The Plasma MembraneThe Plasma Membrane

FunctionFunction

• Separate the cell from its Separate the cell from its environmentenvironment

• Control the traffic that enters & Control the traffic that enters & exits the cellexits the cell

The main ingredient in the The main ingredient in the plasma membraneplasma membrane

• The phospholipid The phospholipid moleculemolecule

How is the membrane How is the membrane “fluid”?“fluid”?

• Membrane is held Membrane is held together by weak together by weak hydrophobic hydrophobic interactionsinteractions

• The lipids drift The lipids drift about laterally about laterally causing a causing a “liquidy” action“liquidy” action

Why is the membrane a Why is the membrane a “mosaic”?“mosaic”?

• It is made of many different It is made of many different molecules:molecules:

• PhospholipidsPhospholipids• ProteinsProteins• CarbohydratesCarbohydrates• Cholesterol (animal cells only)Cholesterol (animal cells only)

Categories of proteins that Categories of proteins that exist in membranesexist in membranes

• Integral proteins—penetrate the Integral proteins—penetrate the hydrophobic core of lipidshydrophobic core of lipids– Transmembrane proteins—completely span Transmembrane proteins—completely span

the membranethe membrane

• Peripheral proteins—are not embedded Peripheral proteins—are not embedded in the lipid layerin the lipid layer– Interior ones attach to the cytoskeletonInterior ones attach to the cytoskeleton– Exterior ones attach to the extracellular Exterior ones attach to the extracellular

matrixmatrix

Membrane carbohydrate Membrane carbohydrate functionfunction

• Cell-Cell RecognitionCell-Cell Recognition• Recognition carbohydrates Recognition carbohydrates

different from species to species & different from species to species & organism to organismorganism to organism

• Important in embryology & immune Important in embryology & immune responseresponse

The function of cholesterolThe function of cholesterol

• Give extra rigidity to the animal Give extra rigidity to the animal cell plasma membranecell plasma membrane

Functions of membrane Functions of membrane proteinsproteins

• Transport molecules through the Transport molecules through the membranemembrane

• Act as an enzymeAct as an enzyme• Send a signal to the inside of the cell to Send a signal to the inside of the cell to

start a reactionstart a reaction• Hook together adjacent cellsHook together adjacent cells• Work with carbs for cell-cell recognitionWork with carbs for cell-cell recognition• Attach to cytoskeleton or extracellular Attach to cytoskeleton or extracellular

matrixmatrix

Control of Cellular TrafficControl of Cellular Traffic

What can pass through What can pass through the membrane?the membrane?

• Small hydrophobic molecules such Small hydrophobic molecules such as Oas O22 and CO and CO22

What cannot pass directly What cannot pass directly through the membrane?through the membrane?

• Large MoleculesLarge Molecules• Hydrophilic molecules such as Hydrophilic molecules such as

glucose, water, and ions (Naglucose, water, and ions (Na++, Cl, Cl--, , etc.)etc.)

How do these molecules How do these molecules get it?get it?

• They have to pass through They have to pass through channels in the membranechannels in the membrane

• These channels are transport These channels are transport proteins that span the entire proteins that span the entire bilayerbilayer

• They are very specific to the They are very specific to the molecule they will transportmolecule they will transport

Passive TransportPassive Transport

• Movement of molecules DOWN the Movement of molecules DOWN the concentration gradientconcentration gradient

• Does not require any work from the Does not require any work from the cell (no expenditure of energy)cell (no expenditure of energy)

• It is spontaneousIt is spontaneous

DiffusionDiffusion

• A type of passive transportA type of passive transport• The random “spreading” of The random “spreading” of

moleculesmolecules• Examples perfume aroma Examples perfume aroma

spreading, food coloring spreading, spreading, food coloring spreading, etc.etc.

Diffusion across cell Diffusion across cell membranemembrane

• Oxygen passing into a cellOxygen passing into a cell

• COCO22 passing out of a cell passing out of a cell

OsmosisOsmosis

• The DIFFUSION of water across a The DIFFUSION of water across a selectively permeable membraneselectively permeable membrane

Terms comparing solution Terms comparing solution concentrationsconcentrations

• Isotonic—the two solutions have Isotonic—the two solutions have equal concentrations of soluteequal concentrations of solute

• Hypertonic—the solution with the Hypertonic—the solution with the higher concentration of solutehigher concentration of solute

• Hypotonic—the solution with the Hypotonic—the solution with the lower concentration of solutelower concentration of solute

KEY IDEAKEY IDEA

•Water ALWAYS Water ALWAYS moves toward the moves toward the HYPERTONIC HYPERTONIC solution!!!!!!solution!!!!!!

Animal vs. Plant CellsAnimal vs. Plant Cells

• Plant cells can take a higher water Plant cells can take a higher water pressure because of their rigid cell wall.pressure because of their rigid cell wall.

• When plant cells’ vacuole is full and When plant cells’ vacuole is full and pressing against the outside of the cell it pressing against the outside of the cell it is TURGID.is TURGID.

• When the vacuole does not press When the vacuole does not press against the outside of the cell it is against the outside of the cell it is FLACCID.FLACCID.

Contractile Vacuoles are Contractile Vacuoles are adaptations to deal with adaptations to deal with increased water pressureincreased water pressure