Membranes Flashcards
cell membrane: general features
- selectively permeable
- fluid mosaic
- protects the cell
- bind to cytoplasm and extracellular matrix
- controls content of cytoplasm
- sense molecules and other cells in the environment
lipids: general features
- diverse class biological molecules
- don’t mix well with water
- non polar
- fats, phospholipids, steroids
- hydrophobic
- consist of hydrocarbons
phospholipids: features
- most abundant lipid in plasma membrane
- amphipathic (has both hydrophobic and hydrophilic regions)
- 2 fatty acids (tail) + phosphate group attached to glycerol (head)
micelles:
- small objects forming naturally
- hydrophobic tails point inwards
- aid in transport and absorption of complex lipids and fat soluble vitamins (vit A)
fluid mosaic model:
- membrane is a fluid structure with mosaic of various proteins embedded in it
- phospholipids in plasma membrane can move around in bilayer
- about as fluid as salad oil
significance: cholesterol in warm/cool temps
- controls fluidity of membranes
- 37˚ restrains movement of phospholipids
- cool temp: prevents tight packing
Frye and Edidin’s experiment:
- membrane fusion
- human and mouse membrane proteins labelled with fluorescent antibodies
- proteins intermixed
carbohydrates found:
- exterior of membrane
significance: ER and Golgi apparatus in building membrane
- determines asymmetrical distribution of proteins, lipids, associated carbohydrates in plasma membrane
molecules which pass through membrane easily:
- gases (CO2, N2, O2)
- water
- small, uncharged nonpolar molecules (urea, ethanol)
molecules which pass through membrane difficultly:
- charged polar molecules (amino acids, ATP)
- ions (K+, Mg2+, Ca2+, HCO3-, H2PO4)
- large uncharged nonpolar molecules (glucose)
list membrane proteins:
- peripheral
- integral
- transmembrane
peripheral protein:
- bound to surface f membrane
integral protein: what type
- penetrate hydrophobic core
- amphipathic
transmembrane protein:
- integral proteins which span membrane
membrane proteins: types
- transport
- structural
- enzymes
- cell-to-cell interaction proteins
- cell communication
hydrophobic domains in transmembrane proteins region of integral protein:
- stabilise it within lipid bilayer
list six major functions of membrane proteins:
- transport
- enzyme activity
- signal transduction
- cell-cell recognition
- intercellular joining
- attachement to cytoskeleton and extracellular matrix (ECM)
osmosis:
- diffusion of water across selectively permeable membrane
- moving from low solute conc. to higher
hypotonic:
- lower solute conc. than intracellular fluid
- lysed (burst)
isotonic:
- same solute conc. as intracellular fluid
hypertonic:
- higher solute conc. compare to intracellular fluid (shrivelled)
diffusion:
- small substances spread out evenly into available space
facilitated diffusion:
- transport proteins speed up passive movement of molecule across plasma membrane
- channel proteins (ion channels) open/close responding to stimulus (gated channels)
transport protein: and eg.
- allow passage of hydrophilic substances across membrane
- channel proteins: tunnel
- carrier proteins: bind to molecules and change shape to shuttle them across membrane
- specific to substance it moves
list types of transport proteins:
- uniport
- co-transport (symport, antiport)
uniport:
- single substance moved in single direction
co-transport:
symport: 2 different substanced moved together same direction
antiport: 2 substances in both directions
significance: aquaporins
- normally lipid bilayer blocks/ slows flow of polar molecules (water)
- aquaporins membrane channels allow water to cross cell membrane
gated channels: trigger eg.
- some need to be triggered
- absence of acetylcholine, ion channel is closed
- if acetylcholine binds to receptor, channel opens
active transport: eg
- requires energy ATP
- sodium potassium pump
membrane potential:
- voltage difference across a membrane
how is voltage created: and electrochemical gradient
- differences in distribution of positive/negative ions
two combined forces drive diffusion of ions across a membrane:
- chemical force (ionic conc. gradient)
- electrical force (effect of membrane potential on ionic movement)
how ion pumps maintain membrane potential:
- electrogenic pump (transport protein) generates voltage across membrane
- animal: sodium potassium pump
- plants/bacteria/fungi: proton pump
sodium potassium pump:
- active transport
- 3 sodium leave cell, 2 potassium enter
- 3 NA bind to pump (cytoplasmic side)
- ATP hydrolysis phosphorylates pump -> releases NA
- 2 K bind on extracellular side
- phosphate group released -> allow K in
