Plasma Membrane & Plant Cell Wall

where are peripheral proteins found

bound to membrane surface (on top of the lipid heads)

what function does asymmetry between leaflets in the plasma membrane serve?

electrochemical gradient --> important for signal transduction and transport of ions (negatively charged lipids on inner membrane)

what is lateral diffusion?

phospholipids on the same leaflet can switch places with each other (rarely flip flop between layers bc requires energy)

what are black membranes

planar lipid bilayers that form across a hole in partition b/w two aqueous places

main component of cell membrane

phospholipids and proteins

function of sterols

adds rigidity/stiffness to the membrane --> helps w/ structural integrity of plasma membrane warm temps: provides stiffness by preventing membrane from becoming too fluid low temps: keeps phospholipids from packing too tightly bc the sterols get in the way

what is pectin, where is it and what is its function

carbohydrates that form gel --> provide resistance to compression interwoven in cell wall w/ cellulose

what is the major component of the cell wall?

cellulose

what is the major sterol in animal cell membranes?

cholesterol

turgor pressure's role in cell development

driving force for cell expansion during growth

fluid mosaic model of plasma membrane

fluid: lateral diffusion of components in a leaflet mosaic: asymmetry, membrane is made up of clusters of diff types of molecules (discontinuous, not uniform)

what is the function of lignin

hard, waterproof filter --> cellulose is hydrophilic, would let water in

what is the only type of molecule that can pass thru the plasma membrane freely?

hydrophobic molecules

where are sterols located?

in between lipids in the bilayer

is the fluid mosaic model referring to an individual leaflet or the entire bilayer?

leaflet --> if you look down at the outer face of the membrane there are areas that are more abundant in one component than others ("neighborhoods")

which type of phospholipid is unique and why? (think charge)

phosphatidylserine has a net negative charge

lipid raft

low-density microdomains of plasma membrane rich in cholesterol and sphingolipids --> parts stick out far bc long tails so it looks like a raft NOT floating on the surface!

where are integral proteins found

membrane interior can span both leaflets in the transmembrane region could be anchored into 1 leaflet in b/w two lipids

what is the function of membrane proteins?

molecular transport, signal transduction, anchorage to cytoskeleton

can water pass thru cell membrane?

no --> it's polar so it can interact w the polar head of the phospholipid but it can't cross the inner region of hydrophobic tails

is energy needed for the membrane to self-assemble?

no additional energy input needed (assembly happens automatically)

can charged molecules or ions readily diffuse through the plasma membrane?

no bc charged molecules interact w polar regions (aka the phospholipid heads)

can glucose pass thru the membrane?

no because it has a lot of -OH groups which make it polar

is the plasma membrane symmetrical?

no; the inner and outer leaflets have diff distributions of types of phospholipids (this is not what the fluid mosaic model is referring to)

difference in charge between the leaflets

only the inner leaflet has negatively charged phospholipids

where is the plant cell wall located?

outside of plasma membrane of a plant cell (completely separate from plasma membrane)

Structure of a phospholipid

polar head group, 2 non-polar hydrocarbon tails -1 tail is saturated (no double bonds) so it's straight -1 tail is unsaturated (cis double bond) so it's bent

what properties of cellulose are important for cell wall?

provides tensile strength comparable to steel --> prevents cell from being stretched

what is the plasma membrane

regulated cell boundary: allows certain things to pass

structure of sterols

rigid ring structure polar head - fused rings - hydrocarbon tail

how does phospholipid structure affect fluidity of the membrane?

since one tail has cis double bonds, it is kinked --> phospholipids can't pack tightly --> increases fluidity

what are liposomes

spherical vesicles with a lipid bilayer --> spontaneous assembly

why does the bilayer form a sphere?

starts as planar but the non-polar tails on the edge interact w water (energetically unfavorable) --> folds into a sphere so that no tails are touching the water (energetically favorable)

turgor pressure

structural rigidity of cell wall allows for large internal pressure --> when cell has a lot of solutes, water flows in via osmosis

difference in symmetry b/w plasma membrane and ER membrane?

the plasma membrane is asymmetric; the ER membrane is symmetric

in what type of environment is turgor pressure highest?

when the extracellular environment is hypotonic

can membranes self-assemble and why?

yes bc of their amphiphilic nature --> polar heads associate w/ water, non-polar tails associate w/ each other on the inside

can steroids pass thru cell membrane?

yes because they are hydrophobic