sign in sign up
<<
Home , Facilitated diffusion, Passive transport, Potocytosis

 Epithelial Ch 1: Membrane Dynamics – vs. 2 Meanings!  membranes and Membranes around organelles structures and functions

 Membranes form fluid body compartments

 Membranes as barriers and gatekeepers

 How products move across membranes

 i.e., methods of transport

 Distribution of water and solutes in cells & the body

 Chemical and electrical imbalances

 Membrane permeability and changes

Thickness ~ 8nm Membrane Structure: to Cell Membrane Structure: Fluid Mosaic Model Ratio varies from cell type to cell type

PLs Ratio for cells with high metabolic activity? Cholesterol : peripheral (associated) or integral

Membrane Other Behaviors in

Proteins H2O:

Integral  Phospholipid bilayer (Membrane- Associated spanning or (peripheral or  Micelle intrinsic ) extrinsic)  Role in digestion and absorption of fats in GI  Can span membrane  Loosely bound to tract several times membrane

  Either move around or Liposome are kept in place by  Enzymes and  Larger, bilayer, hollow cytoskeleton proteins structural proteins center with aqueous core Clinical relevance? Allows for cell polarity

11 Movement across Membrane = (Def?) – 3 types:

1. simple diffusion Membrane permeability varies for 2. 3. (= ) different & cell types Two movement categories: depends on?? Always protein-mediated – 3 types:  Passive and  co -transport  vesicular transport  Active  receptor mediated transport

Cytoskeleton Proteins Membrane Spanning Protein anchor membrane proteins

Fig 5-5

Diffusion Process (Passive) Distance – Time Relationship •Uses of concentration Time for diffusion to progress to given gradient •Net movement until state of distance ~ to distance squared equilibrium reached (no more conc. gradient) diffusion over 100 m takes 5 sec. •Direct correlation to temperature (why?) (why?) Fig 5-5 •Indirect correlation to diffusion over 200 m takes ?? size •Slower with increasing distance diffusion over 400 m takes ?? •Lipophilic molecules can difuse through the phospholipid bilayer through the phospholipid bilayer diffusion over 800 m takes ??

Diffusion effective only over short distances!

22 Membrane Proteins

Fick’s law of Diffusion (p 135)

surface area x conc. gradient rate of = diffusion membrane resistance x membrane thickness Fig 5-7

depends on size and lipid-solubility of molecule and composition of

Transporters Protein-Mediated Transport Cell Membrane Regulates Exchange with Environment  More selective Many molecules use transporters to  Active or Passive cross cell membrane. Why? Examples ?  Membrane Proteins  Structural Two categories of transporter proteins  Enzymes 1. Channel proteins (rapid but not as  Receptors selective – for small molecules only, e.g.,  Transporters (allows Specificity, water and ions) Competition, Saturation p 145) 2. Carrier proteins (slower but very  Channel selective – also works for large  Gated molecules)

Open Channels vs. Gated 1. Channel Proteins 1. Channel Proteins Channels Channels Gates closed most of the time  For small molecules such as ?? = pores Chemically gated channels (controlled by messenger molecule Have gates, but or ligand)  Aquaporin; plus > 100 gates are open ion channels most of the time. Voltage gated channels (controlled by electrical state of cell) Also referred to as  Selectivity based on “leak channels”. Mechanically gated size & charge of channels (controlled by physical state of cell: temp.; stretching of cell molecule membrane etc.)

 All have gate region

 Open

 Gated

33 Cotransport 2. Carrier Proteins Symport  Never form direct connection  Molecules are carried between ECF and ICF – 2 in same direction gates!  Examples: +  Bind molecules and change and Na conformation Antiport

 Used for small organic  Molecules are carried molecules (such as?) in opposite direction + +  Examples: Na /K  Ions may use channels or pump carriers

 Rel. slow (1,000 to 1 Mio / sec)

Facilitated Diffusion (as a Active Transport form of carrier mediated transport)

Some characteristics same as simple  Movement from low diffusion conc. to high conc.  ATP needed

but also:  Creates state of dis equilibrium  specificity o  competition  1 (direct) active transport  saturation  ATPases or “pumps ” (uniport and antiport)– examples? Figs 5-18/20 o  2 (indirect) active transport  Symport and antiport

1o (Direct) Active Transport Mechanism of the Na +/K +- ATPase  ATP energy directly fuels transport

+ + start  Most important example: Na /K pump = sodium-potassium ATPase (uses up to 30% of cell’s ATP)

Fig 5-16

 Establishes Na+ ECF: high [Na +], low [K +] conc. gradient ⇒⇒⇒ ICF: high [K +], low [Na +] Epot. can be harnessed for other cell functions Fig 5-17

44 2o (Indirect) Active Transport Body Fluid Compartments

 Indirect ATP use: uses Epot. stored in concentration gradient IC fluid EC fluid (of Na + and K +)

 Coupling of Ekin of one molecule with movement Exchange of another molecule much more selective; Interstitial fluid plasma +  Example: Na / Glucose Why ? Relatively free exchange

 other examples

 2 mechanisms for Glucose transport Fig 5-13

Body Fluid Compartments: Competition and Saturation Critical Thinking Question Fig 20 Fig 5-18 Glucose and use same transport protein ECF ICF What properties should a molecule have to be used as marker for one of the fluid compartments?

