cell structure

• ultrastructure - detail revealed by the electron microscope
• how to use the light microscope

  1. place slide on stage and clip in
  2. using low power lens, calibrate using coarse focus
  3. switch to medium power lens, adjust using fine focus
  4. switch to high power lens, adjust using fine focus
• staining - colour chemicals that bind to molecules in a specimen

  uses - provides contrast, increases visibility

  examples - methylene blue, light green
• differential staining - using more than one stain to highlight different structures in the same specimen
• magnification - the number of times larger the image is compared to the actual object
• resolution - the ability to distinguish between very close points together, the higher the resolution the easier is to distinguish
• eyepiece graticule - a scale in the eyepiece divided into 100 subunits
• stage micrometer - a microscope slide used to measure specimen
• calculations

  • low power: 1 EPU = 25µm
  • medium power: 1 EPU = 10 µm
  • high power: 1 EPU = 2.5µm
• laser scanning confocal microscopes

  • a laser scans a specimen tagged with fluorescent dye
  • laser causes the dye to give off fluorescent light
  • light is focused through a pinhole
  • can see images at multiple depths
  • create 3d image
  • uses - endoscopes
  • high resolution
  • whole specimens examined
• electron microscopes

  • beam of electrons = 0.004nm
  • samples must be vacuum sealed
  • air pumped out and electrons fired down a series of electromagnetic lenses
  • black and white image produced
• scanning electron microscope

  • can view whole specimens
  • thinly coated with gold
  • 3D image
  • 200000 magnification
  • 2nm resolution
• transmission electron microscope

  • sample sectioned thinly
  • electrons transmitted through specimens
  • 2D image
  • 2000000 magnification
  • 0.2nm resolution
• light microscope

  • 2000 magnification
  • 200nm resolution
  • coloured image
• nucleus

  • nucleoplasm - contains chromatin
  • nuclear envelope -double membrane and encloses dna
  • nuclear pores - entry and exit of molecules for replication
  • nucleolus - manufactures ribosomes
• endoplasmic reticulum

  • cisternae, membrane bound sacs - allow for transport
  • rough, contains ribosomes - protein synthesis and transport
  • smooth - lipid and steroid synthesis and transport
• ribosomes

  • 2 subunits of rna and protein
  • either prokaryotic (small) 70s eukaryotic (larger) 80s
  • protein synthesis
• Golgi apparatus

  • flattened sack of membrane bound cavities - modifies proteins, packages proteins into vesicles
  • secretory vesicle - release hormones or enzymes
• lysosomes

  • hydrolytic enzymes - isolate potentially harmful cells, apoptosis, phagocytosis
• mitochondria

  • double membrane
  • cristae - increase sa
  • small ribosomes
  • circular dna
  • enzymes
• chloroplasts

  • double membrane
  • thylakoids stacked into grana
  • stroma contains: lipid droplets, starch molecules, dna, small ribosomes
• centrioles

  • 2 centrioles in all animal cells
  • 9 sets of 3 microtubules
  • form spindle fibres during cell division
• cytoskeleton

  • composed of: microtubules, microfilaments, intermediate filaments
  • function: support organelle position, enable movement of organelles, strengthen cell and maintain shape of cell
• cilia and flagella

  • 2 central tubules surrounded by 9 pairs
  • short threadlike projections = cilia
  • long whiplike projections = flagella
  • function: cilia in bronchi waft mucus and waft ovum towards uterus
• vacuole

  • cell sap in the tonoplast
  • maintains support for cell wall
  • storage of mineral ions
• plant cell wall

  • made of cellulose - turgidity
  • rigid and permeable - prevents bursting
  • modified by lignin
  • pores penetrated by plasmodesmata - line neighbouring cells
  • middle lamella - cements cells together
• structures always inside a prokaryote

  • cell surface membrane
  • cytoskeleton
  • circular DNA
  • nucleoid
  • cytoplasm
  • small ribosomes
  • peptidoglycan cell wall
• sometimes present inside a prokaryote

  • flagellum
  • folding membrane
  • mesosome - formation of cell wall
  • slime capsule
  • plasmid
  • pili - acts as anchor during asexual reproduction