Presentation on theme: "1-1 Inquiry into Life Eleventh Edition Sylvia S. Mader Chapter 4 Lecture Outline Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction."— Presentation transcript:
1-1 Inquiry into Life Eleventh Edition Sylvia S. Mader Chapter 4 Lecture Outline Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1-2 4.1 Plasma membrane structure and function Membrane structure –Fluid-mosaic model –Phospholipid bilayer Hydrophobic tails face inward Hydrophilic heads face surfaces –Proteins Integral proteins-embedded Peripheral proteins- surface –Glycoproteins, glycolipids, cholesterol
1-3 The plasma membrane separates the internal environment of the cell from its surroundings. The plasma membrane is a phospholipid bilayer with embedded proteins. The plasma membrane has a fluid consistency and a mosaic pattern of embedded proteins.
1-4 Fluid-mosaic model of membrane structure Fig. 4.1
1-5 Membrane structure and function, cont’d. Functions of membrane proteins –Channel proteins Form channels for substances can move across membrane –Receptor proteins Bind to substances in the environment and trigger cell responses –Carrier proteins Transport specific substances across cell membrane –Enzymes Catalyze chemical reactions for cell metabolism
1-12 Membrane structure and function, cont’d. Carbohydrate chains –Bound to only outer surface of cell recognition proteins –Form a “sugar coat”-glycocalyx –Diversity of this Glycocalyx produces individual “fingerprint” Recognition of self vs. nonself Immune responses Glycocalyx is only on the outer surfaces, so the inner and outer surfaces of the Cell Membrane are not identical.
1-13 In animal cells, the carbohydrate chains of cell recognition proteins are collectively called the glycocalyx. The glycocalyx can function in cell-to-cell recognition, adhesion between cells, and reception of signal molecules. The diversity of carbohydrate chains is enormous, providing each individual with a unique cellular “fingerprint”.
1-14 4.2 Permeability of plasma membrane Plasma membrane is referred to as selectively permeable or differentially permeable –Some substances pass through freely while others do not. Small, uncharged molecules pass through the cell membrane, following their concentration gradient. Passive transport-no cellular energy required –Kinetic energy drives passive mechanisms –Movement is always from high concentration to low –Diffusion, facilitated diffusion (carrier-mediated)
1-15 The plasma membrane is differentially permeable. Macromolecules cannot pass through because of size, and tiny charged molecules do not pass through the nonpolar interior of the membrane. Small, uncharged molecules pass through the membrane, following their concentration gradient.
1-16 Passage of molecules into and out of cells Table 4.1
1-17 Permeability of plasma membrane, cont’d. Active transport mechanisms-require ATP, can transport against a concentration gradient –Active transport Requires a carrier protein Transports molecules from low concentration to high –Exocytosis-vesicle mediated transport – Uses Energy Transports cell products and wastes out of the cell by vesicle formation. The release of digestive enzymes from cells of the pancreas, or secretion of the hormone insulin in response to rising blood glucose levels are examples. –Endocytosis-vesicle mediated transport–Uses Energy Transports substances into the cell by vesicle formation Pinocytosis-”cell drinking”, takes in small particles or liquids Phagocytosis-”cell eating”, takes in larger particles
1-18 Movement of materials across a membrane may be passive or active. Passive transport does not use chemical energy; diffusion and facilitated transport are both passive. Active transport requires chemical energy and usually a carrier protein. Exocytosis and endocytosis transport macromolecules across plasma membranes using vesicle formation, which requires energy.
1-20 4.3 Diffusion and osmosis Diffusion –Movement of molecules from an area of high concentration to an area of low concentration –Random kinetic energy drives diffusion –Lipid soluble molecules, gases, and some small water soluble molecules may diffuse freely across cell membrane
1-22 A solution contains a solute (solid) and a solvent (liquid). Cells are normally isotonic to their surroundings, and the solute concentration is the same inside and out of the cell. “Iso” means the same as, and “tonocity” refers to the strength of the solution. Osmosis in cells
1-23 4.3 Diffusion and osmosis, cont’d. Osmosis-diffusion of water across a semi permeable membrane –Osmotic pressure-force that causes water to move in a direction –Osmotic pressure is due to the number of nondiffusable particles in solution –Hypotonic solutions-cause cells to swell and burst, called lysis in animal cells, increased turgor pressure in plant cells since cell walls resist rupture. –Hypertonic solutions-cause cells to shrink, called crenation in animal cells, plasmolysis in plant cells. –Isotonic solutions-no change
1-26 4.4 Transport by carrier proteins Transport by carrier proteins –Carrier proteins are specific for the molecules they transport Facilitated transport –Passive mechanism –Transports from high concentration to low Active transport –Requires cellular energy –Transports against the concentration gradient –The sodium-potassium pump moves sodium ions to the outside of the cell and potassium ions to the inside.
1-27 Facilitated transport and active transport Fig. 4.8Fig. 4.9
1-31 Exocytosis and endocytosis, cont’d. Endocytosis-an area of cell membrane invaginates and surrounds a substance, then pinches off to form a vesicle –Phagocytosis-material taken in is large; ex: bacteria, cell debris –Pinocytosis-material is liquid or small –Receptor-mediated-specific type of pinocytosis which occurs in response to receptor stimulation, often with a coated pit, an area with a high concentration of receptors