The AmazingThe AmazingPlasma MembranePlasma Membrane

Structure and FunctionStructure and Function

Overview of functionsOverview of functions

►Container—holds the cytoplasm & Container—holds the cytoplasm & organelles inorganelles in

►Protective barrierProtective barrier►Allows cell to cell communicationAllows cell to cell communication►Gatekeeper—regulates what goes in Gatekeeper—regulates what goes in

and out of the cell*and out of the cell*

How???How???

►How does it determine what should come How does it determine what should come in, what should go out?in, what should go out?

►How does it determine how much of How does it determine how much of something should come in, go out?something should come in, go out?

►How does it let them in and out, while How does it let them in and out, while not letting other things in and out as not letting other things in and out as well?well?

StructureStructure

►PhospholipidPhospholipid bilayer bilayer

What is a phospholipid?What is a phospholipid?previously: previously: lipid = glycerol + 3 fatty acidslipid = glycerol + 3 fatty acids (long chains of C, H, O)(long chains of C, H, O)

phospho = phosphate POphospho = phosphate PO44

Phospholipid propertiesPhospholipid properties

Phosphate end: polar, hydrophilicPhosphate end: polar, hydrophilic

Lipid end (now only 2 fatty acids): nonpolar, Lipid end (now only 2 fatty acids): nonpolar, hydrophobichydrophobic

Phospholipid Phospholipid bilayerbilayer

Bi- = twoBi- = two► Double layer of phospholipidsDouble layer of phospholipids► Oriented so hydrophilic ends are near water Oriented so hydrophilic ends are near water

and hydrophobic ends are away from waterand hydrophobic ends are away from water

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Another lookAnother look

Membrane is semipermeable

In Out

Nonpolar, hydrophobic Ex: O2, N2, lipids

Polar, hydrophilic Ex: glucose, fructose

Small

Ex: H2O, CO2

Large Ex: macromolecules

Uncharged

Ex: urea, ethanol

Charged Ex: Ions

H+, Na+, K+, Cl-

But cells need those other But cells need those other molecules—so how do they get molecules—so how do they get in?in?►Proteins embedded in the phospholipid Proteins embedded in the phospholipid

bilayerbilayer

They act as channelsThey act as channels

and play other and play other

important roles important roles

as wellas well

FLUID- because individual phospholipids and FLUID- because individual phospholipids and proteins can proteins can movemove within the layer within the layer

MOSAIC- because of the patchwork pattern MOSAIC- because of the patchwork pattern produced by the scattered protein moleculesproduced by the scattered protein molecules

FLUID MOSAIC MODELFLUID MOSAIC MODEL

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ReviewReview

►What is the basic structure of the What is the basic structure of the plasma membrane?plasma membrane?

►Why does it form a bilayer?Why does it form a bilayer?►What does it mean to say the membrane What does it mean to say the membrane

is semipermeable (or selectively is semipermeable (or selectively permeable)?permeable)?

►So how does anything else get through?So how does anything else get through?►What is the fluid mosaic model?What is the fluid mosaic model?

FunctionFunction

Transport of materials across the Transport of materials across the membranemembrane

Passive transportPassive transport Active transportActive transport

No Energy Required!No Energy Required! Energy Energy Required!Required!

Passive transportPassive transport

►DiffusionDiffusion►Facilitated DiffusionFacilitated Diffusion►OsmosisOsmosis

Equilibrium (everything is balanced)

Simple DiffusionSimple Diffusion

Cell membrane

Solute moves DOWN concentration gradient

from area of HIGH concentration (many molecules per mL) to area of LOW concentration (fewer

molecules per mL)

Diffusion through a membrane

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Random movementRandom movement

► In diffusion, solute molecules move In diffusion, solute molecules move randomly, bumping into each other as they randomly, bumping into each other as they go.go.

► Through random movement, they spread Through random movement, they spread out to every corner of the space.out to every corner of the space.

► EquilibriumEquilibrium is reached when the molecules is reached when the molecules are evenly spread throughout the space. are evenly spread throughout the space. However, they continue to move—there is However, they continue to move—there is just no net change in concentration.just no net change in concentration.

Two tasks-simultaneously► Two of you set up diffusion activity► The other two set up for egg osmosis lab:1. Get a scale, 2 beakers, 100 mL graduated

cylinder, 2 strips of masking tape, piece of string, ruler, sheet of paper.

