Cells Cell Structure and Function

1. CellsCell Structure and Function Chapter 4a

2. 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

3. 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

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

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

6. lipid bilayer fluid fluid one layer of lipids one layer of lipids Fig. 4.3, p. 52

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

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

9. oligosaccharide groups cholesterol phospholipid EXTRACELLULAR ENVIRONMENT (cytoskeletal pro-teins beneatch the plasma membrane) open channel protein gated channel proten (open) gated channel proten (closed) active transport protein RECEPTOR PROTEIN LIPID BILAYER ADHESION PROTEIN RECOGNITION PROTEIN (area of enlargment) TRANSPORT PROTEINS CYTOPLASM PLASMA MEMBRANE Fig. 4.4, p. 53

10. Why Are Cells So Small? • Surface-to-volume ratio (4r2)/(4r3/3) • 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

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. 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

13. 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

14. 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

15. Eukaryotic Cells • Have a nucleus and other organelles • Eukaryotic organisms • Plants • Animals • Protista • Fungi

16. Animal Cell Features • Plasma membrane • Nucleus • Ribosomes • Endoplasmic reticulum • Golgi body • Vesicles • Mitochondria • Cytoskeleton

17. Cell wall Central vacuole Chloroplast Plant Cell Features • Plasma membrane • Nucleus • Ribosomes • Endoplasmic reticulum • Golgi body • Vesicles • Mitochondria • Cytoskeleton

18. 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

19. Components of Nucleus Nuclear envelope Nucleoplasm Nucleolus Chromosome Chromatin

20. Nuclear Envelope • Two outer membranes (lipid bilayers) • Innermost surface has DNA attachment sites • Pores span bilayer

21. Nucleolus • Dense mass of material in nucleus • May be one or more • Cluster of DNA and proteins • Materials (mostly RNA) from which ribosomal subunits are built • Subunits must pass through nuclear pores to reach cytoplasm

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

23. 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

24. Components of Cytomembrane System Endoplasmic reticulum Golgi bodies Vesicles

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

26. 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

27. 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 that stores calcium

28. 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

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

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

31. 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

32. Mitochondrial Origins • Mitochondria resemble bacteria • Have own DNA, ribosomes • Divide on their own • May have evolved from ancient bacteria that were engulfed but not digested

33. Specialized Plant Organelles • Plastids • Central Vacuole

34. Chloroplasts Convert sunlight energy to ATP through photosynthesis

35. Photosynthesis • First stage • Occurs at thylakoid membrane • Light energy is trapped by pigments and stored as ATP • Second stage • Inside stroma, ATP energy is used to make sugars, then other carbohydrates

36. Other Plastids • Chromoplasts • No chlorophyll • Abundance of carotenoids • Color fruits and flowers red-to-yellow • Amyloplasts • No pigments • Store starch

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

38. Cytoskeleton • Present in all eukaryotic cells • Basis for cell shape and internal organization • Allows organelle movement within cells and, in some cases, cell motility

39. Cytoskeletal Elements intermediate filament microtubule microfilament

40. Microtubules • Largest elements (25 nm diameter tubes) • Composed of the protein tubulin • Arise from microtubule organizing centers (MTOCs) • Polar and dynamic • Involved in shape, motility, cell division

41. Microfilaments • Thinnest cytoskeletal elements (5-7 nm in diameter) • Composed of the protein actin • Polar and dynamic • Take part in movement, formation and maintenance of cell shape

42. Accessory Proteins • Attach to tubulin and actin • Motor proteins • Crosslinking proteins

43. Intermediate Filaments • Present only in animal cells of certain tissues • Most stable cytoskeletal elements • Six known groups • Desmins, vimentins, lamins, keratins, etc. • Different cell types usually have 1-2 different kinds

44. Mechanisms of Movement • Length of microtubules or microfilaments can change • Parallel rows of microtubules or microfilaments actively slide in a specific direction • Microtubules or microfilaments can move organelles to different parts of cell

45. Flagella and Cilia microtubule • Structures for cell motility • 9 + 2 internal structure dynein

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

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

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

49. Matrixes Between Animal Cells • Animal cells have no cell walls • Some are surrounded by a matrix of cell secretions and other material

50. Cell-to-Cell Junctions • Plants • Plasmodesmata • Animals • Tight junctions • Adhering junctions • Gap junctions plasmodesma