topic 2

• Light microscope


  Uses a pair of convex glass lenses that can resolve images 0.2um apart
• Electron microscope


  Can distinguish between items 0.1nm apart
• Magnification


  Size of image/size of real object
• Resolution


  Minimum distance apart that two objects can be distinguished as separate objects in an image
• Transmission Electron Microscope (TEM)


  • Beam of electrons passes through a thin section of a specimen, areas that absorb the electrons appear darker
• Scanning Electron Microscope (SEM)

  • Beam of electrons passes across the surface and scatters, the pattern of scattering builds up a 3D image
• Limitations of electron microscopes

  • Whole system must be in a vacuum so living specimens cannot be observed
  • Complex staining process required which may introduce artefacts
  • Specimens have to be very thin, particularly for TEM
  • SEM has lower resolving power than TEM
• Cell fractionation


  1. Cells are blended in a homogeniser

  2. Homogenate is placed in a centrifuge and spun at increasing speeds to separate organelles

  3. Heaviest organelles sediment first

  
• Homogenate


  Fluid resulting from blending cells in a homogeniser
• Supernatant


  Fluid at the top after centrifugation, containing the next lightest organelles
• Pellet


  Sediment at the bottom after centrifugation, containing the heaviest organelles
• Homogenate is placed in a cold, buffered solution to prevent organelle bursting, inactivate enzymes, and maintain pH
• Ultrastructure of eukaryotic cells

  • Nucleus
  • Rough endoplasmic reticulum
  • Smooth endoplasmic reticulum
  • Golgi apparatus
  • Mitochondria
  • Centrioles
  • Ribosomes
  • Lysosomes
• Structures in prokaryotic cells

  • Cell wall
  • Capsule
  • Plasmid
  • Flagellum
  • Pili
  • Ribosomes
  • Mesosomes

  
• Virus


  Non-living structure consisting of nucleic acid (DNA or RNA) enclosed in a protective protein coat (capsid), sometimes with a lipid envelope

  
• Cells of multicellular organisms are organised into tissues, tissues into organs, and organs into systems
• Mitosis


  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase

  
• Interphase


  Cell grows and prepares to divide, chromosomes and some organelles are replicated, chromosomes begin to condense

  
• Cytokinesis


  Parent and replicated organelles move to opposite sides of the cell, cytoplasm divides to produce two daughter cells

  
• Importance of mitosis


  • Growth
  • Repair
  • Reproduction in single-celled organisms
• Binary fission


  1. Circular DNA replicates and attaches to cell membrane

  2. Cell membrane grows inward, dividing cytoplasm

  3. New cell wall forms, producing two identical daughter cells
• Fluid mosaic model


  Structure of biological membranes, composed of a sea of phospholipids with protein molecules between them

  
• Components of cell membrane

  • Phospholipids
  • Proteins (intrinsic and extrinsic)
  • Cholesterol
  • Glycolipids
  • Glycoproteins
• Diffusion


  Passive movement of small, non-polar, lipid-soluble molecules from high to low concentration
• Facilitated diffusion


  Movement of polar, charged, and water-soluble molecules across the membrane using channel proteins
• Osmosis


  Diffusion of water molecules from high to low water potential through a partially permeable membrane
• Active transport


  Movement of molecules from low to high concentration using energy in the form of ATP
• Exocytosis and endocytosis


  Transport of large particles enclosed in vesicles, either out of or into the cell

  
• Co-transport


  Use of ions to move substances into and out of cells, particularly in epithelial cells of the ileum
• Factors that increase the rate of gas exchange by diffusion

  • Increased surface area
  • Decreased diffusion distance
• Transport across cell membrane

  1. Active transport

  2. Exocytosis

  3. Endocytosis

  4. Co-transport
• Active transport


  • Requires energy in the form of ATP
• Exocytosis


  Transport of large particles out of the cell in vesicles

  
• Endocytosis


  Transport of large particles into the cell in vesicles

  
• Co-transport


  Uses ions to move substances into and out of cells, particularly in epithelial cells of the ileum
• Sodium and potassium ions pumped out of epithelial cell

  Causes these ions to move in from the lumen by facilitated diffusion, which at the same time brings glucose and amino acids into the cell
• Factors that increase rate of gas exchange by diffusion

  • Increased surface area
  • Decreased diffusion distance
  • Steeper diffusion gradient
  • Increased temperature
• Bacteria


  Prokaryotic cells with circular DNA, do not require a host to survive
• Viruses


  Consist of nucleic acid enclosed in a protein coat, can have DNA or RNA, entirely dependent on hosts

  
• Differences between bacteria and viruses

  • Bacteria are prokaryotic, viruses consist of nucleic acid and protein
  • Bacteria do not require a host, viruses are dependent on hosts
  • Viruses are significantly smaller than bacteria
  • Bacteria have cell membrane, wall, cytoplasm and organelles, viruses have no such structures