2. Use masking tape to label one beaker A and the other B and put your initials on both labels

3. Weigh Beaker A and record weight4. Get egg from Ms. Z: use string to measure egg

around its widest point and record5. Put it gently into beaker A and record new

weight6. Measure 100 mL of vinegar and pour into beaker7. Repeat with Beaker B

Facilitated diffusionFacilitated diffusion

FacilitatedFacilitated = helped = helped

Some molecules are helped by Some molecules are helped by channelchannel or or carriercarrier proteins proteins

►Channel – a tunnel for substances like Channel – a tunnel for substances like glucoseglucose

Facilitated diffusionFacilitated diffusion

► CarrierCarrier protein – changes shape to facilitate protein – changes shape to facilitate molecule passing throughmolecule passing through

Facilitated diffusion also involves moving Facilitated diffusion also involves moving across a concentration gradient (from high to across a concentration gradient (from high to low)—like diffusion, does not require energylow)—like diffusion, does not require energy

OsmosisOsmosis

Osmosis = diffusion of water through a Osmosis = diffusion of water through a cell membranecell membrane

Definition: the movement of water from Definition: the movement of water from a region of high water potential (low a region of high water potential (low solute concentration) to low water solute concentration) to low water potential (high solute concentration)potential (high solute concentration)

Osmosis: Diffusion of Osmosis: Diffusion of WaterWater

Three osmotic conditions

► Isotonic: iso = the same --two solutions have the same solute concentration--so the water flow between them is in equilibrium

For example, if one solution is a cell and the other solution is the surrounding environment, they have the same salt concentration

Cell in Isotonic SolutionCell in Isotonic Solution

CELLCELL

10% NaCL90% H2O

10% NaCL

90% H2O

ENVIRONMENTENVIRONMENT

NO NET NO NET MOVEMENMOVEMENTT

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

Three osmotic conditions

► Hypertonic: hyper = higher than--comparing two solutions, the one with a higher solute concentration is hypertonic to the other: it will gain water --so water will flow into the hypertonic solution

For example, if the outside environment has a higher salt concentration than inside the cell, the outside environment is hypertonic to the cell: water will flow out of the cell and the cell will shrink

Cell in Hypertonic SolutionCell in Hypertonic Solution

CELLCELL

15% NaCL85% H2O

5% NaCL95% H2O

What is the direction of water movement?

ENVIRONMENTENVIRONMENT

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Three osmotic conditions

► Hypotonic: hypo- = lower than--comparing two solutions, the one with the lower solute concentration is hypotonic to the one with higher solute concentration: it will lose water--so water will flow out of the hypotonic solution

For example, if the outside environment has a lower salt concentration than inside the cell, then the outside is hypotonic to the cell: water will flow into the cell and the cell will swell

Cell in Hypotonic SolutionCell in Hypotonic Solution

CELLCELL

10% NaCL90% H2O

20% NaCL

80% H2O

What is the direction of water movement? copyright cmassengale

What is the direction of water movement?

Three osmotic conditionsThree osmotic conditions

Isotonic: the same amount of water leaves the cell as enters

Hypotonic: the pure water solution loses water to the red blood cell, which expands

Hypertonic: the red blood cell loses water to the salt solution, causing it to shrink

TonicityTonicity

Cells in SolutionsCells in Solutions

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Cytolysis & PlasmolysisCytolysis & Plasmolysis

Cytolysis Plasmolysis

ReviewReview

► How is passive transport different from active How is passive transport different from active transport?transport?

► What are the three types of passive What are the three types of passive transport?transport?

► What is an example of diffusion?What is an example of diffusion?► In facilitated diffusion, what does the In facilitated diffusion, what does the

facilitating and how does it do it?facilitating and how does it do it?► How is osmosis different from diffusion?How is osmosis different from diffusion?► How are hypotonic, isotonic, and hypertonic How are hypotonic, isotonic, and hypertonic

conditions different?conditions different?

Active Transport

►Requires energy -- why?Because it is moving materials against a

concentration gradient: from low to high concentration instead of from high to low

Ion pump

►Example: Sodium-Potassium pumpProteins in membrane change conformation to

pump sodium ions (Na+) in one direction and potassium ions (K+) in the other direction

Endocytosis and Exocytosis

Sometimes the cell has to move big stuff!

Exo- = out: move it outEndo- = in: move it in

For example, this is how hormones are sent out

Endocytosis

►Phagocytosis-cell eating►Pinocytosis-cell drinking►Receptor-mediated endocytosis

PhagocytosisPhagocytosis

Projections from the membrane called pseudopods (false feet) surround and engulf an external object.

In this picture the cell is “eating” a bacterium.

PinocytosisPinocytosis

►This time the This time the membrane membrane pinches in to pinches in to surround an surround an object and forms object and forms a vesicle around a vesicle around it.it.

Receptor mediated Receptor mediated endocytosisendocytosis

Only molecules that are specifically recognized by the receptors in a particular region of the membrane are taken up and enclosed in a coated vesicle.

Other membrane functionsOther membrane functions

Carried out by membrane proteinsCarried out by membrane proteins►Cell to cell recognition (important in Cell to cell recognition (important in

forming tissues)forming tissues)►Cell signaling: hormone binds to Cell signaling: hormone binds to

membrane protein causing it to change membrane protein causing it to change shape and relay signal inside the cellshape and relay signal inside the cell

►Enzyme activity related to plasma Enzyme activity related to plasma membranemembrane