ch. 11 cell bio flashcards

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what kind of barriers are cell membranes, difference in bacterial vs. eukaryotic

selective - only let through specific molecules
bacteria - single membrane
eukaryotic - internal membrane for organelles separate from plasma membrane

3 roles of membrane

communication (receiving info with receptors)
import/export (move molecules w/ channels/pumps)
growth/movement (cytoskeleton, adding new membrane)

why are membranes compartmentalized?

allows chemical rxns (and organelles) to be separate
protects vital structure (DNA)

hydrophilic vs. hydrophobic

hydrophilic: dissolve in water, charged or polar
hydrophobic: insoluble in water, uncharged + nonpolar

most common phospholipid in cell membrane + composition of hydrophilic head

phosphatidylcholine,
choline, phosphate, glycerol

fat molecules vs. phospholipids

fat molecules are hydrophobic
phospholipids are both amphipathic + hydrophobic

properties of phospholipid bilayers

spontaneously close to go from energetically unfavorable → favorable, form sealed compartment, important for creation of living cell

liposomes

pure phospholipids added to water
create drug delivery vesicles, important for pharmacies + drugs research

flip-flop

lipid movement, move from 1 end to another + requires energy + enzyme (flippase), rarely happens,

lateral diffusion

side-to-side movement, moving around + going past ppl in a line

rotation

spinning in a circle

flexion

moving legs while stationary (more bent)
hydrocarbon tail = legs

2 properties of hydrocarbon tails that affect how tightly they’re packed in bilayer

length: short = dec. tail interaction + inc. fluidity
# of double bonds: more difficult to pack together, more double bonds = more fluidity

what does cholesterol do to membrane

stiffens bilayer in animals @ room temp = more rigid + less permeable
short + rigid = fills space btwn adjacent phospholipid molecules left by kinks

functions of lipid bilayer on each side

asymmetrical
red = phosphatidylcholine: structural, found on outside
brown = sphingomyelin: myelin sheathing, found on outside, cell signaling cascade
gray: cholesterol: maintain fluidity + structure of membrane

bilayer synthesis

new membrane synthesis - occurs in ER
new membranes exported to other membranes in vesicles by budding + fusion

flippases

catalyze transfer of phospholipid molecules to opposite monolayer, preserve orientation
keep cytosolic surface facing cytosol + noncytosolic surface away from cytosol

membrane proteins mass

50% of mass of most plasma membranes

transmembrane proteins

amphipathic
interior: hydrophobic
exterior: hydrophilic

monolayer membrane proteins

amphipathic, a-helix exposed on surface of protein, outer part

lipid-linked membrane proteins

lie entirely outside on bilayer on cytosolic/extracellular side
attached by 1 or more covalently-bound lipid groups

protein-attached membrane proteins

bound indirectly by weak, non-covalent interactions w/ other membrane proteins
1 or the other face membrane
all except these are integral membrane proteins

what affects how polypeptide chain crosses bilayer as a-helix

hydrophobicity
a-helix has outer hydrophobic amino acids that attract them to hydrocarbon tails on membrane
peptide bonds are polar → hydrophilic

how are transmembrane proteins related to cell signaling

act as receptors to relay signals from extracellular environment to cell

detergents

destroy lipid bilayer + allowing release of membrane proteins
are amphipathic, disrupt hydrophobic associations

cell cortex

meshwork of fibrous proteins that’s attached to cytosolic face of membrane
reinforces + supports cell membrane

spectrin

main component of cortex for red blood cells
provides support for plasma membrane + maintaining cell’s shape
most simple + researched
spectrin mutations = anemia

spectrin linking to membrane

intracellular attachment proteins link spectrin to specific transmembrane proteins

membrane domains

functionally specialized regions on cell or organelle surface
how cells confine plasma membrane proteins to local areas within bilayer and still let them float around

4 ways protein movement is restricted in membrane

1. tether to cell cortex inside cell

2. extracellular matrix molecules outside cell

3. tether to proteins from another cell

4. diffusion barriers restrict protein to specific domain

carbohydrate layer

majority of plasma membrane proteins have short sugar chains linked to them (oligosaccharides)
forms sugar coating = carb layer
proteoglycans (heavily glycosylated) attach to glycosaminoglycans (GAGs), provide filler btwn cells

function of carb layer

protect cell surface from mechanical + chemical dmg
absorb water = slimy feeling: helps motility + prevents cells sticking tg
cell-cell recognition + adhesion