Plasma membrane is a phospholipid bilayer Protein “icebergs” float in a “sea” of phospholipids

The Cell Membrane

PhospholipidsPhospholipids

Phosphate group Phosphate group forms a forms a hydrophilichydrophilic headhead

Fatty acid tails are Fatty acid tails are hydrophobichydrophobic

Membrane proteins perform a variety of cell Membrane proteins perform a variety of cell functionsfunctions::

Cell Signaling

The Plasma Membrane is The Plasma Membrane is Selectively PermeableSelectively Permeable

What does this mean?What does this mean?

Permeable to:Permeable to:

small molecules, nonpolar small molecules, nonpolar moleculesmolecules

Less Permeable to:Less Permeable to:

charged ions, large molecules, charged ions, large molecules, or hydrophilic moleculesor hydrophilic molecules

What molecules can go What molecules can go directlydirectly through?through?

Carbohydrates?Carbohydrates? No, large & hydrophilicNo, large & hydrophilic

Proteins?Proteins? No, large; many hydrophilicNo, large; many hydrophilic

Lipids?Lipids? Yes; hydrophobicYes; hydrophobicNucleic acids?Nucleic acids? No, hydrophilicNo, hydrophilic

Water?Water? No; hydrophilicNo; hydrophilic

TRANSPORTTRANSPORT

WHY?WHY?

To maintain To maintain HomeostasisHomeostasis

TRANSPORTTRANSPORT

HOW?HOW?

A.A. By Passive ProcessesBy Passive Processes

B.B. By Active ProcessesBy Active Processes

Passive Processes: Passive Processes: DiffusionDiffusion

The movement of moleculesThe movement of molecules

from a region of their from a region of their high high

concentration to a region concentration to a region

of their of their lowlow concentration. concentration.

A drop of food coloring diffuses through gelatin in a petri dish

Figure 8.10 The diffusion of solutes across membranesFigure 8.10 The diffusion of solutes across membranes

Additional TerminologyAdditional Terminology

EquilibriumEquilibrium

Concentration GradientConcentration GradientDifference in concentration Difference in concentration

between 2 regionsbetween 2 regions

All molecules diffuse All molecules diffuse downdown their concentration their concentration gradientgradient

OSMOSISOSMOSIS Special case of Special case of

DiffusionDiffusion1. Movement of Water1. Movement of Water

2. 2. from an area of high from an area of high concentration to an area of concentration to an area of low concentrationlow concentration

3. 3. across a selectively across a selectively permeable membrane.permeable membrane.

Osmosis AnimationOsmosis Animation

Gatorade vs. Gatorade vs. Powerade Powerade

Osmosis LabOsmosis Lab

Solutes and Their EffectsSolutes and Their EffectsHypotonicHypotonicA solution is hypotonic to a second solution if it has A solution is hypotonic to a second solution if it has

less solute dissolved in it than the second solutionless solute dissolved in it than the second solution

HypertonicHypertonicA solution is hypertonic to a second solution if it has A solution is hypertonic to a second solution if it has

more solute dissolved in it than the second solutionmore solute dissolved in it than the second solution

IsotonicIsotonicA solution that has equal amounts of solute as the A solution that has equal amounts of solute as the

second solutionsecond solution

Solutes and Their EffectsSolutes and Their Effects

Water moves from a ________Water moves from a ________

solution to a _________ onesolution to a _________ one

•Water flow equal in both directions

(Equilibrium)

•Net water flow into the cell which can burst

(Hemolysis)

Net water flow out of cell which shrinks(Crenation)

Water Balance in Animal Cells

The contractile vacuole of The contractile vacuole of ParameciumParamecium: an evolutionary adaptation for : an evolutionary adaptation for osmoregulationosmoregulation

PlasmolysisPlasmolysis

Shrinking of cytoplasm due to Shrinking of cytoplasm due to water losswater loss

Plasmolyzed cells become Plasmolyzed cells become FLACCID.FLACCID.

What is the opposite? Swollen What is the opposite? Swollen cells are cells are TURGIDTURGID..

A watered tomato plant regains its turgorA watered tomato plant regains its turgor

Water Balance in Plant CellsRed Onion CellsRed Onion Cells

TurgidTurgid Flaccid Flaccid

Concept GeneralizationsDiffusion:Diffusion: equilibrium, molecules, high equilibrium, molecules, high

concentration, low concentration, concentration, low concentration, passive process, concentration gradientpassive process, concentration gradient

Osmosis:Osmosis: water, passive, high water, passive, high concentration, low concentration, concentration, low concentration, selectively permeable membrane, selectively permeable membrane, hypotonic, hypertonic, isotonic, hypotonic, hypertonic, isotonic, plasmolyzed, flaccid, shrivelplasmolyzed, flaccid, shrivel

Passive transport – diffusion across a selectively permeable membrane

No energy is required. The random movement of molecules move them across the membrane

Facilitated diffusion – specific transport proteins provide a pathway for certain molecules to pass

Is this active or passive transport?

Active transport : ATP (an energy rich molecule) is used to move materials across the membrane against their concentration gradient.

EXAMPLES: 1. Metabolic Pumps: A specific transport protein

pumps solute across a membrane

Example Na+(Sodium) K+(Potassium) pump operates in all cells to maintain charge on the membrane

Figure 8.16 Review: passive and active transport comparedFigure 8.16 Review: passive and active transport compared

Endocytosis – Vesicles form to engulf materials and bring them inside the cell

Exocytosis – spills contents outside the cell

BOTH transport large molecules packaged in vesicles (small membrane sacs)

PhagocytosisPhagocytosisPinocytosisPinocytosis