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Cell Membranes: Osmosis and Diffusion

Cell Membranes: Osmosis and Diffusion. Membrane Functions . 1. Protect cell 2. Guard incoming and outgoing substances 3. Maintain ion concentrations of various substances Selectively permeable Allows some molecules in Others are kept out. Phospholipid Bilayer. Fluid Mosaic Model.

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Cell Membranes: Osmosis and Diffusion

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  1. Cell Membranes:Osmosis and Diffusion

  2. Membrane Functions 1. Protect cell 2. Guard incoming and outgoing substances 3. Maintain ion concentrations of various substances • Selectively permeable • Allows some molecules in • Others are kept out

  3. Phospholipid Bilayer

  4. Fluid Mosaic Model

  5. Solutions • Solutions are made of solute and a solvent • Solvent - the liquid into which the solute is poured and dissolved • Solute - substance that is dissolved or put into the solvent. Salt and sucrose are solutes

  6. Membrane Transport • Diffusion • Passive transport • No energy expended • Osmosis • Passive transport • Water across membrane

  7. Diffusion • Movement of molecules from one side of a membrane to the other • Occurs from a region of high concentration of substance to a region of lower concentration

  8. Di f fus ion

  9. Osmosis

  10. Membrane Transport • Facilitated Diffusion • Passive transport • Use of proteins to carry polar molecules or ions across • Active Transport • Requires energy to transport molecules against a concentration gradient • Energy is in the form of ATP

  11. Tonicity • Hypotonic Solution • Inside has higher salt concentration • Hypertonic Solution • Inside has lower salt concentration • Isotonic Solution • Both solutions have same concentrations of solute

  12. Plant and Animal Cells in Various Solutions

  13. Active Transport • Movement against a concentration gradient (from low to high concentration) • Requires added energy (ATP) and a specific membrane carrier (“pump”)

  14. Endocytosis • Ingestion of large molecules or particles • Cell surrounds and envelops substance forming a vesicle which fuses with lysosome • Phagocytosis • Endocytosis of organism • Pinocytosis • Endocytosis of large, soluble molecules

  15. Exocytosis • Cell secretes material • Package in a vesicle • Moves in vesicle to cell surface • Vesicle membrane fuses with cell membrane • Contents are secreted out • Specialized animal cells produce and secrete digestive enzymes and hormones

  16. Cell Structure and Function

  17. Early Discoveries • Mid 1600s - Robert Hooke observed and described cells in cork • Late 1600s - Antony van Leeuwenhoek observed sperm, microorganisms • 1820s - Robert Brown observed and named nucleus in plant cells

  18. Cell Theory • Matthias Schleiden • Theodor Schwann • Rudolf Virchow

  19. Cell Theory 1) Every organism is composed of one or more cells 2) Cell is smallest unit having properties of life 3) Continuity of life arises from growth and division of single cells

  20. Cell • Smallest unit of life • Can survive on its own or has potential to do so • Is highly organized for metabolism • Senses and responds to environment • Has potential to reproduce

  21. Cells are Microscopic • Why aren’t cells larger? • Animal cells range from 7-50 μm, some are much larger: • Nerve cells • Algae • Eggs • Plant cells are generally larger

  22. Why aren’t Cells Larger? • As cells grow larger, volume increases faster than surface area • Large cells do not have sufficient surface area for efficient diffusion of nutrients and wastes • Nuclei control activities of smaller cells more easily

  23. Structure of Cells Must Have: • Plasma membrane • DNA Region • Cytoplasm Two types: • Prokaryotic • Eukaryotic

  24. Structure of Cells The plasma membrane and internal cell membranes consist of lipids and proteins. The lipids are organized as two adjacent layers—as bi-layer.

  25. Lipid Bilayer • Main component of cell membranes • Gives the membrane its fluid properties • Two layers of phospholipids

  26. Fluid Mosaic Model • Membrane is a mosaic of • Phospholipids • Glycolipids • Sterols • Proteins • Most phospholipids and some proteins can drift through membrane

  27. Membrane Proteins • Transport proteins • Receptor proteins • Recognition proteins • Adhesion proteins

  28. Why Are Cells So Small? • Surface-to-volume ratio • The bigger a cell is, the less surface area there is per unit volume • Above a certain size, material cannot be moved in or out of cell fast enough

  29. Microscopes • Create detailed images of something that is otherwise too small to see • Light microscopes • Simple or compound • Electron microscopes • Transmission EM or Scanning EM

  30. Light Microscope Limitations • Wavelengths of light are 400-750 nm (nanometers) • If a structure is less than one-half of a wavelength long, it will not be visible • Light microscopes can resolve objects down to about 200 nm in size

  31. Electron Microscopy • Uses streams of accelerated electrons rather than light • Electrons are focused by magnets rather than glass lenses • Can resolve structures down to 0.5 nm

  32. Eukaryotic Cells Plant cell • Defined as a cell that starts out life with a nucleus • Have a nucleus and other organelles • Eukaryotic organisms • Plants • Animals • Protista • Fungi Animal cell

  33. Animal Cell Features • Plasma membrane • Cytoskeleton • Nucleus • Ribosomes • Endoplasmic reticulum • Vesicle • Mitochondria • Golgi body

  34. Cell wall Chloroplast Central Vacuole Plant Cell Features • Nucleus • Plasma Membrane • Ribosomes • Endoplasmic reticulum • Golgi body • Mitochondria

  35. Functions of Nucleus • Keeps the DNA molecules of eukaryotic cells separated from metabolic machinery of cytoplasm • Makes it easier to organize DNA and to copy it before parent cells divide into daughter cells

  36. Components of Nucleus • Nuclear envelope - double membrane enclosing the nucleus • Nucleoplasm - fluid portion of the nucleus • Nucleolus - where other organelles are constructed • Chromosome – made of chromatin • Chromatin - DNA with all associated protein

  37. Nuclear Envelope • Two outer membranes (lipid bi-layers) • Innermost surface has DNA attachment sites • Pores span bi-layer

  38. Nucleolus • Dense mass of material in nucleus • May be one or more • Cluster of DNA and proteins • Puts together ribosomal subunits

  39. Chromatin • Cell’s collection of DNA and associated proteins • Chromosome is one DNA molecule and its associated proteins • Appearance changes as cell divides

  40. Cytomembrane System • Group of related organelles in which lipids are assembled and new polypeptide chains are modified • Products are sorted and shipped to various destinations

  41. Cyto-membrane System Endoplasmic reticulum Golgi bodies Vesicles

  42. Endoplasmic Reticulum • In animal cells, continuous with nuclear membrane • Extends throughout cytoplasm • Two regions - rough and smooth

  43. Rough ER • Arranged into flattened sacs • Ribosomes on surface give it a rough appearance • Some polypeptide chains enter rough ER and are modified • Cells that specialize in secreting proteins have lots of rough ER

  44. Smooth ER • A series of interconnected tubules • No ribosomes on surface • Lipids assembled inside tubules • Smooth ER of liver inactivates wastes, drugs

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