Cell Biology

• Light Microscope


  • Uses beam of light to illuminate specimen
  • Can only see basic structure
  • Resolution and magnification too low to see small structures
• Electron Microscope


  • Uses beam of electrons to visualise specimen
  • Can see ultrastructure of cell e.g. mitochondria, RER
  • Higher resolution and magnification
  • Specimen is always dead
• Light microscope retains natural colours, electron microscope only produces black and white images
• Light microscope is portable, electron microscope is not portable
• Resolution


  Ability to see detail and distinguish between nearby structures
• Magnification


  By how much the image is enlarged = eyepiece magnification x objective lens
• Eyepiece Graticule


  Glass disc fitted into eyepiece with fine scale [0-100] of arbitrary units
• Stage Micrometer


  Slide marked with fine divisions, used to calibrate Eyepiece Graticule
• Preparing temporary slides


  1. Sectioning: cutting specimen

  2. Fixation: place in liquid to preserve state

  3. Staining: to better visualise specimen

  4. Mounting: place on slide with drop of liquid and cover slip
• Irrigation Technique


  Staining after placing coverslip by putting drop of stain on one end and drawing it over the specimen
• Basic Stains


  • Methylene blue
  • Safranin
  • Crystal violet
• Basic stains are negatively charged molecules that stain things like nucleic acids and some proteins
• Acidic Stains


  • Eosin
  • Rose bengal
• Acidic stains are positively charged molecules that stain some proteins
• Cell Theory


  • All living organisms made up of cells
  • All cells come from pre-existing cells
  • Cells capable of self-reproduction
• Viruses are considered borderline between living and non-living since they are acellular
• Cell Differentiation


  • Meristematic cells retain ability to divide
  • Specialised cells have division of labour
• Prokaryotic Cells


  • 1-10 μm in size
  • High surface area to volume ratio for efficient diffusion and reactions
• Eukaryotic Cells


  • 10-100 μm in size
  • Compensate for larger size and lower surface area to volume ratio through compartmentalisation and organelles
• Components of Prokaryotic Cells

  • Circular DNA in nucleoid region
  • Plasmids
  • 70S ribosomes
  • Cell membrane with infoldings
  • Peptidoglycan cell wall
  • Slime capsule
  • Flagellum
  • Pili
• Prokaryotic Reproduction


  Asexual binary fission to produce genetically identical daughter cells
• Prokaryotic Conjugation


  Only way to introduce genetic diversity, involves transfer of plasmid DNA between cells
• Prokaryotic Cell Shapes


  • Bacillus (rods)
  • Coccus (spheres)
  • Spirilla (spirals)
• Prokaryotic Metabolisms


  • Anaerobic
  • Aerobic (with membrane infoldings)
  • Obligate anaerobes
  • Facultative anaerobes
• Prokaryotic Nutritional Modes


  • Photoautotrophs
  • Chemoautotrophs
  • Photoheterotrophs
  • Chemoheterotrophs
• Gram Staining


  Gram-positive: thick peptidoglycan wall, retain crystal violet stain

  Gram-negative: thin peptidoglycan wall, lose crystal violet stain when washed in ethanol
• Components of Eukaryotic Cells

  • DNA enclosed in double-membraned nucleus
  • Linear chromosomes wound around histones
  • Nucleolus
  • 80S ribosomes
  • Endoplasmic reticulum
  • Golgi apparatus
  • Lysosomes
  • Peroxisomes
  • Plant vacuole
  • Cell wall
  • Cytoplasm
  • Mitochondria
  • Plastids
  • Cytoskeleton
• Endoplasmic Reticulum


  Network of membranes continuous with nuclear envelope

  RER: flattened cisternae with embedded ribosomes for protein synthesis

  SER: tubular cisternae without ribosomes, for lipid synthesis and transport
• Golgi Apparatus


  Cis/Receiving face: fused incoming vesicles from ER

  Trans/Shipping face: secretes substances in vesicles
• Lysosomes


  Vesicles containing digestive/hydrolytic enzymes, optimum pH <7

  Involved in autophagy, cell digestion, and extracellular secretion
• Peroxisomes


  Contain enzymes for oxidation of fatty acids and alcohols
• Plant Cell Wall


  Made of cellulose, pectin, and lignin

  Provides tensile strength, prevents cell lysis, limits growth, and facilitates water transport
• Cytoplasm


  70% water and solutes, can be in sol (liquid) or gel (viscous) state

  Cytoplasmic streaming allows locomotion
• Mitochondria


  Inner membrane folded into cristae for increased surface area

  Circular DNA and 70S ribosomes, site of aerobic respiration
• Plastids


  Double-membraned plant organelles, including chloroplasts for photosynthesis
• Endosymbiotic Theory


  Mitochondria and chloroplasts originated from engulfed prokaryotic cells
• Components of Cytoskeleton


  • Microtubules
  • Microfilaments
  • Intermediate filaments
• Microtubules


  Columns of tubulin subunits, involved in organelle movement and cell division
• Microfilaments


  Two intertwined strands of F-actin, involved in muscular contraction and cytoplasmic streaming
• Intermediate Filaments


  Protein fibres that support the plasma membrane and nuclear envelope