biological membranes Flashcards
what are FA composed of?
long chains of hydrocarbon carboxylic acids
-up to 24C long
-general formula CH3(CH2)nCOO-
what conformation are most naturally occuring double bonds in?
cis
what does each number of the short hand notation for naming FA represent?
the first number is the number of carbons, the second number is the number of double bonds
-the number beside the delta sign indicates what carbon the double bond is at
what affect does increasing the number of carbons have on the MP of FA?
increasing chain length will increase MP
what affect does increasing the number of double bonds have on the MP of FA?
increasing the number of double bonds will decrease the MP
what 2 factors affect FA MP?
length and unsaturation
does unsaturation or chain length have a greater effect on FA MP?
unsaturation
what is the packing structure of saturated vs unsaturated FA?
saturated FA pack closely together while unsaturated FA cannot pack closely due to a bend in their chain
How are fatty acids stored?
Triacylglycerol (TAG) is a way of storing FA
-very hydrophobic (not amphipathic)
-three acyl chains attached to glycerol
what is the most common form of triacylglycerols (TAG)?
mixed TAGs
-triacylglycerol with more than one different FA
How does melting point differ depending on saturation and chain size?
MP is lower for TAGs containing unsaturated FA or shorter chains
what lipids make up membranes?
glycerolphospholipids, sphingolipids and cholesterol
are glycerophospholipids amphipathic, polar or hydrophobic?
amphipathic
what makes glycerophospholipids similar to triacylglycerol?
it has a fatty acyl group covalently attached
what are chemical properties of cholesterol?
mostly hydrophobic
-rigid, non-polar and weakly amphipathic (1 OH group)
can cholesterol form a membrane on it’s own? what is its function?
no it cannot form membranes alone, the OH associates with polar headgroups of other lipids and non-polar portion found inside membrane
-cholesterol is needed in order to maintain membrane fluidity and rigidity
what occurs to amphipathic molecules in water? what do lipids form? what do FA form?
they form micelles or bilayers
-lipids form a bilayer
-FA form micelles
why do amphipathic molecules form bilayers or micelles in water?
this arrangement eliminates unfavourable contact between water and hydrophobic tails while permitting solvation of polar head groups
what can lipid bilayers form?
spherical vesicles (liposomes)
what is the composition of lipid bilayers?
changes depending on lipid composition but it non-covalently assmebles and contains:
-acyl chain
-polar head group
what factors contribute to a thicker lipid membrane?
more carbons/larger heads = thicker membrane
what occurs to lipid bilayers when they are below transition T?
acyl chains pack together in a gel-like solid state
what occurs to lipid bilayers when they are above transition T?
acyl chains move freely and rapidly
why does cholesterol work to increases membrane rigidity?
because it is rigid and planar it is able to limit rotational movement of neighboring acyl tails—> increasing van der waal interactions
in what way are lipids able to move within a bilayer?
they move freely and rapidly by lateral diffusion
are lipids able to undergo transverse diffusion?
a significant energy barrier prevents transverse diffusion at appreciable rates
-flipases increase rate of transverse diffusion
what kinds of membrane proteins are there?
integral, peripheral and lipid-linked
what kinds of AA side chains would you expect to see on the portion of an integral membrane protein that interacts with the acyl tails?
hydrophobic side chains
are regular structures able to cross membranes?
yes, alpha-helices and beta-sheets are both able to cross membranes
what kind of transport do proteins adhere to within the membranes?
lateral movement
-cannot easily undergo transverse movement
what kinds of molecules are able to cross the lipid bilayer by simple diffusion?
small, non-polar molecules
what does the rate of simple, unmedieated diffusion depend on?
-size of molecule (smaller move faster)
-[gradient]; larger gradient increases diffusion
-lipid solubility (greater solubility increases diffusion rate)
what type of transport do porins and ion channels enable?
passive transport via membrane-spanning pores
are ion channels selective or non-selective?
they are highly selective
are porins selective or non-selective?
they are non-selective
what is the structure of a porin?
trimers with water-filled pore in the center
how does a transporter protein differ from a transport protein?
transporter proteins are carrier proteins and they do not have membrane-spanning pores
-they have conformational changes
-selective of substrate
-can be passive or active
what kind of kinetic curve would you expect to see for passive transport by carrier proteins?
hyperbolic
summarize the 4 ways a substrate can be transported across a membrane
1) simple diffusion
2) passive, channel mediated transport
3) passive, carrier mediated transport (transporter)
4) active, carrier mediated transport (transporter)
what are the 3 classifications of transporter proteins in terms of how they transport?
uniport - one molecule one direction
symport - 2 of the same molecules in the same direction
antiport- 2 different molecules in different directions
what is the difference between primary and secondary active transport?
primary uses a direct source of ATP while secondary uses an ion gradient created from primary transport
what are the steps required for the Na+/K+ ATPase?
1) 3 Na+ molecules bind
2) ATP binds and a phosphoryl group is transferred to the side chain of the pump and ADP is released
3) A conformational change occurs expelling Na+ to extracellular space
4) 2 K+ molecules bond and the side group containing P is hydrolyzed to release inorganic phosphate
5) this causes a conformatinoal change and K+ is released into the cell
where is the [glucose] higher in the Na+ glucose transporter system? what is the delta G for this transport?
[glucose] inside the cell > [glucose] outside the cell
delta G > 0 for the transport of glucose inside the cell
-going against [gradient]
where is the [Na+] higher in the Na+ glucose transporter system? what is the delta G for this transport?
[Na+] inside the cell < [Na+] outside the cell
delta G is < 0 for the transport of Na+ into the cells
-going with [gradient]
how is glucose able to enter the cell if the delta G for the Na+/glucose transport system is > 0?
The transport of Na+ provides energy for glucose import into the cell
