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Mader: Biology 8th Ed.
Membrane Structure and Function
Chapter 5
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Mader: Biology 8th Ed.
Outline
• Membrane Models– Fluid-Mosaic
• Plasma Membrane Structure and Function– Protein Functions– Plasma Membrane Permeability
DiffusionOsmosisTransport Via Carrier Proteins
• Cell Surface Modifications
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Mader: Biology 8th Ed.
Membrane Models
• Fluid-Mosaic Model– Membrane is a fluid phospholipid bilayer
in which protein molecules are either partially or wholly embedded.
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Mader: Biology 8th Ed.
Fluid-Mosaic Model
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Mader: Biology 8th Ed.
Plasma Membrane Structure and Function
• Plasma membrane separates internal environment from the external environment.
• Hydrophilic polar heads face outside, and hydrophobic nonpolar tails face each other.
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Mader: Biology 8th Ed.
Plasma Membrane Structure and Function
• Proteins may be peripheral or integral.– Peripheral proteins are found on the inner
membrane surface.– Integral proteins are embedded in the
membrane.
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Mader: Biology 8th Ed.
Protein Functions
• Channel Proteins - Involved in passage of molecules through membrane.
• Carrier Proteins - Combine with substance to aid in passage through membrane.
• Cell Recognition Proteins - Help body recognize foreign substances.
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Mader: Biology 8th Ed.
Protein Functions
• Receptor Proteins - Allow molecule binding, causing protein to change shape and bring about cellular change.
• Enzymatic Proteins - Carry out metabolic reactions directly.
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Mader: Biology 8th Ed.
Plasma Membrane Permeability
• Plasma membrane is differentially permeable. – Passive Transport - No ATP requirement.
Molecules follow concentration gradient.
– Active Transport - Requires carrier protein and ATP.
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Mader: Biology 8th Ed.
Crossing Plasma Membrane
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Mader: Biology 8th Ed.
Diffusion
• Diffusion - Movement of molecules from a higher to a lower concentration until equilibrium is reached.– Down concentration gradient
• A solution contains a solute (solid) and a solvent (liquid).
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Mader: Biology 8th Ed.
Diffusion
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Mader: Biology 8th Ed.
Osmosis
• Osmosis - Diffusion of water across a differentially (selectively) permeable membrane due to concentration differences.– Osmotic pressure is the pressure that
develops due to osmosis.The greater the osmotic pressure, the
more likely water will diffuse in that direction.
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Mader: Biology 8th Ed.
Osmosis
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Mader: Biology 8th Ed.
Osmosis
• Isotonic Solution - Solute and water concentrations both inside and outside the membrane are equal.
• Hypotonic Solution - Solution with a lower concentration of solute than the solution on the other side of the membrane.– Cells placed in a hypotonic solution will
swell.Lysis
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Mader: Biology 8th Ed.
Osmosis
• Hypertonic Solution - Solution with a higher concentration of solute than the solution on the other side of the membrane.– Cells placed in a hypertonic solution will
shrink.Plasmolysis
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Mader: Biology 8th Ed.
Transport by Carrier Proteins• Carrier proteins combine with a certain
molecules which are then transported through the membrane.– Facilitated Transport
Small molecules follow concentration gradient by combining with carrier proteins.
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Mader: Biology 8th Ed.
Transport by Carrier Proteins
– Active TransportSmall molecules move against their
concentration gradient by combining with carrier proteins.
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Mader: Biology 8th Ed.
Membrane-Assisted Transport
• Large marcomolecules are transported into or out of the cell by vesicle formation.– Exocytosis - Vesicles fuse with plasma
membrane as secretion occurs.
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Mader: Biology 8th Ed.
Membrane-Assisted Transport
– Endocytosis - Cells take in substances by vesicle formation.
Phagocytosis - Large, solid material.Pinocytosis - Liquid or small, solid
particles.Receptor-Mediated - Specific form of
pinocytosis using a coated pit.
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Mader: Biology 8th Ed.
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Mader: Biology 8th Ed.
Cell Surface Modifications
• Cell Surfaces in Animals– Junctions Between Cells
Adhesion Junctions Intercellular filaments between cells.
Tight Junctions Form impermeable barriers.
Gap Junctions Plasma membrane channels are
joined (allows communication).
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Mader: Biology 8th Ed.
Cell Surface Modifications
– Extracellular MatrixMeshwork of polysaccharides and
proteins in close association with the cell that produced them.
• Plant Cell Walls– Plants have freely permeable cell wall, with
cellulose as the main component.Joined by plasmodesmata that spans cell
wall and contains strands of cytoplasm that allow passage of material between cells.
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Mader: Biology 8th Ed.
Review
• Membrane Models– Fluid-Mosaic
• Plasma Membrane Structure and Function– Protein Functions– Plasma Membrane Permeability
DiffusionOsmosisTransport Via Carrier Proteins
• Cell Surface Modifications
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Mader: Biology 8th Ed.