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1 The Plasma Membrane The Plasma Membrane - Gateway to the Cell Gateway to the Cell

1 The Plasma Membrane The Plasma Membrane - Gateway to the Cell

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Page 1: 1 The Plasma Membrane The Plasma Membrane - Gateway to the Cell

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The Plasma The Plasma MembraneMembrane -

Gateway to the CellGateway to the Cell

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Photograph of a Cell Photograph of a Cell MembraneMembrane

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Cell MembraneCell Membrane

The cell membrane is flexibleflexible and allows a unicellular organism to move

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HomeostasisHomeostasis

•Balanced internal condition of cells

•Also called equilibrium•Maintained by plasma

membrane controlling what enters & leaves the cell

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Functions of Plasma Functions of Plasma MembraneMembrane

Protective barrierProtective barrier

Regulate transport in & out of Regulate transport in & out of cell cell (selectively permeable)(selectively permeable)

Allow cell recognitionAllow cell recognition

Provide anchoring sites for Provide anchoring sites for filaments filaments of cytoskeletonof cytoskeleton

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Structure of the Structure of the Cell MembraneCell Membrane

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PhospholipPhospholipidsids

Proteins

Membrane ComponentsMembrane Components

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PhospholipidsPhospholipids

Make up the cell membrane

Contains 2 fatty acid chains that are nonpolarHead is polar & contains a Phosphate group

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Fluid mosaic model

FLUIDFLUID- because individual phospholipids and - because individual phospholipids and proteins can move around freely within the proteins can move around freely within the layer, like it’s a liquid.layer, like it’s a liquid.

MOSAICMOSAIC- because of the pattern produced by - because of the pattern produced by the scattered protein molecules when the the scattered protein molecules when the membrane is viewed from abovemembrane is viewed from above..

FLUID MOSAIC MODELFLUID MOSAIC MODEL

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Polar heads are hydrophilichydrophilic “water loving”Nonpolar tails are hydrophobichydrophobic “water fearing”

Cell MembraneCell Membrane

Makes membrane “Selective” in what crosses

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Cell MembraneCell Membrane

Hydrophobic molecules pass easily; hydrophillic DO NOT

The cell membrane is made of 2 layers of phospholipidphospholipids called the lipid bilayerbilayer

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SolubilitySolubility•Materials

that are soluble in lipids can pass through the cell membrane easily

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Small non-charged molecules move through easily.Examples: O2, and CO2

Semipermeable Semipermeable MembraneMembrane

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Ions, and large molecules such as glucose and amino acids do not move through the membrane on their own. They must use transport proteins

Semipermeable Semipermeable MembraneMembrane

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Types of Transport Types of Transport Across Cell Across Cell MembranesMembranes

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Simple DiffusionSimple Diffusion

• Requires NONO energy

• Molecules move from area of HIGH HIGH to LOWto LOW concentration

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DIFFUSIONDIFFUSION

Diffusion is a PASSIVEPASSIVE process which means no energy is used to make the molecules move.

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Diffusion of LiquidsDiffusion of Liquids

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Diffusion through a Diffusion through a MembraneMembrane

Cell membrane

Solute moves DOWN concentration gradient (HIGH to LOW)

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OsmosisOsmosis

• Diffusion of Diffusion of waterwater across a across a membranemembrane

• Moves from Moves from HIGH HIGH Concentration Concentration to a to a LOW LOW concentrationconcentration

Diffusion across a membrane

Semipermeable

membrane

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Cell in Isotonic SolutionCell in Isotonic Solution

CELLCELL

10% NaCL90% H2O

10% NaCL

90% H2O

What is the direction of water movement?The cell is at _______________.equilibrium

ENVIRONMENTENVIRONMENT

NO NET NO NET MOVEMENMOVEMENTT

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Cell in Hypotonic Cell in Hypotonic SolutionSolution

CELLCELL

10% NaCL90% H2O

20% NaCL

80% H2O

What is the direction of water movement?

