biology sylvia s. mader michael windelspecht chapter 5 membrane structure and function lecture...
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BiologySylvia S. Mader
Michael Windelspecht
Chapter 5 Membrane Structure
and FunctionLecture Outline
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Outline
• 5.1 Plasma Membrane Structure and Function
• 5.2 Passive Transport Across a Membrane
• 5.3 Active Transport Across a Membrane
• 5.4 Modification of Cell Surfaces
5.1 Plasma Membrane Structure and Function
• The plasma membrane is common to all cells
• Separates: Internal cytoplasm from the external environment of
the cell
• Phospholipid bilayer: * * Nonpolar, hydrophobic, fatty-acid tails sandwiched in
between
3
Plasma Membrane Structure and Function
• Components of the Plasma Membrane Three components:
• *• *
– Float around like icebergs on a sea– Membrane proteins may be peripheral or integral
» Peripheral proteins are found on the inner membrane surface
» Integral proteins are partially or wholly embedded (transmembrane) in the membrane
• *
4
Membrane Proteins
5
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hydrophobicregion
phospholipid
Water outside cell
integralprotein
hydrophilicregions
Water inside cell
peripheralproteins
cholesterol
Plasma Membrane Structure and Function
• Carbohydrate Chains Glycoproteins
• Proteins with attached carbohydrate chains Glycolipids
• Lipids with attached carbohydrate chains *
• Makes the membrane asymmetrical
6
Plasma Membrane of an Animal Cell
7
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Plasma membrane
filaments of cytoskeleton Inside cell
integral protein
cholesterol
peripheral protein
glycolipid
carbohydratechain Outside cell
hydrophilicheads
phospholipid
glycoprotein
extracellularMatrix (ECM)
phospholipidbilayer
hydrophobictails
Plasma Membrane Structure and Function
• Functions of Membrane Proteins *:
• Allow passage of molecules through membrane via a channel in the protein
*:• Combine with the substance to be transported• Assist passage of molecules through membrane
*:• Glycoproteins• Help the body recognize foreign substances
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Plasma Membrane Structure and Function
• Functions of Membrane Proteins (continued) *:
• Bind with specific molecules• Allow a cell to respond to signals from other cells
*:• Carry out metabolic reactions directly
*:• Attach adjacent cells
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Channel Protein:Allows a particularmolecule or ion tocross the plasmamembrane freely.Cystic fibrosis, aninherited disorder,is caused by afaulty chloride (Cl–)channel; a thickmucus collects inairways and inpancreatic and liver ducts.
a.
Membrane Protein Diversity
b.
Carrier Protein:
Selectively interacts
with a specific
molecule or ion so
that it can cross the
plasma membrane.
The inability of some
persons to use
energy for sodium-
potassium (Na+–K+)
transport has been
suggested as the
cause of their obesity.
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Cell RecognitionProtein:The MHC (majorhistocompatibilitycomplex) glycoproteinsare different for eachperson, so organtransplants are difficultto achieve. Cells withforeign MHCglycoproteins areattacked by white bloodcells responsible forimmunity.
c.
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Receptor Protein:Is shaped in such away that a specificmolecule can bind toit. Pygmies are short,not because they donot produce enoughgrowth hormone, butbecause their plasmamembrane growthhormone receptorsare faulty and cannotinteract with growthhormone.
d.
Enzymatic Protein:Catalyzes a specificreaction. The membraneprotein, adenylatecyclase, is involved inATP metabolism. Cholerabacteria release a toxinthat interferes with theproper functioning ofadenylate cyclase;sodium (Na+) and waterleave intestinal cells, andthe individual may diefrom severe diarrhea.
e.
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Junction Proteins:
Tight junctions join
cells so that a tissue
can fulfill a function, as
when a tissue pinches
off the neural tube
during development.
Without this
cooperation between
cells, an animal
embryo would have no
nervous system.f.
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Channel Protein:Allows a particularmolecule or ion tocross the plasmamembrane freely.Cystic fibrosis, aninherited disorder,is caused by afaulty chloride (Cl–)channel; a thickmucus collects inairways and inpancreatic andliver ducts.
Carrier Protein:Selectively interactswith a specificmolecule or ion sothat it can cross theplasma membrane.The inability of somepersons to useenergy for sodium-potassium (Na+–K+)transport has beensuggested as thecause of their obesity.
Receptor Protein:Is shaped in such away that a specificmolecule can bind toit. Pygmies are short,not because they donot produce enoughgrowth hormone, butbecause their plasmamembrane growthhormone receptorsare faulty and cannotinteract with growthhormone.
