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66 Cards in this Set

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Plasma Membranes:
-Barrier between ECF and ICF
-Selective permeability
What is selective permeability in the plasma membrane?
Non-polar and some small polar cross easily (O2, CO2, fatty acids, water, ethanol, urea, steroids)

Large polar molecules and ions can't cross (glucose, proteins, ions)
No energy required,
Simple diffusion or mediated transport,
DOWN concentration gradient
Passive transport
Requires energy,
Requires pumps,
UP concentration gradient
Active transport
What are the 5 modes of passive transport?
1. Simple diffusion
2. Facilitated Diffusion
3. Osmosis
4. Dialysis
5. Filtration
Simple diffusion
Movement of molecules through the phospholipid bilayer from an area of high concentration to an area of lower concentration (i.e. DOWN the concentration gradient).
Simple diffusion
-powered by random movement of molecules (Brownian motion)
-diffusions of different substances do not interfere with one another (no competition)
-in general, substances can cross membranes by diffusion if they can dissolve in the hydrophobic (OILY) interior of the membrane
-diffusions can also occur through tight junctions between cells
-does NOT saturate as the concentration or gradient changes
In simple diffusion, do molecules/ions stop moving after an equilibrium is reached?
NO! There just is no NET movement (net flux).

Examples: H2O, O2, CO2, fatty acids, ethanol, urea, steroids, lipid-soluble vitamins (D,K,E)
What are the factors affecting rate of simple diffusion?
1. Concentration difference- larger difference or higher concentration, faster
2. Size of molecule- large diffuse slower
3. Temperature- faster at higher temps
4. Surface area of membrane- greater area means faster diffusion (e.g. in emphysema, air sacs of lungs are destroyed so there is less surface area)
5. Thickness of membrane- thinner faster
6. Ability of molecule to dissolve in membrane - lipophilic molecules faster
LOOK UP diagrams:
Model of simple diffusion,
Magnitude of driving force,
Concentration gradient,
Membrane permeability
Facilitated Diffusion
Carrier-mediated passive transport

Diffusion of particles through a membrane by means of carrier proteins

Fig. 4-21
Facilitated Diffusion
-permits flux of substances that cannot diffuse directly through the membrane
-movement is still passive and direction is still from high conc. to low conc.
-saturates when substance reaches high concentrations due to lack of available protein carriers
-related substances CAN compete for the same carrier protein
-specificity between substance and its carrier protein
LOOK UP diagrams:
Effect of concentration gradient on rate of facilitated diffusion (Fig 4-20, Fig. 4-23)
Facilitated Diffusion Model
-Affinity of carrier for molecule is same on both sides of membrane
-Molecule binds most to side of greater concentration
(diagram on page 4 of lecture slides)
-Transport rate of individual carriers (chemical or electrochemical gradient; affinity for transported substance)
-number of carriers in the membrane
Factors affecting rate of facilitated diffusion
Facilitated diffusion through ION CHANNELS
-open to both intra- and extracellular fluid
a. open (leak) channels- open most of time, free diffusion in both directions
b. gated channels- many are closed most of the time; sensitive to voltage, chemicals (ligands), or mechanical force

Problems with channels can lead to disease: e.g. cystic fibrosis results from mutation in Cl- channel in lungs.
Factors affecting the rate of transport through ion channels
1. Transport rate of individual channels
-electrochemical gradient
-binding interactions between ion and channel
Factors affecting the rate of transport through ion channels:
2. Number of channels in the membrane
-open channels
-closed channels
Look up
Fig. 6-32
Diffusion of water across a membrane in the presence of at least one impermeable solute

(Or, diffusion of water across a membrane that limits the diffusion of at least one solute)
-Most membranes freely permeable to water
-Water diffuses from high to love water concentration (high water conc. = low solute conc., low water conc. = high solute conc.)
-water diffuses from low to high solute concentration
concentration of solute particles
Osmolarity of ICF and ECF=
280-296 mOsm (=300 mOsm)
150 mM NaCl (~0.9%) = 300 mOsm

150 mM glucose = 150 mOsm

150 mM MgCl2 = 450 mOsm
Examples of osmolarity
solutions with same osmolarity
solution with greater osmolarity
solution with lesser osmolarity
the water pressure that develops in a solution as a result of osmosis into that solution

the pressure that must be applied to a solution to just prevent the osmosis
osmotic pressure
Osmotic pressure
greater solute concentration = greater potential osmotic pressure
Water flows _____ osmotic pressure gradient.
UP. (from low to high osmotic pressure)

