Cells

• Methods of studying cells

  • Light Microscopes
  • Electron Microscopes
  • Cell Fractionation and Ultracentrifugation
• Light Microscopes


  • Use a pair of convex glass lenses
  • Resolve images that are 0.2um apart
• Electron Microscopes


  • Can distinguish between items 0.1nm apart
  • Use a beam of electrons focused by electromagnets in a vacuum
• Magnification


  Size of image/size of real object
• Resolution


  The minimum distance apart that two objects can be distinguished as separate objects in an image
• Homogenation


  1. Blend cells in homogeniser

  2. Spin homogenate at slow speed

  3. Remove supernatant

  4. Spin supernatant at faster speed
• The whole system must be in a vacuum so living specimens cannot be observed when using electron microscopes
• A complex staining process is required which may introduce artefacts into the image when using electron microscopes
• Specimens have to be very thin, particularly for TEM so that the electrons can pass through
• Transmission Electron Microscope (TEM)


  • A beam of electrons passes through a thin section of a specimen
• Scanning Electron Microscope (SEM)


  • A beam of electrons passes across the surface and scatters
• Ultrastructure of eukaryotic cells

  • Nucleus
  • Rough endoplasmic reticulum
  • Smooth endoplasmic reticulum
  • Golgi apparatus
  • Mitochondria
  • Centrioles
  • Ribosomes
  • Lysosomes
• Nucleus


  • Double membrane called the envelope
  • Contains ~3000 nuclear pores
  • Contains chromatin and a nucleolus

  
• Rough endoplasmic reticulum


  • Series of flattened sacs enclosed by a membrane
  • Ribosomes on the surface
• Smooth endoplasmic reticulum


  • System of membrane bound sacs
  • Produces and processes lipids
• Golgi apparatus


  • Series of fluid filled, flattened & curved sacs
  • Processes and packages proteins and lipids

  
• Mitochondria


  • Oval shaped, bound by a double membrane
  • Inner membrane folded to form cristae
• Centrioles


  • Hollow cylinders containing a ring of microtubules
  • Involved in producing spindle fibres for cell division
• Ribosomes


  • Composed of two sub units
  • Site of protein production
• Lysosomes


  • Vesicles containing digestive enzymes
  • Bound by a single membrane
• Prokaryotic cells


  • Cell wall made of peptidoglycan
  • Capsule helps retain moisture
  • Plasmid is a circular piece of DNA
• Viruses


  • Non-living structures consisting of nucleic acid enclosed in a protein coat

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


  Process that produces identical daughter cells for growth and asexual reproduction

  
• Stages of the cell cycle

  • Mitosis
  • Interphase
  • Cytokinesis

  
• Stages of mitosis


  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• Binary Fission


  • Process by which prokaryotic cells divide
• Binary Fission

  1. DNA replicates and attaches to membrane

  2. Cell membrane grows and pinches inwards

  3. New cell wall forms between DNA molecules
• As viruses are non-living, they do not undergo cell division
• Biological membranes


  • Partially permeable membrane composed of phospholipids
  • Controls movement of substances in and out of the cell/organelle

  
• Fluid mosaic model


  Describes the structure of the cell membrane

  
• Cell membrane components


  • Proteins
  • Cholesterol
  • Glycolipids
  • Glycoproteins

  
• Diffusion


  • Passive movement of small, non-polar, lipid soluble molecules
• Facilitated diffusion


  • Requires a channel protein to transport polar molecules
• Osmosis


  • Diffusion of water molecules through a partially permeable membrane
• Active transport


  • Transport from low to high concentration requiring energy
• Exocytosis and endocytosis


  • Transport large particles enclosed in vesicles
• Co-Transport


  • Uses ions to move substances into and out of cells
• The rate of gas exchange by diffusion becomes more rapid as the surface area increases
• The rate of gas exchange by diffusion becomes more rapid as the diffusion distance decreases