Enzymatic Protein:Catalyzes a specificreaction. The membraneprotein, adenylatecyclase, is involved inATP metabolism. Cholerabacteria release a toxinthat interferes with theproper functioning ofadenylate cyclase;sodium (Na+) and waterleave intestinal cells, andthe individual may diefrom severe diarrhea.
Junction Proteins:Tight junctions joincells so that a tissuecan fulfill a function, aswhen a tissue pinchesoff the neural tubeduring development.Without thiscooperation betweencells, an animalembryo would have nonervous system.
Cell RecognitionProtein:The MHC (majorhistocompatibilitycomplex) glycoproteinsare different for eachperson, so organtransplants are difficultto achieve. Cells withforeign MHCglycoproteins areattacked by white bloodcells responsible forimmunity.
a. b.
d. e.
c.
f.
Membrane Protein Diversity
How Cells Talk to One Another
• *
Cell receptors bind to specific signaling molecules
Once the signaling molecule and the cell receptor bind a cascade of events occurs that elicits a cellular response
• Signal transduction pathway
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Cell Signaling
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Cellularresponse:
Altered shapeor movementof cell
Alteredmetabolismor cellularfunction
Altered geneexpressionand the typesand amountof proteinsproduced
generegulatory
protein
Nucleus
b.
Cytoplasm
unactivatedreceptorprotein
Nuclearenvelope
enzyme
structuralprotein
receptoractivation
signalingmolecule
Targetedprotein:plasma
membrane
newborna. egg embryo
Left: © Anatomical Travelogue/Photo Researchers, Inc.; Middle: © Neil Harding/Stone/Getty Images; Right: © Photodisc Collection/Getty RF
2.Transduction pathway: Series of relay proteins that ends when a protein is activated.
3. Response: Targeted protein(s) bring about a cellular response.
1. Receptor: Binds to a signaling molecule, becomes activated and initiates a transduction pathway.
Plasma Membrane Structure and Function
• Permeability of the Plasma Membrane The plasma membrane is *
• Allows some substances to move across the membrane
• Inhibits passage of other molecules
Small, non-charged molecules (CO2, O2, glycerol, alcohol) freely cross the membrane by passing through the phospholipid bilayer
• These molecules follow their concentration gradient
– *.
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Plasma Membrane Structure and Function
• Permeability of the Plasma Membrane Water moves across the plasma membrane
• Specialized proteins termed *
The movement of ions and polar molecules across the membrane is often assisted by carrier proteins
Some molecules must move against their concentration gradient with the expenditure of energy
• *
Large particles enter or exit the cell via bulk transport• *
• *
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How Molecules Cross the Plasma Membrane
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water inside cell phospholipidmolecule
protein
water outside cell
nonpolar,
hydrophobic core
How Molecules Cross the Plasma Membrane
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+
–+
water inside cell phospholipidmolecule
protein
water outside cell
charged moleculesand ions–
nonpolar,
hydrophobic core
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How Molecules Cross the Plasma Membrane
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+
–+
water inside cell phospholipidmolecule
protein
charged moleculesand ions
H2O
–
nonpolar,
hydrophobic core
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How Molecules Cross the Plasma Membrane
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+
–+
water inside cell phospholipidmolecule
protein
nonchargedmolecules
water outside cell
charged moleculesand ions
H2O
–
nonpolar,
hydrophobic core
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How Molecules Cross the Plasma Membrane
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+
–+
water inside cell phospholipidmolecule
protein
macromolecule
nonchargedmolecules
water outside cell
charged moleculesand ions
H2O
–
nonpolar,
hydrophobic core
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Passage of Molecules Into and out of the Cell
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5.2 Passive Transport Across a Membrane
• A solution consists of: A * A *
• Diffusion Net movement of molecules down a concentration
gradient Molecules move both ways along gradient, but net
movement is from high to low concentration Equilibrium:
• *• Solute concentration is uniform – no gradient
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Process of Diffusion
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crystaldye
a. Crystal of dye is placed in water
Process of Diffusion
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time
crystaldye
a. Crystal of dye is placed in water b. Diffusion of water and dye molecules
Process of Diffusion
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time time
crystaldye
a. Crystal of dye is placed in water b. Diffusion of water and dye molecules c. Equal distribution of molecules results
Gas Exchange in Lungs
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O2
oxygen
O2
O2
O2
O2
O2
O2
O2
O2O2
O2
O2
O2
O2
highO2
concentrationlowO2
concentration
bronchiole
capillaryalveolus
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Passive Transport Across a Membrane
• Osmosis: Special case of diffusion Focuses on solvent (water) movement rather than
solute Diffusion of water across a selectively permeable
membrane• *• *
Water can diffuse both ways across membrane but the solute cannot
Net movement of water is toward low water (high solute) concentration
• Osmotic pressure is *
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Osmosis Demonstration
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a.
