Lipids, Membranes and Cell Topology Flashcards
Lipid bilayer
arrangement of phospholipids where the polar heads are exposed to water and fatty acid tails are sandwiched in the middle, this arrangement causes membrane to be selectively permeable and assemble spontaneously
Phospholipid composition
head group and phosphate group attached to 3 carbon glycerol backbone with two fatty acid tails attached to 2 carbons of the glycerol backbone
head group
polar- hydrophilic
unsaturated fatty acid tail
hydrophobic, with one or more double bonds (causes kinks in the molecule)
saturated fatty acid tail
hydrophobic, no double bonds so no kinks
cholesterol
another component of the lipid bilayer, stabilizes phospholipids by filling in gaps, making it rigid and less fluid, also amphipathic, acts as a membrane fluidity “buffer” so although when there is already more molecular space the addition of cholesterol makes it less fluid, when the membrane starts out more packed together the addition of cholesterol makes it more fluid.
amphipathic molecule
molecule that has both hydrophobic and hydrophilic parts
selective permeability
some molecules can freely diffuse across membranes and other molecules cannot, allows for cellular compartmentalization
freely permeable
hydrophobic molecules (O2, CO2, N2)
slightly permeable
small, uncharged polar molecules (H2O, glycerol)
impermeable
large, uncharged polar molecules (glucose, sucrose) (due to hydrophobic center), ions (H+, Na+)
spontaneous assembly
how phospholipids assemble into lipid bilayer formation using no energy, does not defy the 2nd law of thermodynamics
second law of thermodynamics
entropy can only increase so in spontaneous assembly, even though the phospholipids become more ordered, the water molecules become more disordered so the net entropy is actually increases
hydrophobic effect
liquid water alone is highly disordered, but water forms cages around hydrophobic molecules (ex. tails of phospholipids) which is unfavorable for H2O entropy, this causes the phospholipids to orient themselves with their hydrophobic tails facing each so the H2O molecules are shielded from the tails and so the H2O can return to its naturally disordered state
non-covalent bonds and strengths
ionic (electrostatic)>hydrogen bonds>Van der Waals (transient, fluctuating charges)
“fluid mosaic” model for cellular membranes
the fluid refers to how cell membranes are 2-d fluids (phospholipids have movement- lateral diffusion, flexion and rotation) and mosaic refers to how membranes are made up of lots of different molecules
fluorescence recovery after photobleaching (FRAP)
refers to bleaching fluorescent phospholipids or other structures, if the dark spot caused by bleaching becomes fluorescent again, it indicates fluidity
regulation of membrane fluidity
less molecular space (longer straight phospholipid tails) makes membranes less fluid while more molecular space (shorter tails with kinks) means more fluid; in the example, bacterium adjusts lipids in its membrane to create more fluidity in the new temperature
cell topology
the way in which the parts of a cell are arranged relative to one another, as organized by membranes
topology of the eukaryotic cell
the cytosol and nucleus are “topologically equivalent” because the nuclear pore complex creates an open channel between the two, however, the ER is “topologically distinct” from the nucleus and cytosol because it is separated by two membranes from those areas
why would the pH of the cytosol and nucleus always be the same?
The pH of the cytosol and nucleus must be the same because protons (H+) would be able to diffuse freely through the aqueous pores that connect these topologically equivalent compartments.
