Cell Membrane Overview Flashcards
what intermolecular force drives the formation when phospholipids are added to water?
driven by an increase in entropy. lipids cause water to arrange into an ordered, unfavorable cage-like structure (called a Cathrate cage). forcing lipids into a bilayer reduces this effect
phospholipids, cholesterol, and temperature
closer they pack, less fluid.
at low temperatures, they are packed closely together. cholesterol inserts in the hydrophobic region, seperating lipids and decreasing the strength of VDW forces (increasing fluidity)
at high temperatures, cholesterol forces lipids to become closer to each other, decreasing fluidity
paw of a polar bear contains saturated/unsaturated phospholipids
something that increases fluidity
unsaturated, because they must remain fluid to be functional at low temperatures
high temperatures require what kind of bilayer?
something that decreases fluidity
- saturated lipids have more VDW interaction and decrease fluidity
- longer tails have more VDW and decrease fluidity
how does glucose enter the cell?
facilitated diffusion through a carrier protein
facilitated diffusion
does not require ATP, limited by the number of proteins on the surface of the cell
which type of membrane protein is most likely a hormone?
peripheral protein (which include peptide hormones)
steroid is not a membrane protein
integral protein cannot leave the cell membrane and would be a terrible signaling protein
lipid-bound proteins remain in the phospholipid bilayer by the fatty acid tails, so they would also be terrible signal proteins
peptide hormones interact with the integral proteins in cell receptors.
peptide hormones include…
insulin. growth hormone.
rate of osmosis across a cell membrane depends on…`
- presence of aquaporins
- intracellular and extracellular solute concentrations
does NOT depend on polarity or molecular weight of solutes
osmotic pressure is a colligative property (dependent on the ratio of solute to solvent, not the identity of the solute or solvent)
aquaporins
channel proteins that allow water to flow through a cell membrane
what is the purpose of K+ and Na+ pumps across a channel? (in a nerve cell)
to store electrical and chemical energy (which can be used in action potentials)
during action potential
Na+ and K+ move across the membrane through sodium and potassium channels (NOT pumps)
action potential = channel
sodium-potassium pumps
increase Na+ outside the cell, and K+ inside the cell
Na outside (Na, I'm outside) K inside (special K cereal is inside the house)
cell membranes defined by
semi-permeability
phospholipids (parts)
- phosphate head
- glycerol backbone (hold it together)
- fatty acid tails
is both hydrophilic and phobic (amphiphathic)
passive diffusion
small, nonpolar molecules (like gases)
small polar molecules (water, ethanol) move slowly
large non-polar molecules move slowly
glucose is/is not polar
is polar (see the OH groups)
the diversity of phospholipids
serine, choline, ethanolamine, inositol, and glycerol bonded to the phosphate by phosphoester bond
what makes up the cell membrane?
phospholipids, cholesterol, proteins
cholesterol
4 rings, rather stable structure. maintain the fluidity of a cell membrane (keeps it fluid in low and high temperatures)
proteins in cell membrane
integral (transmembrane) protein
act as receptors and transportation
glycoproteins
carbohydrates bound to proteins (or glycolipids) which play a big role in communication (allows cells to recognize other cells), can be found in any proteins
fluid mosaic model
a fluid membrane (discovered in 1972)
two types of integral proteins
channel protein (hole inside) lets Na+ pass, or flow, through (won’t on its own), from high to low concentration (does not require energy)
carrier protein: carries a substance (like a glove) and can act against a concentratin gradient
types of proteins found in membrane
peripheral, integral, lipid-bound, channel, carrier
“PLICC” membrane
membrane fluidity affected by…
- temperature
- cholesterol
- saturated/unsaturated
low temperatures
form a crystalized state, lower fluidity
high temperatures
more fluidity, increased distance between PL
cholesterol on fluidity (very interesting)
increases distance between PL at low temperature
decreases distance between PL at high temperature
saturation on fluidity
high saturation, reduced fluidity
the bent, unsaturated are more fluid
