sides of plasma membrane for epithelial transport
apical (top; where substances enter the cell)
basolateral (bottom; where substances leave the cell)
what makes up plasma membranes?
phospholipid bilayer
cholesterol
proteins
functions of the plasma membrane
helps maintain the composition of intra- and extracellular fluids
regulates traffic into and out of the cell
forms the framework for protein components
detects chemical messengers arriving at the cell surface
links adjacent cells together
desmosome
extension of the plasma membrane that acts as an anchor, preventing cells from falling apart
its environment is very hydrophobic
tight junction
allows water or other aqueous molecules to pass through
also holds cells together
gap juction
specialized protein complex that creates an aqueous pore between two adjacent cells
typically involves ion movement
simple diffusion
movement of molecules from an area of high concentration to an area of low concentration
is gradual, passive, and creates a uniform distribution
does NOT stop when equilibrium is reached (but net flux = 0)
substances diffuses down its own concentration gradient
flux
measure of the rate of diffusion
factors of net flux
concentration gradient
temperature
surface area
permeability
what is the ranking of the relative permeability of molecules (most to least)?
hydrophobic molecules
small, uncharged polar molecules
lage, uncharged polar molecules
ions
what is the most hydrophilic molecules?
water
what molecules are mediated transport systems needed for?
molecules too large or polar to diffuse
types of mediated transport
facilitated diffusion
active transport
bulk transport
facilitated diffusion
mode of transport where a protein allows an otherwise impermeable molecule to cross a membrane down its concentration gradient
channel
corridor for charged molecules to pass through a plasma membrane
specificity depends on charge and pore size
osmosis
net diffusion of water from a region of high concentration to a region of low concentration
its direction is determined by difference of solute concentration, NOT the type of solute
osmolarity
total concentration of solutes in a solution
conditions of osmolarity
isosmotic
hyposmotic
hyperosmotic
isosmotic
cell has an equivalent osmolarity to its extracellular environment
aims to be maintained in physiological conditions
hyposmotic
cell has a lower osmolarity than its extracellular environment
hyperosmotic
cell has a higher osmolarity than its extracellular environment
gated channels
channels that require a certain stimulus to open
types of gated channels
ligand-gated, voltage-gated, mechanically gated
ligand gated channel
ligand binds to the receptor-channel -> regulates the opening and closing of the gate
voltage gated channel
regulated by the electrical state of the cell
mechanically gated channel
regulated by physical changes to the cell
characteristics of protein carriers
specificity
saturation
competiton
competition
molecules with similar chemical structures compete for carrier binding sites
passive mediated transport
no ATP is required
involves permease as the carrier protein
active mediated transport
requires ATP (directly -> primary; indirectly -> secondary) does NOT depend on the concentration gradient critical for a cell to maintain its internal concentrations of small molecules that would otherwise diffuse across the membrane
primary active transport
requires ATP
moves solutes against their concentration gradients
involves specific membrane-bound transport proteins
calcium ion pump
ATP hydrolysis is required
causes a higher concentration of calcium ions outside the cell, and a lower concentration inside the cell
sodium/potassium pump
requires ATP hydrolysis
causes an increase of potassium ions inside the cell, and an increase of sodium ions outside the cell
facilitates many biological functions
function of a steep gradient
involved in electrochemical impulses
increases osmotic flow
regulates resting calories expenditure and BMR
provides energy for coupled transport of other molecules
secondary active transport
no direct input of energy is required
typically involves coupled transport
cotransport
transporter moves a molecule or ion in the same direction as another molecule
aka symport
countertransport
transporter moves a molecule or ion in the opposite direction of another molecule
aka antiport
bulk transport
movement of large molecules that can’t be transported by carriers at the same time
types: endocytosis, exocytosis
epithelium
boundary of any intestine
transcellular transport
molecule is transported through the cell
can involve facilitated diffusion, permease, primary/secondary transport, or osmosis
paracellular transport
molecule is transported between cells
ONLY involves simple diffusion
absorption
transport of digestion molecules across intestinal epithelium into blood
reabsorption
transport of molecules out of the urinary filtrate back into the bloodstream
membrane potential
difference in charge between the outside and inside environments
measured as mV
provides energy for cellular functions
depolarization
intracellular environment becomes more positive
hyperpolarization
extracellular environment becomes more positive
what can changes in membrane potential cause?
the opening or closing of channels
