lecture 10 the cell membranethe cell membrane. outline ▪review of cell components ▪membrane...
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Lecture 10
The Cell Membrane
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Outline
▪ Review of Cell Components
▪ Membrane Composition– Lipids
– Proteins
▪ Selective Permeability– Transport Proteins
– Passive Transport
– Active Transport
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Overview of the Cell
▪ All organisms are made of cells
▪ The cell is the simplest collection of matter that can be alive
▪ Cell structure is correlated to cellular function
▪ All cells are related by their descent from earlier cells
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Figure 6.8a
ENDOPLASMIC RETICULUM (ER)
RoughER
SmoothER
Nuclearenvelope
Nucleolus
Chromatin
Plasmamembrane
Ribosomes
Golgi apparatus
LysosomeMitochondrion
Peroxisome
Microvilli
MicrotubulesIntermediate filaments
Microfilaments
Centrosome
CYTOSKELETON:
Flagellum NUCLEUS
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Figure 6.15-1
Smooth ER
Nucleus
Rough ER
Plasmamembrane
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Figure 6.15-2
Smooth ER
Nucleus
Rough ER
Plasmamembrane
cis Golgi
trans Golgi
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Figure 6.15-3
Smooth ER
Nucleus
Rough ER
Plasmamembrane
cis Golgi
trans Golgi
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Figure 6.17aa
Outermembrane
Innermembrane
Cristae
Matrix0.1 m
Mitochondria
▪ Present in almost all Eukaryotic cells– RBCs don’t have a nucleus or mitochondria
▪ The steps of cellular respiration occur in the mitochondria– Glycolysis is in the cytoplasm
– Citric Acid Cycle & ETC in mitochondria
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Figure 6.17a
Intermembrane space
Outer
DNA
Innermembrane
Cristae
Matrix
Freeribosomesin themitochondrialmatrix
(a) Diagram and TEM of mitochondrion0.1 m
membrane
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Figure 6.18aa
Stroma
Inner and outermembranes
Granum
1 m
Chloroplasts
▪ Photosynthesis
▪ Contain Chlorophyll – green pigments
▪ A sub category of organelles called Plastids
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Figure 6.18a
RibosomesStroma
Inner and outermembranes
Granum
1 mIntermembrane spaceThylakoid(a) Diagram and TEM of chloroplast
DNA
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Peroxisomes
▪ Specialized metabolic compartment
▪ Produce Hydrogen Peroxide and convert it to water
▪ Perform many different reactions
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Cell Membrane - Composition
▪ Made up of phospholipids and proteins
▪ Amphipathic molecules – have both hydrophobic and hydrophilic regions
▪ The membrane is a fluid (moving) structure with proteins embedded in it– Mosaic – made of many, varied pieces
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Figure 7.5
Glyco-protein
Carbohydrate
Glycolipid
Microfilamentsof cytoskeleton
EXTRACELLULARSIDE OFMEMBRANE
CYTOPLASMIC SIDEOF MEMBRANE
Integralprotein
Peripheralproteins
Cholesterol
Fibers of extra-cellular matrix (ECM)
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Figure 7.2
Hydrophilichead
Hydrophobictail
WATER
WATER
Membrane Composition – Phospholipid bilayer
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Figure 7.3
Phospholipidbilayer
Hydrophobic regionsof protein
Hydrophilicregions of protein
Membrane Composition▪ Membrane bound proteins have hydrophobic regions
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Membrane Composition - Fluidity▪ Phospholipids and some proteins can move
▪ Most drift laterally
▪ Sometimes (rarely) flip transversly
Figure 7.6
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Membrane Composition - Fluidity▪ Must be fluid to work properly
▪ Fluidity depends on temperature– Lower temperatures – less fluid
▪ Phospholipid types vary– Unsaturated fatty acids are more fluid than saturated
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▪ Cholesterol in animal cell membranes helps maintain fluidity– Steroid
– At warm temps (37 degrees) it slows movement of phospholipids
– As temp cools, it maintains fluidity by preventing tight packing
Membrane Composition – Fluidity & Cholesterol
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Membrane Composition – Fluidity
▪ Lipid composition varies from species to species– They are adapted to specific environments
– Some species have the ability to change composition in response to temperature changes where they live.
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Membrane Composition - Proteins
▪ Lots of different proteins– Embedded in the fluid matrix of the lipid bilayer
▪ Proteins determine most of the membrane’s specific function
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Membrane Composition - Proteins
▪ Peripheral proteins – bound to the surface of the membrane
▪ Integral proteins – penetrate the hydrophobic core– Transmembrane proteins – span the membrane
– Hydrophobic regions of the protein are usually alpha helices made of nonpolar amino acids
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Figure 7.9
N-terminus
helix
C-terminus
EXTRACELLULARSIDE
CYTOPLASMICSIDE
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Membrane Composition – Proteins
▪ Transport
▪ Enzymatic activity
▪ Signal transduction
▪ Cell-cell recognition
▪ Intercellular joining
▪ Attachment to the cytoskeleton and Extracellular matrix (ECM)
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Membrane Composition – Transport Proteins
Figure 7.10a
Enzymes
Signaling molecule
Receptor
Signal transductionATP
(a) Transport (b) Enzymatic activity(c) Signal transduction
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Selective Permeability
▪ Cell must exchange materials with it’s surroundings– Controlled by the plasma membrane
– Nutrients, signaling molecules, Ions in; waste products out.
