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Cells and Tissues

This article explores the processes of membrane transport in cells, including the two methods of transport (passive and active) and their respective mechanisms. It also discusses the concept of selective permeability and the different types of passive and active transport processes.

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Cells and Tissues

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  1. Cells and Tissues

  2. Cell Physiology: Membrane Transport • Membrane transport—movement of substances into and out of the cell • Two basic methods of transport • Passive transport • No energy is required • Active transport • Cell must provide metabolic energy (ATP)

  3. Solutions and Transport • Solution—homogeneous mixture of two or more components • Solvent—dissolving medium; typically water in the body • Solutes—components in smaller quantities within a solution • Intracellular fluid—nucleoplasm and cytosol • Interstitial fluid—fluid on the exterior of the cell

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

  5. Passive Transport Processes • Diffusion • Particles tend to distribute themselves evenly within a solution • Movement is from high concentration to low concentration, or down a concentration gradient Figure 3.9

  6. Passive Transport Processes • Types of diffusion • Simple diffusion • An unassisted process • Solutes are lipid-soluble materials or small enough to pass through membrane pores

  7. Passive Transport Processes Figure 3.10a

  8. Passive Transport Processes • Types of diffusion (continued) • Osmosis—simple diffusion of water • Highly polar water molecules easily cross the plasma membrane through aquaporins

  9. Passive Transport Processes Figure 3.10d

  10. Passive Transport Processes • Facilitated diffusion • Substances require a protein carrier for passive transport • Transports lipid-insoluble and large substances

  11. Passive Transport Processes Figure 3.10b–c

  12. Passive Transport Processes • Filtration • Water and solutes are forced through a membrane by fluid, or hydrostatic pressure • A pressure gradient must exist • Solute-containing fluid is pushed from a high-pressure area to a lower pressure area

  13. Active Transport Processes • Substances are transported that are unable to pass by diffusion • Substances may be too large • Substances may not be able to dissolve in the fat core of the membrane • Substances may have to move against a concentration gradient • ATP is used for transport

  14. Active Transport Processes • Two common forms of active transport • Active transport (solute pumping) • Vesicular transport • Exocytosis • Endocytosis • Phagocytosis • Pinocytosis

  15. Active Transport Processes • Active transport (solute pumping) • Amino acids, some sugars, and ions are transported by protein carriers called solute pumps • ATP energizes protein carriers • In most cases, substances are moved against concentration gradients

  16. Extracellular fluid Na+ K+ Na+ P Na+ P Na+ Na+ K+ K+ Na+ P K+ ATP ADP Loss of phosphate restoresthe original conformation ofthe pump protein. K+ isreleased to the cytoplasm andNa+ sites are ready to bind Na+again; the cycle repeats. Binding of cytoplasmic Na+to the pump proteinstimulates phosphorylationby ATP, which causes thepump protein to change itsshape. The shape change expelsNa+ to the outside.Extracellular K+ binds,causing release of thephosphate group. Cytoplasm Figure 3.11

  17. Extracellular fluid Na+ Na+ Na+ P ATP ADP Binding of cytoplasmic Na+to the pump proteinstimulates phosphorylationby ATP, which causes thepump protein to change itsshape. Cytoplasm Figure 3.11, step 1

  18. Extracellular fluid Na+ K+ Na+ P Na+ P Na+ Na+ K+ Na+ P ATP ADP Binding of cytoplasmic Na+to the pump proteinstimulates phosphorylationby ATP, which causes thepump protein to change itsshape. The shape change expelsNa+ to the outside.Extracellular K+ binds,causing release of thephosphate group. Cytoplasm Figure 3.11, step 2

  19. Extracellular fluid Na+ K+ Na+ P Na+ P Na+ Na+ K+ K+ Na+ P K+ ATP ADP Loss of phosphate restoresthe original conformation ofthe pump protein. K+ isreleased to the cytoplasm andNa+ sites are ready to bind Na+again; the cycle repeats. Binding of cytoplasmic Na+to the pump proteinstimulates phosphorylationby ATP, which causes thepump protein to change itsshape. The shape change expelsNa+ to the outside.Extracellular K+ binds,causing release of thephosphate group. Cytoplasm Figure 3.11, step 3

  20. Active Transport Processes • Vesicular 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 emptied to the outside

  21. Active Transport Processes: Exocytosis Figure 3.12a

  22. Active Transport Processes: Exocytosis Figure 3.12b

  23. Active Transport Processes • Vesicular transport (continued) • Endocytosis • Extracellular substances are engulfed by being enclosed in a membranous vescicle • Types of endocytosis • Phagocytosis—“cell eating” • Pinocytosis—“cell drinking”

  24. Extracellularfluid Extracellularfluid Cytoplasm Plasmamembrane Pit Recycling of membraneand receptors (if present)to plasma membrane Transport to plasmamembrane andexocytosis ofvesicle contents Ingestedsubstance Vesicle Lysosome Detachmentof vesicle Release ofcontents tocytoplasm Vesicle containingingested material Plasmamembrane Vesicle fusingwith lysosomefor digestion (a) Active Transport Processes: Endocytosis Figure 3.13a

  25. Extracellularfluid Extracellularfluid Plasmamembrane Cytoplasm Pit Ingestedsubstance Plasmamembrane (a) Active Transport Processes: Endocytosis Figure 3.13a, step 1

