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Chapter 4

Chapter 4. Cell Structure and Function. The 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. Structure of Cells. All start out life with: Plasma membrane

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Chapter 4

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  1. Chapter 4 Cell Structure and Function

  2. The 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

  3. Structure of Cells All start out life with: • Plasma membrane • Region where DNA is stored • Cytoplasm • Two types: • Prokaryotic • Eukaryotic

  4. Prokaryotic and Eukaryotic Cells cytoplasm DNA plasma membrane Fig. 4-3a, p.52

  5. Prokaryotic and Eukaryotic Cells DNA in nucleus cytoplasm plasma membrane Fig. 4-3c, p.52

  6. Plasma Membrane • Defines the cell as a distinct entity (p52) Fig. 4-4, p.52

  7. Plasma Membrane Recognition protein Receptor protein extracellular environment lipid bilayer cytoplasm Protein pump across bilayer Protein channel across bilayer Protein pump Fig. 4-5a, p.53

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

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

  10. Membrane Proteins • Adhesion proteins • Communication proteins • Receptor proteins • Recognition proteins

  11. 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

  12. Surface-to-Volume Ratio

  13. 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

  14. Developing Cell Theory • Matthias Schleiden • Theodor Schwann • Rudolf Virchow

  15. 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

  16. 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

  17. Ocular lens enlarges primary image formed by objective lenses. path of light rays (bottom to top) to eye Objective lenses (those closest to specimen) form the primary image. Most compound light microscopes have several. prism that directs rays to ocular lens stage (holds microscope slide in position) Condenser lenses focus light rays through specimen. illuminator source of illumination (housed in the base of the microscope) Fig. 4-7a, p.54

  18. 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

  19. Limitations of Light Microscopy • Wavelengths of light are 400-750 nm • 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

  20. Different Microscopes • Different microscopes reveal different aspects of this Green Algae

  21. Size Comparison Fig. 4-9, p.55

  22. Prokaryotic Cells • Archaea and eubacteria • DNA is not enclosed in nucleus • Generally the smallest, simplest cells • No organelles

  23. Prokaryotic Structure bacterial flagellum pilus plasma membrane bacterial flagellum Most prokaryotic cells have a cell wall outside the plasma membrane, and many have a thick, jellylike capsule around the wall. cytoplasm, with ribosomes DNA in nucleoid region

  24. Eukaryotic Cells • Have a nucleus and other organelles • Eukaryotic organisms • Plants • Animals • Protistans • Fungi

  25. Plant Cell Fig. 4-13, p.58

  26. Plant Cell Features

  27. Animal Cell Fig. 4-14, p.58

  28. Animal Cell Features

  29. 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

  30. Nuclear DNA • The changing appearance of a chromosome p.61

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

  32. Components of Endomembrane System • Endoplasmic reticulum • Golgi bodies • Vesicles

  33. 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

  34. Smooth ER • A series of interconnected tubules • No ribosomes on surface • Lipids assembled inside tubules • Smooth ER of liver inactivates wastes, drugs • Sarcoplasmic reticulum of muscle is a specialized form

  35. Golgi Bodies • Put finishing touches on proteins and lipids that arrive from ER • Package finished material for shipment to final destinations • Material arrives and leaves in vesicles

  36. Vesicles • Membranous sacs that move through the cytoplasm • Lysosomes • Peroxisomes

  37. Central Vacuole • Fluid-filled organelle • Stores amino acids, sugars, wastes • As cell grows, expansion of vacuole as a result of fluid pressure forces cell wall to expand • In mature cell, central vacuole takes up 50-90 percent of cell interior

  38. Mitochondria • ATP-producing powerhouses • Double-membrane system • Carry out the most efficient energy-releasing reactions • These reactions require oxygen

  39. Mitochondria Outer mitochondrial membrane Inner mitochondrial membrane outer compartment inner compartment Fig. 4-19b, p.64

  40. Mitochondrial Structure • Outer membrane faces cytoplasm • Inner membrane folds back on itself • Membranes form two distinct compartments • ATP-making machinery is embedded in the inner mitochondrial membrane

  41. Chloroplasts Convert sunlight energy to ATP through photosynthesis

  42. chloroplast in the cytoplasm of a plant cell central vacuole Thylakoid membrane, a much-folded single flattened compartment inside the stroma two outer membranes stroma (semifluid interior) Fig. 4-20, p.65

  43. Structure of a Chloroplast • Two outer membranes around semifluid interior (stroma) – bathes inner membrane • Often, this single membrane is folded back on itself as a series of stacked, flattened disks • Each stack is called a thylakoid, which contains chlorophylls and other substances involved in photosynthesis

  44. Like Bacteria? • Both mitochondria and chloroplasts resemble bacteria • Have own DNA, RNA, and ribosomes

  45. Cell Wall Plasma membrane • Structural component that wraps around the plasma membrane • Occurs in plants, some fungi, some protistans Primary cell wall of a young plant

  46. Plant Cell Walls Secondary cell wall (3 layers) Primary cell wall

  47. Plant Cuticle • Cell secretions and waxes accumulate at plant cell surface • Semi-transparent • Restricts water loss

  48. thick, waxy cuticle at leaf surface cell of leaf epidermis photosynthetic cell inside leaf Fig. 4-22a, p.67

  49. Cell Junctions • Plants • Plasmodesmata • Animals • Tight junctions • Adhering junctions • Gap junctions plasmodesma

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