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!