  26. Extracellularfluid Extracellularfluid Plasmamembrane Cytoplasm Pit Ingestedsubstance Detachmentof vesicle Vesicle containingingested material Plasmamembrane (a) Active Transport Processes: Endocytosis Figure 3.13a, step 2

  27. Extracellularfluid Extracellularfluid Plasmamembrane Cytoplasm Pit Ingestedsubstance Vesicle Lysosome Detachmentof vesicle Vesicle containingingested material Plasmamembrane Vesicle fusingwith lysosomefor digestion (a) Active Transport Processes: Endocytosis Figure 3.13a, step 3

  28. Extracellularfluid Extracellularfluid Plasmamembrane Cytoplasm Pit Ingestedsubstance Vesicle Lysosome Detachmentof vesicle Release ofcontents tocytoplasm Vesicle containingingested material Plasmamembrane Vesicle fusingwith lysosomefor digestion (a) Active Transport Processes: Endocytosis Figure 3.13a, step 4

  29. Extracellularfluid Extracellularfluid Plasmamembrane Cytoplasm Pit Transport to plasmamembrane andexocytosis ofvesicle contents Ingestedsubstance Vesicle Lysosome Detachmentof vesicle Release ofcontents tocytoplasm Vesicle containingingested material Plasmamembrane Vesicle fusingwith lysosomefor digestion (a) Active Transport Processes: Endocytosis Figure 3.13a, step 5

  30. Extracellularfluid Extracellularfluid Plasmamembrane Cytoplasm Pit Recycling of membraneand receptors (if present)to plasma membrane Transport to plasmamembrane andexocytosis ofvesicle contents Ingestedsubstance Vesicle Lysosome Detachmentof vesicle Release ofcontents tocytoplasm Vesicle containingingested material Plasmamembrane Vesicle fusingwith lysosomefor digestion (a) Active Transport Processes: Endocytosis Figure 3.13a, step 6

  31. Active Transport Processes: Endocytosis Figure 3.13b–c

  32. Active Transport Processes

  33. 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

  34. DNA Replication • Genetic material is 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

  35. DNA Replication Figure 3.14

  36. 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

  37. Stages of Mitosis • Prophase • First part of cell division • Centrioles migrate to the poles to direct assembly of mitotic spindle fibers • DNA appears as double-stranded chromosomes • Nuclear envelope breaks down and disappears

  38. Stages of Mitosis • Metaphase • Chromosomes are aligned in the center of the cell on the metaphase plate

  39. Stages of Mitosis • Anaphase • Chromosomes are pulled apart and toward the opposite ends of the cell • Cell begins to elongate

  40. Stages of Mitosis • Telophase • Chromosomes uncoil to become chromatin • Nuclear envelope reforms around chromatin • Spindles break down and disappear

  41. Stages of Mitosis • Cytokinesis • Begins during late anaphase and completes during telophase • A cleavage furrow forms to pinch the cells into two parts

  42. Centrioles Spindlemicrotubules Centrioles Chromatin Centromere Centromere Formingmitoticspindle Plasmamembrane Chromosome,consisting of twosister chromatids Fragments ofnuclear envelope Spindlepole Nuclearenvelope Nucleolus Early prophase Interphase Late prophase Nucleolusforming Metaphaseplate Spindle Cleavagefurrow Nuclearenvelopeforming Sisterchromatids Daughterchromosomes Telophase and cytokinesis Metaphase Anaphase Stages of Mitosis Figure 3.15

  43. Centrioles Chromatin Plasmamembrane Nuclearenvelope Nucleolus Interphase Stages of Mitosis Figure 3.15, step 1

  44. Centrioles Centrioles Chromatin Centromere Formingmitoticspindle Plasmamembrane Chromosome,consisting of twosister chromatids Nuclearenvelope Nucleolus Interphase Early prophase Stages of Mitosis Figure 3.15, step 2

  45. Centrioles Spindlemicrotubules Centrioles Chromatin Centromere Centromere Formingmitoticspindle Plasmamembrane Chromosome,consisting of twosister chromatids Fragments ofnuclear envelope Spindlepole Nuclearenvelope Nucleolus Interphase Early prophase Late prophase Stages of Mitosis Figure 3.15, step 3

  46. Metaphaseplate Spindle Sisterchromatids Metaphase Stages of Mitosis Figure 3.15, step 4

  47. Metaphaseplate Spindle Daughterchromosomes Sisterchromatids Metaphase Anaphase Stages of Mitosis Figure 3.15, step 5

  48. Nucleolusforming Metaphaseplate Spindle Cleavagefurrow Nuclearenvelopeforming Daughterchromosomes Sisterchromatids Metaphase Anaphase Telophase and cytokinesis Stages of Mitosis Figure 3.15, step 6

  49. Centrioles Spindlemicrotubules Centrioles Chromatin Centromere Centromere Formingmitoticspindle Plasmamembrane Chromosome,consisting of twosister chromatids Fragments ofnuclear envelope Spindlepole Nuclearenvelope Nucleolus Early prophase Interphase Late prophase Nucleolusforming Metaphaseplate Spindle Cleavagefurrow Nuclearenvelopeforming Sisterchromatids Daughterchromosomes Telophase and cytokinesis Metaphase Anaphase Stages of Mitosis Figure 3.15, step 7

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