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Cell in Hypertonic Cell in Hypertonic SolutionSolution

CELLCELL

15% NaCL85% H2O

5% NaCL95% H2O

What is the direction of water movement?

ENVIRONMENTENVIRONMENT

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Cells in SolutionsCells in Solutions

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Osmosis in Red Blood Osmosis in Red Blood CellsCells

IsotonicIsotonic Hypotonic

Hypertonic

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Three Forms of Transport Across the MembraneThree Forms of Transport Across the Membrane

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Passive Passive TransportTransport

Simple DiffusionSimple Diffusion

Doesn’tDoesn’t require require energyenergy

Moves Moves high to lowhigh to low concentrationconcentration Example: Example: OxygenOxygen diffusing in or diffusing in or carbon carbon dioxidedioxide diffusing out diffusing out.

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Passive Passive TransportTransport

Facilitated diffusion

Doesn’t require energy

Uses transport proteins to move high to low concentrationExamples: Glucose or Examples: Glucose or amino acids moving amino acids moving from blood into a from blood into a cell.cell.

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Proteins Are Critical to Proteins Are Critical to Membrane FunctionMembrane Function

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Active TransportActive Transport

Requires energy or ATP

Moves materials from LOW to HIGH concentration

AGAINST concentration gradient

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Active transportActive transportSodium-Sodium-

Potassium PumpPotassium PumpExamples:

Pumping Na+ (sodium ions) out and K+ (potassium ions) in against strong concentration gradients.

Called Na+-K+ Pump

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Sodium-Potassium Sodium-Potassium PumpPump

3 Na+ pumped in for every 2 K+ pumped out; creates a membrane

potential

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Moving the “Big Stuff”Moving the “Big Stuff”

Molecules are Molecules are moved outmoved out of the cell by of the cell by vesiclesvesicles that that fusefuse with the plasma membrane. with the plasma membrane.

ExocytosExocytosisis-

moving things out.

This is how many This is how many hormoneshormones are secreted and how are secreted and how nerve cellsnerve cells communicate with one another communicate with one another.

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ExocytosisExocytosisExocytic Exocytic vesicle vesicle immediately immediately after fusion after fusion with plasma with plasma membrane.membrane.

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Moving the “Big Moving the “Big Stuff”Stuff”Large molecules move materials into the Large molecules move materials into the

cell by one of cell by one of three forms of endocytosisthree forms of endocytosis.

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PinocytosisPinocytosis

Most Most commoncommon form of endocytosis form of endocytosis. Takes in Takes in dissolveddissolved molecules as a molecules as a vesiclevesicle.

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PinocytosisPinocytosis

• Cell forms an Cell forms an invaginationinvagination

• Materials Materials dissolve in dissolve in waterwater to be to be brought into brought into cellcell

• Called Called “Cell “Cell Drinking”Drinking”

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Example of Example of PinocytosisPinocytosispinocytic vesicles forming mature transport vesicle

Transport across a capillary cell (blue).

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Receptor-Mediated EndocytosisReceptor-Mediated Endocytosis

Some Some integral proteinsintegral proteins have have receptorsreceptors on their surface to on their surface to recognize & take in recognize & take in hormones, hormones, cholesterolcholesterol, etc., etc.

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Receptor-Mediated EndocytosisReceptor-Mediated Endocytosis

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Endocytosis – Phagocytosis Endocytosis – Phagocytosis

Used to Used to engulf large particlesengulf large particles such such as food, as food, bacteriabacteria, etc. into vesicles, etc. into vesicles

Called Called “Cell Eating”“Cell Eating”

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Phagocytosis About to OccurPhagocytosis About to Occur

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PhagocytoPhagocytosissis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue)

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ExocytosisExocytosis The opposite of endocytosis is exocytosis. The opposite of endocytosis is exocytosis. Large moleculesLarge molecules that are manufactured in that are manufactured in

the cell are the cell are releasedreleased through the cell through the cell membranemembrane..

Inside Cell Cell environment

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The End