Cell Membrane Cell Membrane Structure and Structure and

FunctionFunction

Lecture #16Lecture #16

Ms. DayMs. Day

Honors BiologyHonors Biology

What is the CellWhat is the CellMembrane?Membrane?

separates living cell from its environment

Controls what substances can Controls what substances can cross into cell cross into cell

Also called the phospholipid bilayer or plasma membrane

The plasma membrane exhibits The plasma membrane exhibits selective selective permeabilitypermeability. It is semi-permeable.which means it lets only certain things into the which means it lets only certain things into the

cell cell

Wow…it’s so

detailed!

Cellular membranes are made of 2 MAIN components

(pieces)

Phospholipids (LIPID)Phospholipids (LIPID)most abundantmost abundant lipid lipid

in membranein membraneThey are They are

amphipathicamphipathic have both hydrophobic have both hydrophobic

and hydrophilic regionsand hydrophilic regions

Phospholipid BilayerPhospholipid Bilayer Phosphate Groups in

“head” (- charge) 2 Fatty Acids in “tail”

(hydrocarbon)

Figure 7.2

HydrophilicHydrophilicheadheadHydrophobicHydrophobictailtail

WATER

WATER

NO WATER

Proteins

Membrane movement animation

Polar heads love water & dissolve.

Non-polar tails “hide” from water.

Carbohydrate cell markers

Fluid Mosaic Model of the cell membrane

The Fluidity of MembranesThe Fluidity of MembranesPhospholipids in the plasma membrane

Can move within the bilayerProteins are larger & drift (move) less

Figure 7.5 A

Lateral movement(~107 times per second)

Flip-flop(~ once per month)

(a) Movement of phospholipids

Another view…Another view…

lower temps lower temps lowers lipid movement lowers lipid movement lowers fluidity lowers fluidity

What 2 things help the cell membrane from freezing solid?

1.) some phospholipids need unsaturated fatty acid tails

Figure 7.5 B

Fluid Viscous

Unsaturated hydrocarbontails with kinks

Saturated hydro-Carbon tails

(b) Membrane fluidity

Fluidity is enhanced

2.) the steroid “cholesterol”“cholesterol” stops fatty acid tails from packing together (only in animal cells)

- cholesterol in membrane - cholesterol in membrane hinders (stops) solidification hinders (stops) solidification **acts as a temp “buffer”

(c) Cholesterol within the animal cell membrane

Cholesterol

Glycoprotein

Carbohydrate

Microfilamentsof cytoskeleton Cholesterol Peripheral

proteinIntegral

proteinCYTOPLASMIC SIDE

OF MEMBRANE

EXTRACELLULAR

SIDE OFMEMBRANE

Glycolipid

Membrane Proteins and Their FunctionsMembrane Proteins and Their FunctionsA membraneA membrane

Includes different proteins in bilayerIncludes different proteins in bilayer

Fibers ofextracellularmatrix (ECM)

2 major 2 major types of types of

membrane membrane proteinsproteins

1. Integral (transmembrane) 1. Integral (transmembrane) proteinsproteins

Go through the hydrophobic core of the lipid bilayer

completely span the membrane

AmphipaticEXTRACELLULARSIDE

Figure 7.8

CYTOPLASMICSIDE

Span of 1+

stretches of

Nonpolar amino acids

Wait…what’s that

word for a polar & nonpolar molecule?

2. Peripheral proteinsAre loosely bound to the surfacesurface of

the membrane

Why have Carbohydrates on Cell Membrane proteins?

Cell-cell recognitionHelps distinguishes one type of cell

from anotherIt’s their “ID” tag

Example:

Chapter 7Cell TransportCell Transport

Ms. GaynorMs. Gaynor

AP BiologyAP Biology

Remember…Cell Membranes are FLUID MOSAIC MODELS

LET’S REVIEW THE CELL MEMBRANE

http://www.hippocampus.org/BiologyClick on “Membranes and Transport”

Listen to animation #1 and #2 (8 minutes long)…get ready!!!

Membrane structure LEADS TO selective permeability

A cell must exchange materials with its surroundingsa process controlled by the selectively permeableselectively permeable plasma membrane

Cell TransportMeans moving things INTO and OUT of the cell

Cells need to take in Food, gases, waterGet rid of waste products

(excretion) Give out such useful substances as

hormones and enzymes (secretion).

Permeability and Cell TransportPermeability and Cell TransportHydrophobic (non polar) molecules

Are lipid soluble (can dissolve) can pass through membrane easily

Ex: Hydrocarbons, CO2, O2

Hydrophilic (Polar) moleculesAre NOT lipid soluble (can’t dissolve)

Lipid INsolubleDo not cross membrane easily

Ex: Na+, Cl- , Glucose/ other sugars•NOTE: CHARGED molecules need “help” NOTE: CHARGED molecules need “help” to cross membraneto cross membrane

Types of Cellular Transport

Passive Transport cell do NOT use energy

1. Diffusion

2. Facilitated Diffusion

3. Osmosis

Active Transportcell DOESuse energy

1. Protein Pumps

2. Endocytosis

3. Exocytosis

high

low

This is going to be hard!

high

low

Weee!

