Membrane Structure and Transport Flashcards
solvent
water the universal solvent for biological solutions
solutes
Sugars, proteins, electrolytes, and organic molecules like hormones are examples of the different biological solutes dissolved in water.
Hydrophobic nature is one of the factors that holds the plasma membrane together in this aqueous environment and allows the membrane to perform one of its primary functions—to be a selectively permeable barrier
plasma membrane
primarily composed of lipids, making it hydrophobic.
selectively permeable
- some substances may freely cross the membrane
- others require assistance to cross
- some substances are not able to cross at all
cholesterol
- rigid ring lipid
- randomly distributed throughout hydrophobic region
- gives plasma membrane structural strength
carbohydrate chains
- extend from outer surface
- attached to protein or phospholipid
- functions as a signal, coating, or receptor
extracellular environment
- outside of cell
- aqueous
lipid bilayer
- composed of two rows of phospholipid molecules
- phosphate group head faces outward
- fatty acid tails face inward
phosphate group head
- part of phospholipid molecule
- contains a phosphate group
- makes this portion of molecule polar and hydrophilic
fatty acid tails
- part of phospholipid molecule
- tails consist of two fatty acid chains
- makes this portion of molecule nonpolar and hyrophobic
peripheral protein
- does not extend across lipid bilayer
- may server as an anchor point for cytoskeleton
transmembrane proteins
- extends all the way through the lipid bilayer
- may serve as a transport protein or a channel across the bilayer
cytoplasm
- inside of the cell
- aqueous
- contains organlelles
passive transport
- occurs down the gradient and does not use ATP
- includes simple diffusion, osmosis, facilitated diffusion
active transport
- occurs against gradient and requires ATP
- includes primary active transport, secondary active transport, receptor-mediated transport, phagocytosis, and pinocytosis
simple diffusion
- driven by the concentration or pressure gradient
- may occur through different media
- may or may not include semipermeable membrane
- gas exchange in lungs or dye spreading through liquid
facilitated diffusion
- solute particles move down the gradient
- involves carrier proteins (transporters) in the cell membrane
- glucose transporters across the membrane (GluT)
osmosis
- solvent moves down the concentration
- involves semipermeable membrane
- movement of water from hypotonic to hypertonic compartment
primary active transport
- moves the substance against the chemical/electrical gradient
- involves direct use of ATP
- Na+/K+ ATPase pump moves K+ into and Na+ out of the cell
secondary active transport
- moves the substance against the gradient
- is driven by primary active transport
- no direct use of ATP
- sodium-dependent glucose transporter (SGLT) moves glucose into cell along with Na+
receptor-mediated transport
involves membrane surface receptors to internalize the substance
phagocytosis
cells ingulf solid particles or bacteria or etc
pinocytosis
cells engulf liquid substance
diffusion
- high concentration → low concentration
- passive
- driving force is random collision or kinetic energy
simple diffusion
- water
- oxygen
- steroid hormones
^ all freely move across the cell membrane
facilitated diffusion
- ions
- glucose
- amino acids
^ need assistance of a channel/transport protein to cross the cell membrane
osmosis
- special case of diffusion
- needs selectively permeable membrane (passable to solvent but impassable to solute)
hypotonic solution
- named for lower solute concentration
- hypo mess less than
- higher water (solvent) concentration
- net movement of water out of this side
hypertonic solution
- higher solute concentration
- hyper means greater than
- lower water (solvent) concentration
- net movement of water towards this side
selectively permeable membrane
- water (solvent) freely passes through
- solute molecules cannot pass through
isotonic solution
- iso means the same
- equal solute and solvent concentration on both sides of the selectively permeable membrane
- water molecules continue to cross the membrane but no net movement
with time, water moves down the gradient
- from hypotonic solution
- toward hypertonic solution
- goal is to reach equilibrium
Osmotic pressure
the pressure generated within a cell as water presses against the plasma membrane
isotonic solution for RBC
- equal solute concentration on both sides of the membrane’
- no concentration gradient
- no net movement of water
- no change in RBC shape
hypotonic solution for RBC
- smaller solute concentration outside membrane
- concentration gradient exists
- net flow of water INTO the RBC
- RBC swells and may lyse (burst)
hypertonic solution in RBC
- greater solute concentration outside membrane
- concentration gradient exists
- net flow of water OUT of RBC
- RBC crenates (shrink)
