Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition Solomon Berg Martin Chapter 5 Biological Membranes

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Biological membranes Complex, dynamic structures made of lipid and protein molecules Perform many functions –Define cell as a compartment –Regulate passage of materials –Participate in chemical reactions –Transmit signals between cell interior and the environment –Act as part of energy transfer and storage

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Biological membranes Physically separate cell interior from extracellular environment Form compartments within eukaryotic cells Plasma membrane –Regulates passage of materials –Participates in biochemical reactions –Receives information about environment –Communicates with other cells

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Phospholipids form bilayers in water Phospholipids in waterDetergent in water

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Fluid mosaic model Membranes consist of fluid phospholipid bilayer with a mosaic pattern of associated proteins Phospholipid molecules are amphipathic and contain –Hydrophobic regions –Hydrophilic regions

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Plasma membrane of mammalian red blood cell

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Membrane properties Orderly arrangement of phospholipid molecules make the cell membrane a liquid crystal –Allow molecules to move rapidly –Proteins move within membrane Lipid bilayers are –Flexible –Self-sealing –Can fuse with other membranes

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Detailed structure of the plasma membrane

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Integral membrane proteins Embedded in the bilayer Transmembrane proteins Integral proteins that extend completely through the membrane Peripheral member proteins Associated with the surface of the bilayer

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Membrane proteins, lipids, and carbohydrates Asymmetrically positioned to bilayer Sides have different composition and structure Function of member proteins –Transport of materials –Acting as enzymes or receptors –Cell recognition –Structurally linking cells

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Asymmetry of the plasma membrane

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Functions of membrane proteins

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Membranes are selectively permeable Physical processes –Osmosis –Diffusion Carrier-mediated processes –Channel proteins –Carrier proteins

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Diffusion: net movement of a substance from a region of greater to lower concentration

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Osmosis: water passes through selectively permeable membrane from region of higher concentration to lower

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Osmotic pressure Concentration of dissolved substances in a solution Isotonic: equal solute concentration Hypertonic: loses water in plasmolysis Hypotonic: gains water and swells Turgor pressure Internal hydrostatic pressure in walled cells

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Response of animal cells to osmotic pressure

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Turgor pressure and plasmolysis

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Facilitated diffusion Occurs down a concentration gradient Active transport Moves ions or molecules against a concentration gradient Cotransport ATP-powered pump maintains a concentration gradient

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Sodium-potassium pump

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Cells expend metabolic energy to carry on physiological processes Exocytosis Endocytosis –Phagocytosis –Pinocytosis –Receptor-mediated endocytosis

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Exocytosis

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Phagocytosis

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Pinocytosis

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Receptor-mediated endocytosis

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Cells communicate by cell signaling Signaling molecules include Neurotransmitters Hormones Regulatory molecules

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Cell signaling involves Synthesis and release of signaling molecule Transport to target cells Reception by target cells Signal transduction Response by the cell Termination of signal

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Signal transduction

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Cells in close contact often develop intercellular junctions Anchoring junctions –Desmosomes –Adhering junctions Tight junctions Gap junctions Plasmodesmata

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Desmosomes

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Tight junctions

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Gap junctions

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 5 Biological Membranes Plasmodesmata