Types of Passive Transport

DiffusionDiffusion= tendency for a populationpopulation of molecules (of ANYANY substance) to spread out evenly into available spaceA “net” movement

Ex: Perfume, a fart , tea, food coloring in water

http://www.indiana.edu/~phys215/lecture/lecnotes/lecgraphics/diffusion2.gif http://www.biosci.ohiou.edu/introbioslab/Bios170/diffusion/Diffusion.html http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

DIFFUSION DIFFUSION In absence of other forces…

Molecules move (diffuse) from area of HIGH [ ] to an area of lower [ ]

A.k.a. Molecules move DOWN its OWNOWN concentration gradientthe difference in [ ] of a substance from one area to another

No chemical work (ATP energy) is used diffusion is spontaneous!

Substances diffuse down their Substances diffuse down their OWN concentration gradientOWN concentration gradient

Net diffusion

Net diffusion

Net diffusion

Net diffusion Equilibrium

Equilibrium

Factors Affecting Diffusion

1. Temperature Higher temperature more kinetic

energy molecules move faster (Example: Tea)

2. Pressure Higher pressure molecules move

faster

Effects of Osmosis on Effects of Osmosis on Water BalanceWater Balance

Osmosis The movement of waterwater (water (water

diffusion)diffusion) across a semipermeable membranesemipermeable membraneInvolves the movement of Involves the movement of FREE FREE

water molecules down a water [ ] water molecules down a water [ ] gradientgradientHigh soluteHigh solute low “free” water [ ] low “free” water [ ]

or….or….Low solute Low solute high free water [ ] high free water [ ]

Osmosis is affected by the concentration gradient of dissolved substances (solutes)

Osmosis animation

3 Different Types of Solutions3 Different Types of SolutionsRecall: Recall: SOLUTION = a uniform SOLUTION = a uniform

mixture of 2 or more substancesmixture of 2 or more substances** compare solutions OUTSIDE cell to inside cell** compare solutions OUTSIDE cell to inside cell

1. If a solution is isotonic [solutes] is the same

outside as inside the cell“iso-” means “same”

There will be NONO net movement of water

ISOTONIC SOLUTION

Result: Water moves equally in both directions and the cell remains same size! (Dynamic

Equilibrium)

2. If a solution is hypertonichypertonic [solutes] is greater outside

than inside the cell The cell will lose water and shrivel or wilt

“hyper” means more (high [solute])

Ex: when salinity increases in lake, fish can die!

HYPERTONIC SOLUTION

Result: Water moves from inside the cell into the solution: Cell shrinks (Plasmolysis)!

3.3. If a solution is hypotonichypotonic[solutes] is less outside

than it is inside the cell The cell will gain water and swell (and maybe lyse or burst)

“hypo” means “less” • (low [solute])

Think: Hypo- sounds like hippo…hippos are big & round; cells in hypotonic solutions get big & roundAlso, think “hypo” is “low” meaning “low”

solutes SURROUNDING cell

“Hypo” is LOW!!!

HYP0TONIC SOLUTION

Result: Water moves from the solution to inside the cell): Cell Swells and bursts open

(cytolysis)!

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

• Osmosis Animations for

isotonic, hypertonic, and hypotonic

solutions

Water Balance of Cells with Walls

Cell wallsCell wallsHelp maintain water balance

Cell walls are in:PlantsProkaryotesFungiSome protists

If a plant cell is turgidIt is in a hypotonic environmentIt is very firmA healthy state in most plants

If a plant cell is flaccidIt is in an isotonic or hypertonic

environmentCells are limp

Plasmolysis= when plasma membrane pulls away from cell wall in hypertonic solutions ; causes cell with walls to wilt & can be lethal.

Water balance in cells with wallsWater balance in cells with walls

H2OH2OH2OH2O

Turgid (normal) Flaccid Plasmolyzed

How Organisms Deal with Osmotic Pressure

•Bacteria and plants have cell walls that prevent them from over-expanding.

•In plants the pressure exerted on the cell wall is called tugor pressure.

•A protist like paramecium has contractile vacuoles that collect water flowing in and pump it out to prevent them from bursting.

•Salt water fish pump salt out of their specialized gills so they do not dehydrate.

•Animal cells are bathed in blood. Kidneys keep the blood isotonic by remove excess salt and water.