less water (higherpercentage of solute)
more water (lowerpercentage of solute)
10%
5%
<10%
>5%
solute
differentiallypermeablemembrane
water
b.
c.
less water (higherpercentage of solute)
more water (lowerpercentage of solute)
beaker
thistletube
Passive Transport Across a Membrane
• Isotonic Solutions * No net gain or loss of water by the cell
• Hypotonic Solutions * Cells placed in a hypotonic solution will swell
• Causes turgor pressure in plants• May cause animal cells to lyse (rupture)
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Passive Transport Across a Membrane
• Hypertonic Solutions * Cells placed in a hypertonic solution will
shrink • Crenation in animal cells• Plasmolysis in plant cells
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Osmosis in Animal and Plant Cells
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In a hypertonic solution, watermainly leaves the cell, whichshrivels (crenation).
In a hypertonic solution, vacuoleslose water, the cytoplasm shrinks(plasmolysis), and chloroplastsare seen in the center of the cell.
In a hypotonic solution, vacuolesfill with water, turgor pressuredevelops, and chloroplasts areseen next to the cell wall.
In an isotonic solution, there is nonet movement of water.
In an isotonic solution, there is no netmovement of water.
In a hypotonic solution, watermainly enters the cell, which mayburst (lysis).
plasmamembrane
Animalcells
nucleus
Plantcells
centralvacuole
chloroplast
nucleus
cellwall
plasmamembrane
Passive Transport Across a Membrane
Facilitated Transport• *
• These molecules must combine with carrier proteins to move across the membrane
• Follow concentration gradient, moving from high concentration to low concentration
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solute
Outside
Inside
plasma membrane
carrier protein
Facilitated Transport
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solute
Outside
Inside
plasmamembrane
carrier protein
Facilitated Transport
solute
Outside
Inside
plasma membrane
carrier protein
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Facilitated Transport
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solute
Outside
Inside
plasma membrane
carrier protein
Facilitated Transport
5.3 Active Transport Across a Membrane
Active Transport• *
– Movement from low to high concentration
• Movement is facilitated by carrier proteins
• *
• Ex: sodium-potassium pump– Uses ATP to move sodium ions out of the cells and
potassium ions into the cell against their concentration gradients.
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The Sodium-Potassium Pump
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carrierprotein
1. Carrier has a shape that allowsit to take up 3 Na+
Outside
Inside
K+
K+
Na+
K+
K+
Na+
Na+ Na+
Na+
The Sodium-Potassium Pump
44
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carrier
protein
1. Carrier has a shape that allowsit to take up 3 Na+.
2. ATP is split, and phosphategroup attaches to carrier
Outside
Inside
ATP
K+
P
Na+
Na+
K+
K+
K+K+
K+
Na+Na+ Na+
Na+
K+
K+
Na+
Na+
Na+
The Sodium-Potassium Pump
45
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carrierprotein
1. Carrier has a shape that allowsit to take up 3 Na+.
3. Change in shape results andcauses carrier to release 3 Na+
outside the cell.
Outside
Inside
ATP
K+
K+
K+
P
P
Na+
Na+
Na+
Na+
K+
K+
K+
Na+
Na+ Na+
K+ K+
K+
Na+
Na+
Na+
Na+
2. ATP is split, and phosphategroup attaches to carrier
K+
Na+Na+
K+
K+
Na+
The Sodium-Potassium Pump
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carrierprotein
1. Carrier has a shape that allowsit to take up 3 Na+.
4. Carrier has a shape thatallows it to take up 2K+.
3. Change in shape results andcauses carrier to release 3 Na+
outside the cell.
Outside
Inside
ATP
K+
K+
K+
K+
K+
K+
K+
K+
P
P
P
Na+Na+
Na+
Na+
Na+
Na+
Na+
K+
K+
K+
Na+
Na+ Na+
Na+
Na+
Na+
Na+
Na+
Na+
K+K+
K+
2. ATP is split, and phosphategroup attaches to carrier.
K+
Na+Na+
K+
Na+
Na+
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The Sodium-Potassium Pump
47
carrierprotein
1. Carrier has a shape that allowsit to take up 3 Na+.
4. Carrier has a shape thatallows it to take up 2 K+.
2. ATP is split, and phosphategroup attaches to carrier.
3. Change in shape results andcauses carrier to release 3 Na+
outside the cell.
