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Cellular Permeability and Transport Mechanisms

Explore the selective permeability of cells and tissues, passive and active transport processes, osmosis, and the role of diffusion in cellular physiology. Understand how cells regulate the movement of substances through the plasma membrane.

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Cellular Permeability and Transport Mechanisms

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  1. Cells and Tissues

  2. Selective Permeability • The plasma membrane allows some materials to pass while excluding others • This permeability includes movement into and out of the cell

  3. Cellular Physiology: Membrane Transport • Membrane Transport – movement of substances into and out of the cell • Transport is by two basic methods • Passive transport • No energy is required • Active transport • The cell must provide metabolic energy

  4. Movement Through Cell Membrane • Passive Mechanisms of transport require no cellular energy • Ex: • Simple Diffusion • Facilitated Diffusion • Osmosis • Filtration

  5. Passive Transport Processes • Diffusion • Molecules move from high concentration to low concentration, or down a concentration gradient • Equilibrium- Molecules tend to distribute themselves evenly within a solution PRESS TO PLAY DIFFUSION ANIMATION Figure 3.9

  6. Diffusion through the Plasma Membrane Figure 3.10

  7. Passive Transport Processes • Facilitated diffusion • Substances require a protein carrier (or Carrier Molecule) for passive transport • The rate of facilitated diffusion is limited to the number of carrier molecules in the membrane and/or the number of molecules available for transport. • Insulin promotes facilitated diffusion of glucose

  8. Facilitated Diffusion • diffusion across a membrane with the help of a channel or carrier molecule • glucose and • amino acids

  9. Passive Transport Processes • Osmosis – • simple diffusion of water from area of higher concentration to lower concentration • Osmotic Pressure- the amount of pressure (on surface of liquid) needed to stop osmosis

  10. Osmosis • movement of water through a selectively permeable membrane from region of higher concentration to region of lower concentration • water moves toward a higher concentration of solutes

  11. Osmosis Osmotic Pressure – ability of osmosis to generate enough pressure to move a volume of water Osmotic pressure increases as the concentration of nonpermeable solutes increases • hypertonic – higher osmotic pressure • hypotonic – lower osmotic pressure • isotonic – same osmotic pressure

  12. Passive Transport • These are red blood cells in three different solutions:

  13. Passive Transport • Hypertonic Solution • Has more solute particles (thus less H2O) than a cell in that solution • Result: Plasmolysis- cell shrinks

  14. Passive Transport • Hypotonic Solution • Has less solute particles (thus more H2O) than a cell in that solution • Result: Cytolysis- cell bursts

  15. Passive Transport • Isotonic Solution • Has the same concentration of solute particles as a cell in that solution • Result: Cell remains unchanged

  16. Passive Transport • Can you identify the solution each cell is in and explain what happens to each cell?

  17. Passive Transport Processes • Filtration • Water and solutes are forced through a membrane by fluid, or hydrostatic pressure • Ex: Blood pressure forces small molecules & water out through capillary walls creating tissue fluid while larger protein molecules remain inside capillary.

  18. Filtration • smaller molecules are forced through porous membranes • hydrostatic pressure important in the body • molecules leaving blood capillaries

  19. Active Transport Processes • Transport substances that are unable to pass by diffusion • They may be too large • They may not be soluble in the fat core of the membrane • They may have to move against a concentration gradient • Two common forms of active transport • Solute pumping – Active Transport • Bulk transport – Endocytosis, Exocytosis

  20. Active Transport Processes Active Mechanisms require cellular energy (ATP) Active Transport- Particles move from an area of lower concentration to higher concentration Up to 40% of cell’s energy supply is used for active transport

  21. Active Transport Processes • Solute pumping • Amino acids, some sugars and ions are transported by solute pumps • ATP energizes protein carriers, and in most cases, moves substances against concentration gradients PRESS TO PLAY ACTIVE TRANSPORT ANIMATION

  22. Active Transport Processes Figure 3.11

  23. Active Transport Processes • Bulk transport • Endocytosis • A portion of the cell membrane forms vesicle to carry in particles too large for diffusion or pumping

  24. Endocytosis Figure 3.13a

  25. Active Transport Processes • Types of endocytosis • Pinocytosis – cell drinking: • Portion of cell membrane becomes indented and surrounds tiny droplets of liquid. Membrane pinches off and carries liquid into cytoplasm where it releases contents • Phagocytosis – cell eating: • Solids are engulfed by indented portion of cell membrane which then pinches off and acts as vesicle to carry & empty solids into cytoplasm

  26. Active Transport Processes • Bulk transport • Exocytosis • Moves materials out of the cell • Material is carried in a membranous vesicle • Vesicle migrates to plasma membrane • Vesicle combines with plasma membrane • Material is released to the outside

  27. Exocytosis Figure 3.12a

  28. Cell Life Cycle • Cells have two major periods • Interphase • Cell grows • Cell carries on metabolic processes • Cell division • Cell replicates itself • Function is to produce more cells for growth and repair processes

  29. DNA Replication • Genetic material duplicated and readies a cell for division into two cells • Occurs toward the end of interphase • DNA uncoils and each side serves as a template Figure 3.14

  30. Events of Cell Division • Mitosis • Division of the nucleus • Results in the formation of two daughter nuclei • Cytokinesis • Division of the cytoplasm • Begins when mitosis is near completion • Results in the formation of two daughter cells

  31. Cell Life Cycle Interphase Cell growth The cell carries out normal metabolic activity (life processes) Not cell division

  32. Stages of Mitosis Prophase Nuclear membrane breaks down Spindle fibers form Centrioles move to opposite poles

  33. Stages of Mitosis Metaphase Chromosomes line up in middle of cell

  34. Stages of Mitosis Anaphase Chromosomes pull apart Chromosomes move across cell toward opposite poles

  35. Stages of Mitosis Telophase Chromosomes arrive at poles Nuclear membrane reforms Spindle fibers break down Cytokinesis- cell divides into 2 new cells

  36. Stages of Mitosis Figure 3.15

  37. Stages of Mitosis Figure 3.15(cont)

  38. Mitosis

  39. Stem and Progenitor Cells Differentiation: Cellular specialization DNA turned on/off

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