Types of Passive Transport

#1 #1 Passive TransportDOES NOT require chemical energy

(ATP)Moves DOWN (WITH) [ ] gradient Kinetic energy drives movementKinetic energy drives movement

#2 #2 Active TransportDOES require chemical energy (ATP)Moves AGAINST its [ ] gradient

2 Types of PASSIVE TRANSPORT1. SIMPLE DIFFUSION

**INCLUDES DIFFUSIONUses NO membrane proteinsGOES DOWN

CONCENTRATION GRADIENT (no ATP needed)Molecules move HIGH [ ]low [ ]

Uncharged & lipid-soluble molecules also pass freely through bilayer. solutes move down a

concentration gradient• Examples: CO2, O2…H2O

WAIT!!! Isn’t water polar?

Aquaporinswater is polar but very

smallIt can pass easily through

membrane uses aquaporins Oh…now

I get it!EXTRACELLULARFLUID

AQUAPORINChannel protein

Water CYTOPLASM

2 Types of PASSIVE TRANSPORT2. FACILITATED DIFFUSION. FACILITATED DIFFUSIONneeds a little “help”needs a little “help”Uses help of Uses help of channel or carrier channel or carrier

proteinsproteins GOES DOWN CONCENTRATION GRADIENT (no ATP needed)

Moves Moves POLARPOLAR molecules molecules can can NOT NOT easily pass through easily pass through HYDROPHOBIC region of membrane. HYDROPHOBIC region of membrane. Example: ions, smaller polar molecules (ex: Example: ions, smaller polar molecules (ex:

sugar)sugar)Channel/carrier proteins Channel/carrier proteins specific receptor specific receptor

site for substances they “help.” site for substances they “help.”

Channel proteins-Provide “tunnels”

EXTRACELLULARFLUID

Channel proteinSolute

CYTOPLASM

A channel protein (purple) has a channel through which water molecules or a specific solute can pass.

(a)

• Channel Proteins animations

Carrier proteins-Undergo a subtle change in shape “carry” solute across the membrane

Carrier proteinSolute

2 Types of Passive Transport

Active transportActive transport

Uses energyenergy to move solutes against their [ ] gradients across the cell membraneEnergyEnergy required usually ATPATP

Carrier proteinsCarrier proteins are used…NEVER channel proteinsEx: sodium-potassium pump

Passive vs. Active Passive vs. Active TransportTransport

Figure 7.17

1. PROTEIN PUMPS•Protein Pumps -transport proteins that require energy to do work•Examples:

•Na+/K+ Pumps are important in nerve responses•Antiports and Symports (Cotransport)•H+ (proton) pump

Sodium Potassium Pumps (Active Transport using

proteins)

Protein changes conformational shape to move molecules: this

requires energy!

Cotransport, Proton Pumps and Sodium/Potassium Pumps…

ANIMATIONShttp://highered.mcgraw-hill.com/sites/0072437316/

student_view0/chapter6/animations.html#

•http://www.wisc-online.com/objects/ViewObject.aspx?ID=ap11203

REVIEW OF ACTIVE TRANSPORT…ANIMATIONS

2. Bulk transport across the 2. Bulk transport across the plasma membraneplasma membrane

Occurs by exocytosisexocytosis and endocytosisendocytosis

BOTH MOVE “BIG” BOTH MOVE “BIG” AMOUNTS OF STUFF in OR AMOUNTS OF STUFF in OR

out OF THE CELLout OF THE CELL

ExoExocytosiscytosisIn exocytosisexocytosis

Transport vesicles move to the plasma membrane, fuse with it, and release their contents

“exo-” means “exit”Ex: hormone excretion; nerve cells and transmitters;

removal of wastes

ER

ROUGH ER

Glycolipid

Vesicle

Membrane glycolipid

Secretedprotein

4

1

2

3

GOLGI APPARATUS

EndoEndocytosiscytosisIn endocytosisendocytosis

Cell takes in macromolecules by forming new vesicles from the plasma membrane

“endo-” means “enter”

2 types of Endocytosis2 types of Endocytosis1. Phagocytosis 1. Phagocytosis

“cell eating” Cell engulfs SOLIDS

into vesicle & “digests” it

2. Pinocytosis 2. Pinocytosis (think (think “pin“pineapple juiceeapple juice) )

“cell drinking” Cell engulfs LIQUIDS

into vesicle & “digests” it

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__phagocytosis.html

Endocytosis and Exocytosis Animations

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter6/animations.html#

REVIEW ANIMATIONS

http://www.hippocampus.org/BiologyClick on “Membranes and Transport”

Listen to animation #3 (7 minutes long)

http://www.northland.cc.mn.us/biology/Biology1111/animations/passive3.swfExcellent Review all Passive (simple/facilitated

diffusion) and Active Transport No verbal explanation…you have to read the

tutorial!