Biological Membranes Chapter 5 PDF

Biological Membranes Chapter 5  Plasma Membrane 1. Physically separates interior of cell from external environment 2. Receives information about changes in environment 3. Regulates passage of materials in and out of cell  Plasma Membrane 4. Communica...

Biological Membranes Chapter 5  Plasma Membrane 1. Physically separates interior of cell from external environment 2. Receives information about changes in environment 3. Regulates passage of materials in and out of cell  Plasma Membrane 4. Communicates with other cells 5. Forms compartments to allow separate functions 6. Participates in biochemical reactions  Hydrophilic Hydrophobic region of protein region of protein Phospholipid bilayer Peripheral Integral protein (transmembrane) protein (b) Fluid mosaic model. According to this model, a cell membrane is a fluid lipid bilayer with a constantly changing “mosaic pattern“ of associated proteins. Fig. 5-2b, p. 108  Phospholipid Molecules Amphipathic: both hydrophobic and hydrophilic regions hydrophilic heads at 2 surfaces of bilayer hydrophobic fatty acid chains interior  The Lipid Bilayer Lipids of the bilayer fluid or liquid-crystalline state Proteins move within the membrane  Lipid Bilayer Flexible and self-sealing Fuses with other membranes allows transport of materials within cell Forms vesicles bud from one cell membrane fuse with another membrane  Carbohydrate chains Glycoprotein Carbohydrate Extracellular Hydrophobic chain fluid Hydrophilic Glycolipid Cholesterol Hydrophilic α-helix Integral Peripheral proteins protein Cytosol Fig. 5-6, p. 111  Membrane Proteins Integral membrane proteins embedded in bilayer Transmembrane proteins extend completely through membrane Peripheral membrane proteins at surface of bilayer bound to exposed integral proteins Membrane Proteins Membrane Protein Synthesis  Membrane Proteins Transport materials Act as enzymes or receptors Recognize cells Structurally link cells Functions of Membrane Proteins Functions of Membrane Proteins  Selectively Permeable Membranes Allow passage of some substances but not others Controls volume and internal composition of cell’s ions and molecules  Transport Proteins 1. Membrane transport proteins facilitate certain ions and molecules through biological membranes 2. Carrier proteins transport proteins that change as they bind and transport a specific solute 3. ABC transporters carrier proteins that use energy from ATP to transport solutes  Transport Proteins 4. Channel proteins allow water and certain ions through the membrane 5. Porins channel proteins with large pores allow water and certain solutes through membrane  Diffusion Net movement of substance down its concentration gradient from region of greater concentration to region of lower concentration Does not use direct metabolic energy Diffusion  Simple vs Facilitated Simple diffusion molecules or ions move directly through the membrane down their concentration gradient Facilitated diffusion specific transport proteins move solutes across a membrane down their concentration gradient Facilitated Diffusion  Osmosis A type of diffusion H2O molecules pass through a selectively permeable membrane from higher effective H2O concentration to lower effective H2O concentration Osmosis  Osmotic Pressure Determined by concentration of solutes Cells regulate internal osmotic pressure to prevent shrinking or bursting  Tonicity Isotonic solutions equal solute concentration Hypertonic solution in solute concentration > the cell’s cell loses water to surroundings Hypotonic solution in solute concentration < the cell’s water enters, cells swell Osmotic Pressure  Plant Cells Plasmolysis in hypertonic solution, water moves out plasma membrane splits from cell wall Turgor pressure in hypotonic solution, water moves in cells swell, build pressure against cell walls Turgor and Plasmolysis  Active Transport  Cell uses metabolic energy to move ions or molecules across a membrane against a concentration gradient Example: sodium–potassium pump uses ATP to pump sodium ions out and potassium ions in Sodium-Potassium Pump  Indirect Active Transport Carrier protein cotransports 2 solutes 1 solute down its concentration gradient 1 solute against its concentration gradient ATP-powered pump maintains concentration gradient Cotransport  Exocytosis Materials exit cell Membrane surface area increases 1 Vesicle approaches plasma membrane, 2 fuses with it, and 0.25 μm 3 releases its contents outside cell. Fig. 5-20, p. 124  Endocytosis Materials enter cell Membrane surface area decreases 3 types of endocytosis phagocytosis pinocytosis receptor-mediated endocytosis  Phagocytosis Large particles enter cell  Vacuole Lysosomes Lysosome Lysosome 1 Folds of plasma membrane 2 Vacuole then pinches off 3 Lysosomes fuse with surround particle to be ingested, inside cell. vacuole and pour potent forming small vacuole around it. hydrolytic enzymes onto ingested material. Ingested bacteria Nucleus Glycogen (stored nutrients) Bacteria Large Lysosomes vacuole Fig. 5-21, p. 125  Pinocytosis Dissolved materials enter cell