Membrane Structure and Function Chapter 7

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Membrane Structure and FunctionChapter 7
Professor Pamela L. Pannozzo Principles of
Biology I BSC 1010
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Phospholipid Bilayer
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Plasma Membrane
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Membrane Fluidity
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Proteins Within the Membrane

• About 2 of the molecules found in plasma
  membrane
• 50 of its weight since they are large
• Float within the lipid bilayer, may be fixed
• Different proteins for different cells
• General Types
• Integral proteins pass through the membrane
• Peripheral proteins adhere to
• membrane surface

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Membrane Proteins Do a Lot
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Membrane Protein Functions (cont)
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Membrane Carbohydrates
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Extracellular Matrix

• Tissue strength
• Attach cells
• Cell signaling
• Activate gene expression
• Structural polysaccharides (create gelresist
  compression)
• Proteoglycans
• Glycosaminoglycans
• Chitin

• Structural proteins (bone, cartilage, connective
  tissue)
• Collagen, elastin
• Adhesive proteins (connect cells)
• fibronectin

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Membrane Sidedness
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Membrane Transport Movement Through the Cell
Membrane
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Plasma Membrane

• Regulates transport of molecules across cell
  boundaries
• Cell functions as an open system

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Selective Permeability

• Cell functions as open system
• Types of molecules
• Small hydrophobic molecules--hydrocarbons, CO2,
  O2
• Small hydrophilic molecules--water, ions, polar
  molecules
• Large molecules proteins, polysaccharides

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Diffusion

• Movement of solutes in solution across a membrane
• Movement from an area of higher concentration to
  lower concentration
• Concentration gradient
• Difference between two sides of a membrane
• Passive transport
• Requires no energy

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Diffusion
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Diffusion (cont)
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Osmosis

• Movement of water molecules across a membrane
• Special case of Diffusion
• Passive transport
• Direction of movement determined by total solute
  concentration on either side of the membrane
• Isotonic solutions with equal solute
  concentrations
• Hypertonic greater solute concentration
• Hypotonic lower solute concentration
• Cell shrinkage (crenation) or swelling (lysis)

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Osmosis
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Osmosis (cont)
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Facilitated Diffusion

• Movement of hydrophilic molecules across a
  membrane with the help of transport proteins
• Passive transport
• Movement from higher to lower concentration

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Active Transport

• Movement of molecules across a cell membrane
  against their concentration gradient
• Mechanisms
• Ion pumps
• Coupled transport
• Transport proteins act as pumps
• Conformational shape change
• Requires energy
• ATP phosphorylates transport protein
• Dephosphorylation restores original conformation

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Ion Pumps
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Coupled Transport
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Endocytosis

• Bulk (active) tranport, requires energy
• Movement of large molecules into a membrane by
  formation of a vesicle
• Types
• Phagocytosis
• Pinocytosis
• Receptor-mediated endocytosis

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Phagocytosis
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Pinocytosis and Receptor-Mediated Endocytosis
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Receptor Mediated Endocytosis EM
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Exocytosis

• Movement of large molecules out of a membrane
  through formation of a vesicle
• Examples
• Secretion of insulin by pancreas
• Secretion of mucus by salivary glands
• Secretion of chemical signals by nerve cells