▪ Selectively permeable – the membrane selects what goes in and out, only allowing specific things
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Selective PermiabilitySmall, nonpolar molecules can move through
Large, polar molecules can’t
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Selective Permeability – Transport Proteins
▪ Allow hydrophilic substances to cross the membrane
▪ Two types:– Channel proteins
▪ Have a hydrophilic channel that allows polar molecules through
▪ Aquaporins are specific for the movement of water
– Carrier Proteins▪ Bind to molecules and move them across
▪ Once the molecule binds, the carrier protein changes shape to move it across
▪ They are specific for the substances they move
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Selective Permeability – Transport Proteins; Channel proteins
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Selective Permeability – Transport Proteins; Channel proteins
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Selective Permeability – Passive transport; diffusion
▪ Diffusion – the tendency of molecules to spread out evenly into the available space
▪ Can be directional
▪ At dynamic equilibrium – equal number of molecules moving in both directions
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Figure 7.13a
Molecules of dyeMembrane (cross section)
WATER
(a) Diffusion of one solute
Net diffusion Net diffusion Equilibrium
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Figure 7.13b
(b) Diffusion of two solutes
Net diffusion Net diffusion
Net diffusion Net diffusion
Equilibrium
Equilibrium
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Selective Permeability – Passive transport; diffusion
▪ Substances move down their concentration gradient– No work is done
– Diffusion across a membrane, down the concentration gradient is called passive transport▪ No energy is expended
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Selective Permeability – Passive transport; Osmosis
▪ The diffusion of water across a selectively permeable membrane
▪ Water moves from low solute concentration to higher solute concentration– Diffuses until the solute concentration is equal on both sides of
the membrane
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Figure 7.14
Lowerconcentrationof solute (sugar)
Higher concentrationof solute
Sugarmolecule
H2O
Same concentrationof solute
Selectivelypermeablemembrane
Osmosis
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Selective Permeability – Passive transport; Osmosis
▪ Tonicity – the ability of a surrounding solution to cause a cell to gain or lose water
▪ Isotonic solution – Solute concentration is the same outside as it is inside the cell– No net movement of water across the membrane
▪ Hypertonic solution – solute concentration outside is greater than that inside the cell; cell loses water
▪ Hypotonic solution – solute concentration outside is less than that inside the cell; cell gains water
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Figure 7.15
Hypotonicsolution
Osmosis
Isotonicsolution
Hypertonicsolution
(a) Animal cell
(b) Plant cell
H2O H2O H2O H2O
H2O H2O H2O H2OCell wall
Lysed Normal Shriveled
Turgid (normal) Flaccid Plasmolyzed
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Selective Permeability – Passive transport; Osmosis
▪ Osmoregulation – organisms need mechanisms for controlling water loss or gain. – Various organisms manage osmosis differently based on
adaptations to their specific environments
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Selective Permeability – Passive transport; Facilitated diffusion▪ Facilitated diffusion – passive transport aided by
proteins– Transport proteins speed the passive movement of molecules
across the membrane
– Channel proteins▪ Aquaporins – faclilitated diffusion of water
▪ Ion channels – gates that open or close in response to a stimulus
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Selective Permeability – Active transport
▪ Moving solutes against their concentration gradient requires energy– Usually provided in the form of ATP
– Specific proteins are required for specific substances
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Figure 7.19Passive transport Active transport
Diffusion Facilitated diffusionATP
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Selective Permeability – Active transport; sodium potassium pump
▪ ECM – High Sodium, Low potassium
▪ Cytoplasm – Low Sodium, High potassium
▪ Potassium moves out – Sodium moves in
ECM Cytoplasm
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Figure 7.18-1
EXTRACELLULARFLUID
[Na] high[K] low
[Na] low[K] high
CYTOPLASM
Na
Na
Na
1
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Figure 7.18-2
EXTRACELLULARFLUID
[Na] high[K] low
[Na] low[K] high
CYTOPLASM
Na
Na
Na
1 2
Na
Na
Na
PATP
ADP
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Figure 7.18-3
EXTRACELLULARFLUID
[Na] high[K] low
[Na] low[K] high
CYTOPLASM
Na
Na
Na
1 2 3
Na
Na
Na
Na
Na
Na
P PATP
ADP
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Figure 7.18-4
EXTRACELLULARFLUID
[Na] high[K] low
[Na] low[K] high
CYTOPLASM
Na
Na
Na
1 2 3
4
Na
Na
Na
Na
Na
Na
K
K
P P
PP i
ATP
ADP
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Figure 7.18-5
EXTRACELLULARFLUID
[Na] high[K] low
[Na] low[K] high
CYTOPLASM
Na
Na
Na
1 2 3
45
Na
Na
Na
Na
Na
Na
K
K
K
K
P P
PP i
ATP
ADP
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Figure 7.18-6
EXTRACELLULARFLUID
[Na] high[K] low
[Na] low[K] high
CYTOPLASM
Na
Na
Na
1 2 3
456
Na
Na
Na
Na
Na
Na
K
K
K
K
K
K
P P
PP i
ATP
ADP
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Selective Permeability - Ion pumps
▪ Membrane potential – the voltage difference across a membrane– Positive and negative ions are separated on either side of a
membrane creating a voltage potential
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Selective Permeability - Ion pumps
▪ Electrochemical Gradient – drives the diffusion of ions across a membrane– Two forces make up the electrochemical gradient
▪ Chemical force – the ion’s concentration gradient
▪ Electrical force – the effect of the membrane potential on the ion’s movement
▪ Electrogenic Pump – a transport protein that generates voltage across a membrane– Sodium-potassium pump in animals
– Proton pump in plants
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Selective Permeability - Ion pumps; nerve impulse
▪ https://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html