Do total H 2O; total EC and plasma. Then, how do you figure out ICF and interstitial fluid? Saturation of carrier mediated transport:

Table 5-4 Vesicular Transport

Movement of macromolecules across cell membrane: 1. (specialized cells only)

2.   Receptor mediated endocytosis  ()

3.

55 2. Endocytosis 1. Phagocytosis  Requires energy  Requires energy  No pseudopodia - Membrane surface indents

 Cell engulfs particle into vesicle via  Smaller vesicles pseudopodia formation  Nonselective: Pinocytosis for fluids & dissolved  E.g.: some WBCs engulf substances

 Vesicles formed are much larger than those  Selective:  Receptor Mediated Endocytosis via -coated formed by endocytosis pits - Example: LDL cholesterol and Familial Hypercholesterolemia  Phagosome fuses with lysosomes ⇒ ? (see ⇒⇒  Podocytosis via caveolae Fig 5-24 Fig. 5-23)

Receptor Mediated Endocytosis and Membrane Recycling 3. Exocytosis Intracellular vesicle fuses with membrane →→→ Requires energy (ATP) and Ca 2+ Examples: large lipophobic molecule secretion; receptor insertion; waste removal

Fig 5-28

Movement through Epithelia: Transepithelial Transport of Glucose Transepithelial transport 1. Na +/Glucose symporter only found Uses combination of active and passive transport on apical side apical 2. Na +/K +-ATPase only Molecule must found on basolateral cross two side phospholipid bilayers 3. Facilitated diffusion basolateral

Apical and basolateral cell membranes have different proteins : Na +- on apical membrane Na +/K +-ATPase only on basolateral membrane Fig 5-26 Concept check: Apply Ouabain to either side of cell, what happens?

66 Distribution of Solutes in Body  Endocytosis →→→ vesicular transport →→→ exocytosis Depends on  selective permeability of cell  Moves large proteins intact membrane  transport mechanisms available  Examples: Water is in osmotic equilibrium (free  Absorption of maternal movement across membranes) antibodies from breast milk Ions and most solutes are in chemical disequilibrium (e.g., Na-K ATPase  Movement of proteins Pump) across endothelium Electrical disequilibrium between ECF and ICF Fig 5-33

Distribution of Solutes in Body Fluid Compartments Compare to Fig. 5-29 Compare to Fig 5-33 Osmosis Movement of water down its concentration gradient. Opposes movement Osmotic of water across membrane

Water moves freely in body until osmotic equilibrium is reached

Convert Molarity to Molarity vs. Osmolarity Osmolarity

In chemistry: In Physiology Osmolarity = # of particles / L of solution

 Mole / L Important is not # of  1 M glucose = 1 OsM glucose molecules / L but  Avogadro’s # / L  1 M NaCl = 2 OsM NaCl # of particles / L: osmol/L or OsM  1 M MgCl 2 = 3 OsM MgCl 2 Why?  Osmolarity of human body ~ 300 mOsM Osmolarity takes into account

dissociation (solubility) of molecules  Compare isosmotic, hyperosmotic, hyposmotic (p in solution 156) Osmolality = OsM/Kg of sol’n

77 Tonicity Penetrating vs. Nonpenetrating Solutes

 Physiological term describing how  Penetrating solute: can enter cell cell volume changes if cell placed in (glucose, urea) the solution  Nonpenetrating solutes: cannot enter  Always comparative. Has no units. cell (sucrose, NaCl*)

 Isotonic sol’n = No change in cell  Determine relative conc. of  Hypertonic sol’n = cell shrinks nonpenetrating solutes in solution  Hypotonic = cell expands and in cell to determine tonicity.  Water will move to dilute nonpenetrating solutes  Depends not just on osmolarity but  Penetrating solutes will distribute to equilibrium on nature of solutes and permeability of membrane Fig 5-30

Osmolarity and Tonicity IV Fluid Therapy Comparison 2 different purposes:

 Get fluid into dehydrated cells or

 Keep fluid in extra-cellular compartment

A is isosmotic to B A is hypotonic to B

Compare to Fig 5-35

Ch 5: Membrane Dynamics, Part 2 Electrical Disequilibrium and

Resting Cell membrane structures and functions (pp.156-163) will be covered at the  Membranes form fluid body compartments beginning of Ch 8  Membranes as barriers and gatekeepers  How products move across membranes

 i.e., methods of transport

 Vesicular

 Transepithelial

 Osmosis

 Distribution of water and solutes in cells & the body

 Chemical and electrical imbalances

 Resting Membrane Potential

 Membrane permeability and changes

88 Membrane Dynamics, Part 1 Review Vesicular Transport

 Law of Mass Balance Movement of macromolecules across

 Ins = outs cell membrane: 1. Phagocytosis (specialized cells  Diffusion only)  Too slow for many processes  Facilitated Diffusion 2. Endocytosis  Pinocytosis  Carrier proteins  Receptor mediated endocytosis  Protein-mediated  (Caveolae) Potocytosis Transport  Very selective 3. Exocytosis  Active Transport uses ATP + +  Na -K ATPase pump

