Chapter 5: Cellular Membranes CHAPTER 5 Cellular Membranes.

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Chapter 5: Cellular Membranes CHAPTER 5 Cellular Membranes

Transcript of Chapter 5: Cellular Membranes CHAPTER 5 Cellular Membranes.

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Chapter 5: Cellular Membranes

CHAPTER 5Cellular Membranes

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Chapter 5: Cellular Membranes

Chapter 5: Cellular MembranesMembrane Composition and StructureMembrane Composition and Structure

Cell AdhesionCell Adhesion

Passive Processes of Membrane TransportPassive Processes of Membrane Transport

Active TransportActive Transport

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Chapter 5: Cellular Membranes

Chapter 5: Cellular MembranesEndocytosisEndocytosis and and ExocytosisExocytosis

Membranes Are Not Simply BarriersMembranes Are Not Simply Barriers

Membranes Are DynamicMembranes Are Dynamic

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Chapter 5: Cellular Membranes

Membrane Composition and Structure

• Biological membranes consist of lipids, Biological membranes consist of lipids, proteins, and carbohydrates. proteins, and carbohydrates.

• The fluid mosaic model describes a The fluid mosaic model describes a phospholipid bilayer in which phospholipid bilayer in which membrane proteins move laterally membrane proteins move laterally within the membrane. within the membrane.

Review Figures Review Figures 5.15.1, 5.2, 5.244

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Chapter 5: Cellular Membranes

5.1

Figure 5.1Figure 5.1

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Chapter 5: Cellular Membranes

5.2

Figure 5.2Figure 5.2

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Chapter 5: Cellular Membranes

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 5.177

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Chapter 5: Cellular Membranes

Membrane Composition and Structure

• The two surfaces of a membrane may The two surfaces of a membrane may have different properties due to have different properties due to different phospholipid different phospholipid compositions, compositions, exposed integral membrane proteins, exposed integral membrane proteins, and peripheral membrane proteins. and peripheral membrane proteins.

• Defined regions of a plasma Defined regions of a plasma membrane may have different membrane may have different membrane proteins. membrane proteins.

Review Figures 5.1, 5.2Review Figures 5.1, 5.288

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Chapter 5: Cellular Membranes

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 5.19

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Chapter 5: Cellular Membranes

Cell Adhesion

• In an organism or tissue, cells In an organism or tissue, cells recognize and bind to each other by recognize and bind to each other by means of membrane proteins means of membrane proteins protruding from the cell surface. protruding from the cell surface.

Review Figure 5.5Review Figure 5.510

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Chapter 5: Cellular Membranes

5.5

Figure 5.5Figure 5.5

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Chapter 5: Cellular Membranes

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 5.612

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Chapter 5: Cellular Membranes

5.6 – Part 1

Figure 5.6 – Part 1Figure 5.6 – Part 1

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Chapter 5: Cellular Membranes

5.6 – Part 2

Figure 5.6 – Part 2Figure 5.6 – Part 2

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Chapter 5: Cellular Membranes

Passive Processes of Membrane Transport

• Substances can diffuse passively Substances can diffuse passively across a membrane by: across a membrane by: • unaided diffusion through the unaided diffusion through the

phospholipid bilayer phospholipid bilayer • facilitated diffusion through facilitated diffusion through

protein channels protein channels • carrier proteins. carrier proteins.

Review Table 5.1Review Table 5.115

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Chapter 5: Cellular Membranes

Table 5.1

Table 5.1Table 5.1

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Chapter 5: Cellular Membranes

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 5.717

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Chapter 5: Cellular Membranes

5.7

Figure 5.7Figure 5.7

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Chapter 5: Cellular Membranes

Passive Processes of Membrane Transport

• The rate of simple diffusion of a solute The rate of simple diffusion of a solute across a membrane is directly across a membrane is directly proportional to the concentration proportional to the concentration gradient across the membrane. gradient across the membrane.

• A related important factor is the lipid A related important factor is the lipid solubility of the solute.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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Chapter 5: Cellular Membranes

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 5.821

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Chapter 5: Cellular Membranes

5.8

Figure 5.8Figure 5.8

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Chapter 5: Cellular Membranes

Passive Processes of Membrane Transport

• The cell walls of plants and some other The cell walls of plants and some other organisms prevent cells from bursting organisms prevent cells from bursting under hypotonic conditions. under hypotonic conditions.

• Turgor pressure develops under these Turgor pressure develops under these conditions and keeps plants upright conditions and keeps plants upright and stretches the cell wall during cell and stretches the cell wall during cell growth. growth.

Review Figure 5.8Review Figure 5.823

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Passive Processes of Membrane Transport

• Channel proteins and carrier proteins function in facilitated diffusion.

Review Figures 5.9, 5.1024

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Chapter 5: Cellular Membranes

5.9

Figure 5.9Figure 5.9

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Chapter 5: Cellular Membranes

5.10

Figure 5.10Figure 5.10

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Chapter 5: Cellular Membranes

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 Active transport requires energy to move substances across a membrane move substances across a membrane against a concentration gradient. against a concentration gradient.

Review Table Review Table 5.15.1

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Chapter 5: Cellular Membranes

Table 5.1

Table 5.1Table 5.1

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Active Transport

• Active transport proteins may be uniports, symports, or antiports.

Review Figure 5.1130

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Chapter 5: Cellular Membranes

5.11

Figure 5.11Figure 5.11

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Chapter 5: Cellular Membranes

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 2.32

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Chapter 5: Cellular Membranes

5.12

Figure 5.12Figure 5.12

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Chapter 5: Cellular Membranes

Active Transport

• Secondary active transport couples the Secondary active transport couples the passive movement of one solute with passive movement of one solute with its concentration gradient to the its concentration gradient to the movement of another solute against movement of another solute against its concentration gradient. its concentration gradient.

• Energy from ATP is used indirectly to Energy from ATP is used indirectly to establish the concentration gradient establish the concentration gradient resulting in movement of the first resulting in movement of the first solute. solute.

Review Figure 5.13Review Figure 5.13 34

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Chapter 5: Cellular Membranes

5.13

Figure 5.13Figure 5.13

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Chapter 5: Cellular Membranes

Endocytosis and Exocytosis

• Endocytosis transports Endocytosis transports macromolecules, large particles, and macromolecules, large particles, and small cells into eukaryotic cells by small cells into eukaryotic cells by means of engulfment and by vesicle means of engulfment and by vesicle formation from the plasma membrane. formation from the plasma membrane.

Review Figures 5.14Review Figures 5.143636

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Chapter 5: Cellular Membranes

5.14

Figure 5.14Figure 5.14

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Chapter 5: Cellular Membranes

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.39

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Membranes Are Not Simply Barriers

• Membranes function as sites for Membranes function as sites for recognition and initial processing of recognition and initial processing of extracellular signals, for energy extracellular signals, for energy transformations, and for organizing transformations, and for organizing chemical reactions. chemical reactions.

Review Figure 5.17Review Figure 5.174040

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5.17 – Part 1

Figure 5.17 – Part 1Figure 5.17 – Part 1

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5.17 – Part 2

Figure 5.17 – Part 2Figure 5.17 – Part 2

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Membranes Are Dynamic

• Although not all cellular membranes Although not all cellular membranes are identical, ordered modifications in are identical, ordered modifications in membrane composition accompany membrane composition accompany the conversions of one type of the conversions of one type of membrane into another type. membrane into another type.

Review Figure 5.18Review Figure 5.1843

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Chapter 5: Cellular Membranes

5.18

Figure 5.18Figure 5.18

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