The Cell MembraneThe Cell Membrane

1 Gateway Across the Gateway Across the CellCell

Functions of Plasma Functions of Plasma MembraneMembrane

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Protective barrierProtective barrier

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

Importance of the Cell Membrane

Maintains HOMEOSTASIS

Balanced internal condition of cells…this is called reaching equilibrium

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Structure of the Cell Structure of the Cell MembraneMembrane

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Phospholipid BilayerPhospholipid Bilayer

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• Contains 2 lipid tails that are hydrophobic (nonpolar)• Phosphate head is hydrophilic (polar)

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Cell MembraneCell Membrane

Polar heads are hydrophilichydrophilic “water loving”Nonpolar tails are hydrophobichydrophobic “water fearing”Makes membrane “Selective” in what crosses

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

MOSAICMOSAIC- - because of the pattern produced by the because of the pattern produced by the scattered protein molecules when the scattered protein molecules when the membrane is viewed from above.membrane is viewed from above.7

FLUID MOSAIC MODELFLUID MOSAIC MODEL

Selective PermeabilitySelective Permeability

Definition: the cell membrane only allows some, but not all, molecules to cross it

Also called semipermeable

Enables cells to maintain homeostasis

How molecules cross the cell membrane depend on it’s size and polarity

Sometimes ENERGY is needed (ACTIVE transport), other times ENERGY is NOTNOT needed (PASSIVE transport)

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Types of Transport Types of Transport Across Cell Across Cell MembranesMembranes

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Passive Transport

Passive transport—movement of molecules across the cell membrane WITHOUT the use of energy

3 types:

Diffusion

Osmosis

Facilitated diffusion10

DiffusionRequires NONO

energy

Molecules move from an area of HIGHHIGH concentration to to LOWLOW concentration

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Cell membrane

Solutes move DOWN concentration gradient

(HIGH to LOW)

OsmosisOsmosisDiffusion of Diffusion of

waterwater across a across a membranemembrane

Moves from Moves from HIGH water HIGH water potential (low potential (low solute) to LOW solute) to LOW water potential water potential (high solute)(high solute)13

Diffusion across a membrane

Semipermeable

membrane

Diffusion of Water Across A Diffusion of Water Across A MembraneMembrane

14High H2O potentialLow solute concentration

Low H2O potentialHigh solute concentration

Cell in Isotonic SolutionCell in Isotonic Solution

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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

Cell in Hypotonic SolutionCell in Hypotonic Solution

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CELLCELL

10% NaCL90% H2O

20% NaCl80% H2O

What is the direction of water movement?

Cell in Hypertonic Solution

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CELLCELL

15% NaCL85% H2O

5% NaCL95% H2O

What is the direction of water movement?

ENVIRONMENTENVIRONMENT

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Isotonic Solution

NO NET MOVEMENT OF

H2O (equal amounts entering

& leaving)

Hypotonic Solution

CYTOLYSIS

Hypertonic Solution

PLASMOLYSIS

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Facilitated diffusion

Doesn’t require energy

Uses transport proteins to move high to low concentration

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Active TransportActive Transport

Requires energy or ATP

Moves materials from LOW to HIGH concentration

AGAINST concentration gradient

Active transport

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

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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 fuse with the plasma membrane.that fuse with the plasma membrane.

ExoExocytoscytosisis-

moving moving things things out.out.

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Endocytosis – Phagocytosis Endocytosis – Phagocytosis

Used to Used to engulf large particlesengulf large particles such as such as food, bacteria, etc. food, bacteria, etc. intointo vesicles vesicles