2. Endocytosis 1. Phagocytosis

 Requires energy  Requires energy  Cell engulfs particle into vesicle via pseudopod  No pseudopodia - Membrane surface formation indents

 E.g.: some WBCs engulf  Smaller vesicles bacteria

 Vesicles formed are much  Nonselective: Pinocytosis for fluids & larger than those formed by dissolved substances endocytosis  Selective:  Phagosome fuses with  Receptor Mediated Endocytosis via clathrin- Fig 5-24 lysosomes ⇒⇒⇒ ? (see Fig. 5-23 ) coated pits - Example: LDL cholesterol and Familial Hypercholesterolemia

 Potocytosis via caveolae

Receptor Mediated Endocytosis and 3. Exocytosis Membrane Recycling •Intracellular vesicle fuses with membrane →→→ •Requires energy (ATP) and Ca 2+ •Uses: •large lipophobic molecule secretion; • receptor insertion; •waste removal

Fig 5-28

99 Movement through Epithelia: Transepithelial Transport of Glucose Transepithelial Transport 1. Na +/Glucose symporter only Uses combination of active and passive transport found on apical side

2. Na +/K +-ATPase Molecule must only found on cross two basolateral side phospholipid bilayers 3. Facilitated diffusion

Apical and basolateral cell membranes have different proteins : Na +- glucose transporter on apical membrane Na +/K +-ATPase only on basolateral membrane Fig 5-26

Transcytosis Distribution of Solutes in Body  Endocytosis →→→ vesicular transport →→→ exocytosis Depends on  Moves large proteins intact  selective permeability of cell membrane  Examples:  transport mechanisms available  Absorption of maternal antibodies from Water is in osmotic equilibrium (free breast milk movement across membranes) Ions and most solutes are in chemical  Movement of proteins disequilibrium (e.g., Na-K ATPase across capillary Pump) endothelium Electrical disequilibrium between ECF Fig 5-33 and ICF

Distribution of Solutes in Body Fluid Compartments Compare to Fig. 5-29 Compare to Fig 5-33 Osmosis Movement of water down its concentration gradient. Opposes Osmotic movement of water pressure across membrane

Water moves freely in body until osmotic equilibrium is reached

1010 Convert Molarity to Molarity vs. Osmolarity Osmolarity

In chemistry: In Physiology Osmolarity = # of particles / L of solution  Mole / L Important is not # of

 Avogadro’s # / L molecules / L but  1 M glucose = 1 OsM glucose

# of particles / L: osmol/L  1 M NaCl = 2 OsM NaCl or OsM  1 M MgCl 2 = 3 OsM MgCl 2 Why? Osmolarity takes into account  Osmolarity of human body ~ 300 mOsM dissociation (solubility) of molecules in solution  Compare isosmotic, hyperosmotic, Osmolality = OsM/Kg of sol’n hyposmotic (p 156)

Tonicity Penetrating vs. Nonpenetrating Solutes

 Penetrating solute: can enter cell  Physiological term describing (glucose, urea) how cell volume changes if cell  Nonpenetrating solutes: cannot enter placed in the solution cell (sucrose, NaCl*)  Always comparative. Has no  Determine relative conc. of units. nonpenetrating solutes in solution  Isotonic sol’n = No change in cell and in cell to determine tonicity.  Hypertonic sol’n = cell shrinks  Water will move to dilute nonpenetrating solutes  Penetrating solutes will distribute to equilibrium  Hypotonic = cell expands

 Depends not just on osmolarity but on nature of solutes and Fig 5-30 permeability of membrane

Osmolarity and Tonicity IV Fluid Therapy Comparison

2 different purposes:

 Get fluid into dehydrated cells or

 Keep fluid in extra-cellular compartment

A is isosmotic to B A is hypotonic to B

Compare to Fig 5-35

1111 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 defines the aqueous solution to move from an area of high term specificity? solute concentration to an area of low solute concentration? A. movement of molecules by the use of vesicles

B. the energy required to move molecules

A. Facilitated diffusion C. a group of carrier proteins operating at their maximum rate B. Osmosis D. carrier transport of a group of closely C. Active transport related molecules D. A and B E. none of these E. None of these

Water will always move from ______situations to ______Which of the following pairs of molecular situations. characteristics favors diffusion through the cell membrane?

A. Hyperosmotic, hyposmotic A. Large, polar

B. Hyposmotic, hyperosmotic B. Large, non-polar

C. Hyposmotic, isosmotic C. Small, polar

D. Hyperosmotic, isosmotic D. Small, non-polar

1212 Which of the following is a way for solutes in a aqueous solution to move from an area of high solute concentration to an area of low solute concentration?

A. Facilitated diffusion

B. Osmosis

C. Active transport

D. A and B

E. None of these

1313