5. Phosphate group is releasedfrom carrier.
Outside
Inside
ATP
K+
K+
K+
K+P
P
P
P
Na+
Na+
Na+
Na+Na+
Na +
Na+
Na+
Na +
Na+
Na+
K+
K+K+
Na+
Na+ Na+
Na+
K+K+
K+
Na+
Na+
Na+
Na+
K+K+
K+
Na+
K+
K+
K+
Na+Na+
K+
K+
Na+
Na+
K+
K+
Na+
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The Sodium-Potassium Pump
48
carrierprotein
1. Carrier has a shape that allowsit to take up 3 Na+.
4. Carrier has a shape thatallows it to take up 2 K+.
2. ATP is split, and phosphategroup attaches to carrier.
3. Change in shape results andcauses carrier to release 3 Na+
outside the cell.
5. Phosphate group is releasedfrom carrier.
Outside
Inside
ATP
K+
K+
K+
K+P
P
P
P
Na+
Na+
Na+
Na+Na+
Na +
Na+
Na+
Na +
Na+
Na+
K+
K+K+
Na+
Na+ Na+
Na+
K+K+
K+
Na+
Na+
Na+
Na+
K+K+
K+
Na+
K+
K+
K+
Na+Na+
K+
K+
Na+
Na+
K+
K+
Na+
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6. Change in shape results andcauses carrier to release 2K+
inside the cell.
K+
K
K+
Na+
Na+
Na +
Na+ Na+
K+
Active Transport Across a Membrane
• Macromolecules are transported into or out of the cell inside vesicles via bulk transport Exocytosis – *
Endocytosis – *• Phagocytosis – Large, solid material is taken in by
endocytosis
• Pinocytosis – Vesicles form around a liquid or very small particles
• Receptor-Mediated Endocytosis– Specific form of pinocytosis using receptor proteins and a coated pit
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Exocytosis
50
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OutsidePlasma membrane
Insidesecretoryvesicle
Three Methods of Endocytosis
51
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pseudopod
paramecium
vacuoleforming
vesiclesforming
coatedpit
coatedvesicle
solute
solute
a. Phagocytosis
b. Pinocytosis
vacuole
coated vesicle
plasma membrane
receptor protein
coated pit
c. Receptor-mediated endocytosis
vesicle
0.5 μm
399.9 μm
Animation
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5.4 Modifications of Cell Surfaces
• Cell Surfaces in Animals
Extracellular Matrix (ECM)
• *
– Collagen – resists stretching
– Elastin – provides resilience to the ECM
– Integrin – play role in cell signaling
– Proteoglycans – regulate passage of material through the ECM to the plasma membrane
53
Animal Cell Extracellular Matrix
54
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collagenproteoglycan
actin filament
fibronectin
elastin
integrin
Outside (extracellular matrix)
Inside (cytoplasm)
Modifications of Cell Surfaces
• Cell Surfaces in Animals
Junctions Between Cells
• Adhesion Junctions - Intercellular filaments between cells
– Desmosomes – internal cytoplasmic plaques
– Tight Junctions – form impermeable barriers
• Gap Junctions
– Plasma membrane channels are joined (allows communication)
55
Junctions Between Cells of the Intestinal Wall
56
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plasmamembranescytoplasmic
plaque
Filamentsofcytoskeleton
adhesionproteins
intercellularspace
a. Adhesion junction
b. Tight junction
c. Gap junction
plasmamembranes
light junctionproteins
intercellularspace
plasmamembranes
intercellularspace
membranechannels
a: From Douglas E. Kelly, J. Cell Biol. 28 (1966): 51. Reproduced by copyright permission of The Rockefeller University Press; b: © David M. Phillips/Visuals Unlimited;c: Courtesy Camillo Peracchia, M.D.
20 nm
50 nm
100 nm
Modifications of Cell Surfaces
• Plant Cell Walls Plants have a freely permeable cell wall, with
cellulose as the main component• Plasmodesmata penetrate the cell wall
• Each contains a strand of cytoplasm
• Allow passage of material between cells
57
Plasmodesmata
58
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cell wall
plasmodesmata
cell wall
Cell 1 Cell 2
plasmamembrane
cell wall cell wall
cytoplasm
plasmamembrane
cytoplasm
middle lamella
plasmodesmata
0.3mm
© E.H. Newcomb/Biological Photo Service