Ch 5: Membrane Dynamics, Part 2Ch 5: Membrane Dynamics, Part 2

Cell membrane structures and functionsCell membrane structures and functions Membranes form fluid body compartmentsMembranes form fluid body compartments Membranes as barriers and gatekeepersMembranes as barriers and gatekeepers How products move across membranesHow products move across membranes

i.e., methods of transporti.e., methods of transport VesicularVesicular TransepithelialTransepithelial OsmosisOsmosis

Distribution of water and solutes in cells & the bodyDistribution of water and solutes in cells & the body Chemical and electrical imbalancesChemical and electrical imbalances

Resting Membrane PotentialResting Membrane Potential Membrane permeability and changesMembrane permeability and changes

Membrane Dynamics, Part 1 Membrane Dynamics, Part 1 ReviewReview

Law of Mass BalanceLaw of Mass Balance Ins = outsIns = outs

DiffusionDiffusion Too slow for many processesToo slow for many processes

Facilitated DiffusionFacilitated Diffusion Carrier proteinsCarrier proteins

Protein-mediated TransportProtein-mediated Transport Very selectiveVery selective

Active Transport uses ATPActive Transport uses ATP NaNa++ - K - K++ ATPase pump ATPase pump

Vesicular TransportVesicular Transport

Movement of Movement of macromoleculesmacromolecules across cell across cell membrane:membrane:

1.1. Phagocytosis (specialized cells only)Phagocytosis (specialized cells only)

2.2. EndocytosisEndocytosis PinocytosisPinocytosis Receptor mediated endocytosisReceptor mediated endocytosis (Caveolae) Potocytosis(Caveolae) Potocytosis

3.3. ExocytosisExocytosis

1. Phagocytosis1. PhagocytosisRequires energy Requires energy

Cell engulfs particle into Cell engulfs particle into vesicle via pseudopod vesicle via pseudopod formationformation

E.g.:E.g.: some WBCs engulf some WBCs engulf bacteriabacteria

Vesicles formed are much Vesicles formed are much larger than those formed by larger than those formed by endocytosisendocytosis

Phagosome fuses with Phagosome fuses with lysosomes lysosomes ? ? (see Fig. 5-23(see Fig. 5-23))

2. Endocytosis2. Endocytosis

Requires energy Requires energy

No pseudopodia - Membrane surface No pseudopodia - Membrane surface indentsindents

Smaller vesiclesSmaller vesicles

Nonselective:Nonselective: Pinocytosis Pinocytosis for fluids & for fluids & dissolved substancesdissolved substances

Selective:Selective: Receptor Mediated EndocytosisReceptor Mediated Endocytosis via clathrin-via clathrin-

coated pitscoated pits - - Example: LDL cholesterol and Example: LDL cholesterol and Familial Hypercholesterolemia Familial Hypercholesterolemia

PotocytosisPotocytosis via caveolae via caveolae

Fig 5-24

Receptor Mediated Endocytosis and Receptor Mediated Endocytosis and Membrane RecyclingMembrane Recycling

Fig 5-28Fig 5-28

3. Exocytosis3. Exocytosis•Intracellular vesicle fuses with membrane Intracellular vesicle fuses with membrane

•Requires energy (ATP) and CaRequires energy (ATP) and Ca2+2+

•Uses:Uses:

•large lipophobic molecule secretion;large lipophobic molecule secretion;

• receptor insertion; receptor insertion;

•waste removalwaste removal

Movement through Epithelia: Movement through Epithelia: Transepithelial TransportTransepithelial Transport

Uses combination of active and passive transportUses combination of active and passive transport

Molecule must Molecule must cross two cross two phospholipid phospholipid

bilayers bilayers

Apical and basolateral cell membranes have different Apical and basolateral cell membranes have different proteinsproteins::NaNa++- glucose transporter on apical membrane- glucose transporter on apical membraneNaNa++/K/K++-ATPase only on basolateral membrane-ATPase only on basolateral membrane

Fig 5-26

Transepithelial Transport of GlucoseTransepithelial Transport of Glucose

1. Na+/Glucose symporter only found on apical side

2. Na+/K+-ATPase only found on basolateral side

3. Facilitated diffusion

TranscytosisTranscytosis

Endocytosis Endocytosis vesicular transport vesicular transport exocytosis exocytosis

Moves large proteins intactMoves large proteins intact

Examples: Examples: Absorption of maternalAbsorption of maternal antibodies from antibodies from

breast milk breast milk

Movement of proteins Movement of proteins across capillary across capillary endotheliumendothelium

Distribution of Solutes in BodyDistribution of Solutes in Body

Depends onDepends onselective permeability of cell membraneselective permeability of cell membranetransport mechanisms availabletransport mechanisms available

Water is in osmotic equilibrium (free Water is in osmotic equilibrium (free movement across membranes)movement across membranes)

Ions and most solutes are in chemical Ions and most solutes are in chemical disequilibrium (e.g., Na-K ATPase Pump)disequilibrium (e.g., Na-K ATPase Pump)

Electrical disequilibrium between ECF and Electrical disequilibrium between ECF and ICFICF