*Also remember at equilibrium, there is no net movement of water
What is the end result of osmosis?
Gain or loss of volume
Direction of osmosis can be predicted if:
Total solute concentrations are known on both sides
What is tonicity?
describes behavior of cells when placed in a solution

specifically, related to changes in cell volume

same concept as osmolarity, more related to cells
Tonicity of solutions:
depends on relative concentrations of non-permeating solutes inside cell and in the solution
no change in cell size (equal concentrations non-permeating solutes inside and out)
cell swells (lesser concentration non-permeating solutes outside cell)
cell shrinks (greater concentration non-permeating solutes outside cell)
Donnan equilibrium
if diffusible solutes are separated by a membrane that is freely permeable to water and electrolytes but totally impermeable to one ionic species, the diffusible solutes become unequally distributed between the 2 compartments.
What is reverse osmosis?
when pure water is produced by forcing water in impure, waste, or saline fluids through a semipermeable membrane against the water concentration gradient (HYPERFILTRATION)
Diffusion of small particles, but not larger ones, through a semipermeable membrane; resulting in separation of large and small solutes
Peritoneal dialysis
1. Dialysis fluid is introduced to the abdominal cavity via the catheter
2. Toxins and water are absorbed by the fluid through the peritoneal membrane
3. The "dirty" fluid is then drained out and replaced with new clean fluid for further dialysis
movement of solutes through a membrane down the hydrostatic pressure gradient

Active transport properties
-move molecule AGAINST electrochemical gradient
-requires energy
-affinity of carrier greater when facing one side of membrane
Active transport
Primary active transport
Secondary active transport

Other active transport processes:
-Endocytosis (phagocytosis, pinocytosis)
Primary active transport
-movement of solute particles from an area of low conc to high conc (UP conc gradient) through PM by means of a carrier molecule that uses ATP DIRECTLY

saturates when substance reaches high concentration due to lack of available protein carrier
Primary active transport
Carrier protein = ATPase = pump (ATP+Carrier --> ADP+Carrier-P)

Phosphorylation = covalent modulation (changes affinity by changing conformation)
Examples of Primary active transport
*Na+/K+ pump (NA+/K+ ATPase)*
Ca2+ pump
H+/K+ pump
Primary active transport
(sodium-potassium pump)
-present in nearly all cells of body
-transports 3 sodium out of cell and 2 potassium into cell per ATP
-electrogenic (net +1 charge out of cell)
-creates conc gradients for sodium and potassium across cell membranes
All animal cells:
more K+ inside
more Na+ outside
Primary active transport
Sodium-Potassium pump
1. Transporter binds 3 Na+ from cytosol.
2. Phosphorylation by ATP favors conformationational change.
3. Na+ is released, K+ binds.
4. Dephosphorylation favors original conformation.
5. K+ is released to cytosol. Cycle can repeat.
Primary active transport
Ca2+ Pump
Located in PM and ER of some organelles

Purpose: to maintain low cytosolic [Ca].....make it very sensitive to any change (Ca is an important signaling ion)
Secondary active transport
DOES NOT use ATP DIRECTLY but takes advantage of a previously existing concentration gradient, which was created/maintained by primary active transport
Secondary active transport... How it works
A transport protein couples the flow of one substance to that of another across the PM.
One substance (Na+) moves passively DOWN its electrochemical gradient, in the process releasing energy that is then used to drive the movement of the other substance UP its electrochemical gradient
Secondary active transport
-one ion moves DOWN conc gradient causing another ion/molecule to move against its conc gradient
-most common ion- sodium
-ATP needed to maintain gradient for ion
-ion acts as allosteric modulator- changes affinity of carrier for molecule to be transported

(2 entities moving through a single protein)
What are the 2 types of Secondary active transport?
co-transport (symport)

counter-transport (exchange, antiport)
Secondary active transport
move 2 or more molecules in the SAME direction
Cotransport with Na+ renders substrate transport against its conc gradient energetically ______.
Secondary active transport
move 2 or more molecules in OPPOSITE directions
Endocytosis: Phagocytosis
taking in solid particles

movement of a cell or large particle into a cell by trapping it in a section of PM that pinches off to form an intracellular vesicle
Endocytosis: Pinocytosis
taking in liquids

movement of fluid and dissolved substances into a cell by trapping them in a section of PM that pinches off to form an intracellular vesicle
Movement of proteins or other cell products enclosed in a secretory vesicle out of the cell by fusing the secretory vesicle with the PM (movement from inside --> out)
What are the functions of exocytosis?
-add components to PM
-recycle receptors and membrane removed during endocytosis
-secrete specific substance from cell (e.g. protein hormones)
involves both endocytosis and exocytosis.

large molecule is taken into an epithelial cell of the intestine by endocytosis, then the intracellular endocytotic vesicle travels to the opposite side of the cell and fuses with the PM to release its content by exocytosis
Epithelial transport = transport in the intestine
-epithelium- barrier between internal and external environments
-absorption- transport from external environment to internal environment
-secretion- transport from internal environment to external environment
-transport requires movement across 2 membranes
facilitated diffusion and cotransport....
include glucose
in epithelial water transport, active transport of solute is followed by...
transport of water (osmosis)