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A Tour of the Cell: The Microscopic World and Structure of Cells

Explore the fascinating world of cells and their structures through the lens of a microscope. Learn about the different types of cells, the pioneers of cell discovery, and the functions of organelles within cells. Discover how DNA controls cellular processes and how the endomembrane system manufactures and distributes cellular products.

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A Tour of the Cell: The Microscopic World and Structure of Cells

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  1. CHAPTER 4 A Tour of the Cell

  2. THE MICROSCOPIC WORLD OF CELLS • Cells are the building blocks of all life • Cells must be tiny for materials to move in and out of them fast enough to meet the cell’s metabolic needs

  3. Organisms are either: • Single-celled (unicellular), such as most bacteria and protists • Multi-celled (multi-cellular), such as plants, animals, and most fungi

  4. Leeuwenhoek What is he known for? Developed the first microscope.

  5. This is Leeuwenhoek’s first microscope.

  6. Englishman Robert Hooke First to use the word: “Cells.”

  7. Unfortunately, he was looking at cork cells which aren’t living structures but the remains of living cells

  8. Robert Brown in 1833, Scottish Scientist who discovered the nucleus of cells

  9. Matthias Schleiden Theodor Schwann “First to see plantcells” “First to see animal cells”

  10. “The Cell Theory” • All living things are made of cells • Cells are the basic units of structure and function in living things • All cells come from preexisting cells Rudolph Virchow

  11. Microscopes as Windows to Cells • The light microscope is used by many scientists • Light passes through the specimen • Lenses enlarge, or magnify, the image (a) Light micrograph (LM) of a white blood cell (stained purple) surrounded by red blood cells

  12. The electron microscope (EM) uses a beam of electrons • It has a higher resolving power than the light microscope

  13. The electron microscope can magnify up to 100,000X Human height Length of some nerve and muscle cells Chicken egg Unaided eye Frog eggs • Such power reveals the diverse parts within a cell Light microscope Plant and animal cells Nucleus Most bacteria Mitochondrion Electron microscope Smallest bacteria Viruses Ribosomes Proteins Lipids Small molecules Atoms

  14. SEM • The scanning electron microscope (SEM) is used to study the detailed architecture of the surface of a cell (b) Scanning electron micrograph (SEM) of cilia (above) And a white blood cell

  15. TEM • The transmission electron microscope (TEM) is useful for exploring the internal structure of a cell (c) Transmission electron micrograph (TEM) of a white blood cell & cilial

  16. The Two Major Categories of Cells • The countless cells on earth fall into two categories • Prokaryotic cells • Eukaryotic cells

  17. Prokaryotic and eukaryotic cells differ in several respects Prokaryotic cell Nucleoid region Eukaryotic cell Organelles Nucleus

  18. Prokaryotic cells • Are smaller than eukaryotic cells • Lack internal structures surrounded by membranes • Lack a nucleus

  19. Prokaryotic flagella Nucleoid region (DNA) Ribosomes Plasma membrane Cell wall Capsule Pili

  20. A Generic Animal Cell

  21. An idealized plant cell

  22. Structure and Function of the Nucleus • The nucleus is bordered by a double membrane called the nuclear envelope • It contains chromatin -a DNA-protein structure • It contains a nucleolus - which produces ribosomal parts

  23. Ribosomes • Ribosomes build all the cell’s proteins • Are not membrane bound

  24. How DNA Controls the Cell • DNA controls the cell by transferring its coded information into RNA DNA 1 Synthesis of mRNA in the nucleus mRNA • The information in the RNA is used to make proteins Nucleus Cytoplasm mRNA 2 Movement of mRNA into cytoplasm via nuclear pore Ribosome 3 Synthesis of protein in the cytoplasm Protein

  25. THE ENDOMEMBRANE SYSTEM: MANUFACTURING AND DISTRIBUTING CELLULAR PRODUCTS • Many of the membranous organelles in the cell belong to the endomembrane system • Endoplasmic reticulum - rough and smooth • Golgi Apparatus • Lysosomes • Vacuoles

  26. The Endoplasmic Reticulum • The endoplasmic reticulum (ER) Nuclear envelope • Greek for ‘network within a cell’ • Produces an enormous variety of molecules • Is composed of smooth and rough ER Ribosomes Rough ER Smooth ER

  27. Rough ER • The “roughness” of the rough ER is due to ribosomes that stud the outside of the ER membrane

  28. The functions of the rough ER include • Producing proteins • Producing new membrane

  29. After the rough ER synthesizes a molecule it packages the molecule into transport vesicles 1

  30. Smooth ER • The smooth ER lacks the surface ribosomes of ER • Produces lipids, including steroids and sex hormones • Regulates sugar • Detoxifies drugs • Stores calcium

  31. The Golgi Apparatus • The Golgi apparatus • Works in partnership with the ER • Refines, stores, and distributes the products of cells Transport vesicle from ER “Receiving” side of Golgi apparatus Golgi apparatus New vesicle forming Transport vesicle from the Golgi “Shipping” side of Golgi apparatus Plasma membrane

  32. Lysosomes • A lysosome is a membrane-enclosed sac • Greek for ‘breakdown body’ • It contains digestive enzymes • Isolated by membrane • The enzymes break down • Macromolecules • Old organelles

  33. Lysosomes have several types of digestive functions • They exit the Golgi apparatus

  34. They fuse with food vacuoles to digest the food

  35. They fuse with old organelles to recycle parts • Digest bacteria in white blood cells

  36. Vacuoles • Vacuoles are membranous sacs • Two types are the contractile vacuoles of protists and the central vacuoles of plants Central vacuole Contractile vacuoles (a) Contractile vacuoles in a protist (b) Central vacuole in a plant cell Figure 4.15

  37. CHLOROPLASTS AND MITOCHONDRIA: ENERGY CONVERSION • Cells require a constant energy supply to do all the work of life

  38. CHLOROPLASTS • Chloroplasts are the sites of photosynthesis, the conversion of light energy to chemical energy Inner and outer membranes of envelope Granum Space between membranes Stroma (fluid in chloroplast) Figure 4.17

  39. Mitochondria • Mitochondria are the sites of cellular respiration, which involves the production of ATP from food molecules Outer membrane Inner membrane Cristae Matrix Space between membranes Figure 4.18

  40. THE CYTOSKELETON:CELL SHAPE AND MOVEMENT • The cytoskeleton is an infrastructure of the cell consisting of a network of fibers • Microfilaments - small threads • Intermediate filaments - ropelike • Microtubules - small tubes

  41. Maintaining Cell Shape • One function of the cytoskeleton • Provide mechanical support to the cell and maintain its shape

  42. Figure4.9x

  43. The cytoskeleton can change the shape of a cell • This allows cells like amoebae to move

  44. Cilia and Flagella • Cilia and flagella are motile appendages

  45. Flagella propel the cell in a whip-like motion • Cilia move in a coordinated back-and-forth motion Figure 4.20A, B

  46. Some cilia or flagella extend from nonmoving cells • The human windpipe is lined with cilia • Smoking damages the cilia

  47. CELL SURFACES:PROTECTION, SUPPORT, AND CELL-CELL INTERACTIONS • Most cells secrete materials that are external to the plasma membrane • This extra cellular matrix • Regulates • Protects • Supports

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