Cell membranes Flashcards
function of membrane proteins
Signaling, protection, structure and movement, transport and general homeostasis
3 components of a lipid (glycerophosholipids)
- fatty acid tail
- ~16-18 carbon (even #), unbranched, saturated or unsaturated - glycerol backbone
- ester linkage to fatty acid tails - phosphate head
-“R” is linked (ester) to another molecule
-choline, ethanol amine, glycerol, inositol, serine
i.e. phosphatidylcholine (PC) and phosphatidylethanolamine (PE)
what is cholesterol? where is it found? what does it do to cell membranes?
-type of steroid
-intercalates between phospholipid with the OH- closest to the aqueous interface
-small amounts = decrease fluidity, “Stiff”
-large amounts= increase fluidity, interfere with interactions between lipid tails
sphingolipids; components; cellular function, what structure it contributes to
-sphingosine backbone, NOT glycerol like other lipids therefore membrane fluidity is decreased
-sugar residues with many functions
–> cellular functioning: form lipid rafts and myelin
–> contribute to glycocalyx which signal to other cells
“Sphingosine is formed by an amino alcohol head group, with two hydroxyls, and one amino group attached to a long unsaturated hydrocarbon chain of typically 18 carbon atoms”
in sphingolipids the glycerol component is replaced by a long-chain amino alcohol known as sphingosine, which is amide-linked to a fatty acid and phosphate group
types of sphingolipids
ceramide
sphingomyelin
cerebroside
ganglioside
what is the bond between a fatty acid tail and the glycerol backbone
ester linkage
what can sphingolipids form?
lipid rafts and myelin
what is a glycocalyx
-glycocalyx signal to other cells
-they are proteins (glycoproteins) and lipids that are bound to carbohydrates that vary in size
-outer leaflet of the cell; protect structure and singaling functions
-sphingolipids contribute to them
membrane lipids characteristics
-amphipathic- micelle or phospholipid bilayer
–> both thermodynamically favourable (i.e. hydrophilic head in aqueous environment on outside)
-increase [ ] of phospholipids then bilayer formation more favourable then micelles
what membrane lipids inside the cell dont need to do
-membrane lipids inside the cell dont need to:
-signal to other cells
-protect cells from harsh environments or microbes
-form a glyocalyx
–> therefore dont need sphingolipids
-less cholesterol in membrane of organelles
–> Golgi or smooth ER might have more cholesterol and sphingolipids because they are made or modified there
diffusion
diffusion: high to low [ ], spread out molecules; spontaneous (Gibbs)
osmosis
osmosis: water diffuses through semi-permeable membrane (allows water to pass through, but is impermeable to at least 1 solute)
i.e. if add sugar to a semipermeable system then water will go to where sugar [ ] is higher to balance it out
what are membrane lipids a barrier to?
-charged and polar molecules
-medium and large non polar molecules
integrity of membrane via membrane lipids
-ionic and fluid homeostasis, cell movement, and shape
-less integrity = threaten cell survival
membrane permeability and concentration gradients and osmosis
-cell membranes are semi-permeable
-aquaporins in plasma membrane –> high water conductance
-membranes impermeable to larger solutes
-interior of cell has high [ ] of large solutes therefore must expend energy to regulate solute concentration and cell volume
–> concentration gradients