Fig 5-33

Distribution of Solutes in Body Fluid CompartmentsDistribution of Solutes in Body Fluid CompartmentsCompare to Fig 5-33

OsmosisOsmosisMovement of water down its

concentration gradient.Osmotic Osmotic pressurepressure

Opposes movement of water across membrane

WaterWater moves freely in body until osmotic moves freely in body until osmotic equilibrium is reachedequilibrium is reached

Compare to Fig. 5-29

Molarity vs. OsmolarityMolarity vs. Osmolarity

In chemistry:In chemistry:

Mole / LMole / L

Avogadro’s # / LAvogadro’s # / L

In PhysiologyIn Physiology

Important is not # of Important is not # of molecules / L butmolecules / L but

# of particles / L: osmol/L or # of particles / L: osmol/L or OsMOsM

Why?Why?

Osmolarity takes into account dissociation (solubility) of molecules in solutionOsmolality = OsM/Kg of sol’n

Convert Molarity to OsmolarityConvert Molarity to Osmolarity

Osmolarity = # of particles / L of solutionOsmolarity = # of particles / L of solution

1 M glucose = 1 OsM glucose1 M glucose = 1 OsM glucose

1 M NaCl = 2 OsM NaCl1 M NaCl = 2 OsM NaCl

1 M MgCl1 M MgCl22 = 3 OsM MgCl = 3 OsM MgCl22

Osmolarity of human body ~ 300 mOsMOsmolarity of human body ~ 300 mOsM

Compare isosmotic, hyperosmotic, hyposmotic (p Compare isosmotic, hyperosmotic, hyposmotic (p 156)156)

TonicityTonicity

Physiological term describing how cell Physiological term describing how cell volume changes if cell placed in the volume changes if cell placed in the solutionsolution

Always comparative. Has no units.Always comparative. Has no units. Isotonic sol’n = No change in cellIsotonic sol’n = No change in cell Hypertonic sol’n = cell shrinksHypertonic sol’n = cell shrinks

Hypotonic = cell expandsHypotonic = cell expands

Depends not just on osmolarity but on Depends not just on osmolarity but on nature of solutes and permeability of nature of solutes and permeability of membranemembrane

Penetrating vs. Nonpenetrating Penetrating vs. Nonpenetrating SolutesSolutes

Penetrating solute: can enter cell Penetrating solute: can enter cell (glucose, urea)(glucose, urea)

Nonpenetrating solutes: cannot enter Nonpenetrating solutes: cannot enter cell (sucrose, NaCl*)cell (sucrose, NaCl*)

Determine relative conc. of Determine relative conc. of nonpenetrating solutes in solution and nonpenetrating solutes in solution and in cell to determine tonicity.in cell to determine tonicity.

Water will move to dilute nonpenetrating solutesWater will move to dilute nonpenetrating solutes Penetrating solutes will distribute to equilibriumPenetrating solutes will distribute to equilibrium

Fig 5-30

IV Fluid TherapyIV Fluid Therapy

2 different purposes:2 different purposes: Get fluid into dehydrated cells orGet fluid into dehydrated cells or Keep fluid in extra-cellular compartmentKeep fluid in extra-cellular compartment

Electrical Disequilibrium and Resting Membrane Potential (pp.156-163) will be covered at the beginning of Ch 8

Which of the following is a way for solutes in a Which of the following is a way for solutes in a aqueous solution to move from an area of high aqueous solution to move from an area of high solute concentration to an area of low solute solute concentration to an area of low solute concentration?concentration?

A.A. Facilitated diffusionFacilitated diffusion

B.B. OsmosisOsmosis

C.C. Active transportActive transport

D.D. A and BA and B

E.E. None of theseNone of these

Which of the following defines the Which of the following defines the term specificity?term specificity?

A. movement of molecules by the use of vesicles

B. the energy required to move molecules

C. a group of carrier proteins operating at their maximum rate

D. carrier transport of a group of closely related molecules

E. none of these

Water will always move from ___________ Water will always move from ___________ situations to _______ situations.situations to _______ situations.

A.A. Hyperosmotic, hyposmoticHyperosmotic, hyposmotic

B.B. Hyposmotic, hyperosmoticHyposmotic, hyperosmotic

C.C. Hyposmotic, isosmoticHyposmotic, isosmotic

D.D. Hyperosmotic, isosmoticHyperosmotic, isosmotic

Which of the following pairs of molecular Which of the following pairs of molecular characteristics favors diffusion through the characteristics favors diffusion through the cell membrane?cell membrane?

A.A. Large, polarLarge, polar

B.B. Large, non-polarLarge, non-polar

C.C. Small, polarSmall, polar

D.D. Small, non-polarSmall, non-polar

Which of the following is a way for solutes in a Which of the following is a way for solutes in a aqueous solution to move from an area of high aqueous solution to move from an area of high solute concentration to an area of low solute solute concentration to an area of low solute concentration?concentration?

A.A. Facilitated diffusionFacilitated diffusion

B.B. OsmosisOsmosis

C.C. Active transportActive transport

D.D. A and BA and B

E.E. None of theseNone of these