5- Cell structure and microscopes

• Main organelles in an animal cell:

  • golgi apparatus
  • smooth endoplasmic reticulum
  • rough endoplasmic reticulum
  • nuclear envelope
  • nucleus
  • lysosome
  • mitochondria
  • ribosome
  • cytoplasm
  • cell membrane
• Ribosome:

  • site of protein synthesis
  • 80s in eukaryotic cells
  • tiny granules about 25nm in diameter
• Smooth endoplasmic reticulum:

  • has no ribosomes
  • synthesizes lipids , steroids and hormones
  • synthesizes , stores and transports carbohydrates
• Rough endoplasmic reticulum:

  • an extended system of membrane sacs
  • encrusted with ribosomes
  • synthesizes proteins
• Golgi apparatus and Golgi vesicles:

  • stacks of flattened membranes
  • modifies proteins
  • makes lysosomes
  • collects processes and sorts molecules that are then transported in golgi vesicles to other parts of the cell or outside the cell.
• lysosome:

  • contains lysozyme and contains other hydrolytic enzymes
• main organelles inside a plant cell:

  • lysosome
  • SER
  • RER
  • vacuole
  • nucleus and structure
  • ribosomes
  • cell wall
  • golgi
  • chloroplast
  • mitochondria
• Main organelles in prokaryotes:

  • flagellum- used for locomotion
  • genetic material comprises a large circle of DNA
  • cytoplasm
  • ribosomes
  • capsule
  • plasmid- small circular DNA
  • cell wall
  • cell membrane
• permanent vacuole:

  • contains cell sap and supports cell shape
• cell wall:

  • comprised of mainly cellulose in plants , chitin in fungi and cellulose or glycoproteins in algae
  • provides strength
• chloroplasts:

  • oval-shaped organelles
  • disc-like thylakoid membranes arranged in stacks called grana
  • internal fluid is called stroma
  • Light dependent reaction takes place in the thylakoid , light independent reactions take place in the stroma
• Viruses:

  • acellular and non-living
  • have genetic material
  • protein capsid
  • attachment proteins
• Light microscope:

  • uses light to form an image as the light that passes through or reflects from the surface of the specimen is seen
  • magnification up to 2000x
  • resolution to 200nm
  • living and non-living specimens can be examined
• Transmission electron microscope:

  • uses electrons to form an image
  • electrons that pass through the specimen are detected
  • magnification up to 1000000x
  • resolution to 0.2nm
  • only dead or non-living can be examined
• scanning emission electron microscope:

  • use electrons to from an image
  • electrons that are reflected from the surface of the specimen are detected
  • magnification up to 1000000x
  • resolution of 3-20nm
  • only dead or non-living
• Artefacts are undesired blemishes on a slide and can be:

  • trapped air bubbles
  • folds in thin slices of the specimen
  • chemical changes due to stains
  • contamination from other cells or tissues
• cell fractionation and ultracentrifugation:

  1. tissue is cut up and kept in a cold ,isotonic and buffered solution
  2. cut up tissue is further broken up in a homogenizer and large debris is filtered out
  3. tissue is then spun in an ultracentrifuge at low speed
  4. heavy pellet is formed usually containing nuclei
  5. spin and remove pellet and repeat till desired cell structure is left .