Life, 6th Edition

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CHAPTER 5Cellular Membranes
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Chapter 5 Cellular Membranes

• Membrane Composition and Structure
• Cell Adhesion
• Passive Processes of Membrane Transport
• Active Transport

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Chapter 5 Cellular Membranes

• Endocytosis and Exocytosis
• Membranes Are Not Simply Barriers
• Membranes Are Dynamic

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Membrane Composition and Structure

• Biological membranes consist of lipids, proteins,
  and carbohydrates.
• The fluid mosaic model describes a phospholipid
  bilayer in which membrane proteins move laterally
  within the membrane.
• Review Figures 5.1, 5.2
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5.1
figure 05-01.jpg

• Figure 5.1

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5.2
figure 05-02.jpg

• Figure 5.2

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Membrane Composition and Structure

• Integral membrane proteins are partially inserted
  into the phospholipid bilayer.
• Peripheral proteins attach to its surface by
  ionic bonds.
• Review Figure 5.1
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Membrane Composition and Structure

• The two surfaces of a membrane may have different
  properties due to different phospholipid
  compositions, exposed integral membrane proteins,
  and peripheral membrane proteins.
• Defined regions of a plasma membrane may have
  different membrane proteins.
• Review Figures 5.1, 5.2
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Membrane Composition and Structure

• Carbohydrates attached to proteins or
  phospholipids project from the external surface
  of the plasma membrane and function as
  recognition signals between cells.
• Review Figure 5.1
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Cell Adhesion

• In an organism or tissue, cells recognize and
  bind to each other by means of membrane proteins
  protruding from the cell surface.
• Review Figure 5.5
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5.5
figure 05-05.jpg

• Figure 5.5

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Cell Adhesion

• Tight junctions prevent passage of molecules
  through space around cells, and define functional
  regions of the plasma membrane by restricting
  migration of membrane proteins over the cell
  surface.
• Desmosomes allow cells to adhere strongly to one
  another.
• Gap junctions provide channels for chemical and
  electrical communication between cells.
• Review Figure 5.6
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5.6 Part 1
figure 05-06a.jpg

• Figure 5.6 Part 1

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5.6 Part 2
figure 05-06b.jpg

• Figure 5.6 Part 2

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Passive Processes of Membrane Transport

• Substances can diffuse passively across a
  membrane by
• unaided diffusion through the phospholipid
  bilayer
• facilitated diffusion through protein channels
• carrier proteins.
• Review Table 5.1
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Table 5.1
table 05-01.jpg

• Table 5.1

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Passive Processes of Membrane Transport

• Solutes diffuse across a membrane from a region
  with a greater solute concentration to a region
  of lesser.
• Equilibrium is reached when the concentrations
  are identical on both sides.
• Review Figure 5.7
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5.7
figure 05-07.jpg

• Figure 5.7

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Passive Processes of Membrane Transport

• The rate of simple diffusion of a solute across a
  membrane is directly proportional to the
  concentration gradient across the membrane.
• A related important factor is the lipid
  solubility of the solute.
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Passive Processes of Membrane Transport

• In osmosis, water diffuses from regions of higher
  water concentration to regions of lower
  concentration across a membrane.
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Passive Processes of Membrane Transport

• In hypotonic solutions, cells tend to take up
  water while in hypertonic solutions, they tend to
  lose it.
• Animal cells must remain isotonic to the
  environment to prevent destructive loss or gain
  of water.
• Review Figure 5.8
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5.8
figure 05-08.jpg

• Figure 5.8

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Passive Processes of Membrane Transport

• The cell walls of plants and some other organisms
  prevent cells from bursting under hypotonic
  conditions.
• Turgor pressure develops under these conditions
  and keeps plants upright and stretches the cell
  wall during cell growth.
• Review Figure 5.8
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Passive Processes of Membrane Transport

• Channel proteins and carrier proteins function in
  facilitated diffusion.
• Review Figures 5.9, 5.10
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5.9
figure 05-09.jpg

• Figure 5.9

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5.10
figure 05-10.jpg

• Figure 5.10

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Passive Processes of Membrane Transport

• The rate of carrier-mediated facilitated
  diffusion is at maximum when solute concentration
  saturates the carrier proteins so that no rate
  increase is observed with further solute
  concentration increase.
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Active Transport

• Active transport requires energy to move
  substances across a membrane against a
  concentration gradient.
• Review Table 5.1
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Table 5.1
table 05-01.jpg

• Table 5.1

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Active Transport

• Active transport proteins may be uniports,
  symports, or antiports.
• Review Figure 5.11
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5.11
figure 05-11.jpg

• Figure 5.11

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Active Transport

• In primary active transport, energy from the
  hydrolysis of ATP is used to move ions into or
  out of cells against their concentration
  gradients.
• Review Figure 5.12 Table 2.
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5.12
figure 05-12.jpg

• Figure 5.12

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Active Transport

• Secondary active transport couples the passive
  movement of one solute with its concentration
  gradient to the movement of another solute
  against its concentration gradient.
• Energy from ATP is used indirectly to establish
  the concentration gradient resulting in movement
  of the first solute.
• Review Figure 5.13
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5.13
figure 05-13.jpg

• Figure 5.13

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Endocytosis and Exocytosis

• Endocytosis transports macromolecules, large
  particles, and small cells into eukaryotic cells
  by means of engulfment and by vesicle formation
  from the plasma membrane.
• Review Figures 5.14
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5.14
figure 05-14.jpg

• Figure 5.14

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Endocytosis and Exocytosis

• In receptor-mediated endocytosis, a specific
  membrane receptor binds to a particular
  macromolecule.
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Endocytosis and Exocytosis

• In exocytosis, materials in vesicles are secreted
  from the cell when the vesicles fuse with the
  plasma membrane.
• Review Figure 5.14 again.
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Membranes Are Not Simply Barriers

• Membranes function as sites for recognition and
  initial processing of extracellular signals, for
  energy transformations, and for organizing
  chemical reactions.
• Review Figure 5.17
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5.17 Part 1
figure 05-17a.jpg

• Figure 5.17 Part 1

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5.17 Part 2
figure 05-17b.jpg

• Figure 5.17 Part 2

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Membranes Are Dynamic

• Although not all cellular membranes are
  identical, ordered modifications in membrane
  composition accompany the conversions of one type
  of membrane into another type.
• Review Figure 5.18
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5.18
figure 05-18.jpg

• Figure 5.18