly-tyr-gly)
- selectivity is related to the free energy cost of hydration of the ions; side chains in the protein are setup so when a water interaction is lost with K+ it is replaced by a backbone hydrogen bond interaction with the protein
describe the model for K+ channel?
- four binding sites of K+ in the channel
- after two K+ enter channel, charge charge repulsion pushes them apart
- as more K+ enter channel there is more repulsion and K is forced out to the exterior