chapter 5

• Chapter 5 Key Concepts


  • 5.1 Cells Are the Fundamental Units of Life
  • 5.2 Prokaryotic Cells Are the Simplest Cells
  • 5.3 Eukaryotic Cells Contain Organelles
  • 5.4 Extracellular Structures Have Important Roles
  • 5.5 Eukaryotic Cells Evolved in Several Steps
• Endosymbiotic theory


  As presented on Slides 26-27 in this presentation
• Cell


  The basic unit of life - all living things are made up of cells
• Cell theory


  An important unifying theory of biology
• Implications of the cell theory


  • Functions of all cells are similar
  • Life is continuous
  • Origin of life was the origin of cells
• Cells


  • Small (mostly)
  • Exceptions: bird eggs, some algae and bacteria
• Epulopiscium fishelsoni


  A single cell ranges from 0.5 to 10 cm tall
• Acetabularia (Algae)


  Unicellular green algae
• Why are cells small?


  High surface-area-to-volume ratio is essential for many cell functions
• As a cell volume increases


  Chemical activity increases, along with the need for resources and waste removal
• Surface area


  The limiting factor on the capability of a cell to import resources and export wastes
• Large organisms typically consist of many small cells
• Changes in cell shape

  • To increase the surface-area-to-volume ratio
• Changes in cell shape

  • Neurons
  • Red blood cells
  • Small intestine lining cells
• Magnification


  Ratio of an object's image size to its real size
• Resolution


  Measure of the clarity of image, or the minimum distance of two distinguishable points
• Contrast


  Differences in intensity between two objects or between an object and its background
• Staining increases contrast
• Two basic types of microscopes


  • Light microscopes
  • Electron microscopes
• Light microscopes


  Use glass lenses and light, resolution limit = 0.2 μm
• Electron microscopes


  Use electromagnets to focus an electron beam, resolution limit = 0.2 nm
• Scanning electron microscopes


  Beam of electrons onto the surface of a specimen
• Transmission electron microscopes


  Focus a beam of electrons through a specimen to see the internal structure of cells
• Cell membrane


  The outer boundary of every cell, has similar structure in all cells
• Cell membrane


  A phospholipid bilayer with embedded proteins
• Cell membrane function


  • Selectively permeable barrier
  • Allows cells to maintain a constant internal environment (homeostasis)
  • Important in communication and receiving signals
  • Often has proteins for binding and adhering to adjacent cells
• Two types of cells


  • Prokaryotic
  • Eukaryotic
• Prokaryotic cells


  • Smaller and more structurally simple
• Eukaryotic cells


  • Larger and structurally complex
  • DNA in a nucleus
  • Membrane-bound organelles
• Prokaryotic cell characteristics


  • Enclosed by a cell membrane
  • DNA located in a region called the nucleoid
  • Cytoplasm: the rest of the cell contents
  • Ribosomes: sites of protein synthesis
  • Most have cell walls, usually with peptidoglycan
  • Some have a slimy capsule made of polysaccharides
  • Some have flagella for motion, and fimbriae for adhesion to surfaces or other bacteria
• Cytoplasm


  The space between the plasma membrane and the nucleus
• Cytosol


  Jelly like fluid of the cell
• Eukaryotes are about 10 times larger than prokaryotes
• Nucleus


  • Usually the largest organelle
  • Contains most of the DNA
  • Site of DNA replication
  • Site where gene transcription is turned on or off
  • Assembly of ribosomes begins in a region called the nucleolus
  • Surrounded by the nuclear envelope, a double membrane, with nuclear pores to control movement of molecules across the envelope
  • DNA combines with proteins to form chromatin in long, thin threads called chromosomes
  • Before cell division, chromatin condenses, and individual chromosomes are visible in the light microscope
• Endomembrane system


  • An interconnected system of organelles that includes: plasma membrane, nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, and lysosomes
  • Tiny, membrane-surrounded vesicles shuttle substances between the various components
  • Rough endoplasmic reticulum (RER): Ribosomes are attached, newly made proteins enter the RER lumen, are modified, folded, and transported to other regions
• Lysosomes


  • Membranous sac of hydrolytic enzymes that can digest macromolecules
  • Very acidic
  • 2 processes that utilize lysosomes: Phagocytosis and Autophagy
• Mitochondria


  • In all eukaryotic cells (except for some parasites that steal energy molecules from their hosts)
  • Have a smooth outer membrane and an inner membrane folded into cristae
  • Two compartments: Intermembrane space and Matrix
• Chloroplasts


  • The sites of photosynthesis, the process of converting light energy into chemical energy
  • Found in leaves and other green organs of plants and in algae
  • Structure includes thylakoids, granum, and stroma: the internal fluid
• Endosymbiotic theory


  Evolution of eukaryotic structures
• Eukaryotic cells first appeared about 1.5 billion years ago