Cell structure

• How does a light microscope work?

  -uses a number of lenses to produce an image that can be viewed directly through an eye piece

  -light passes from a bulb under the stage, through a condenser lens and then through the specimen

  -this beam of light is passed through an objective lens (x4,x10,x40) then an eyepiece lens (x10)
• Overall magnification equation


  overall magnification = objective lens x eyepiece lens magnification
• how does a transmission electron microscope (TEM) work?

  -uses electromagnets to focus a beam of electrons, which is transmitted through the specimen

  -Denser parts of the specimen absorb more electrons, which makes them look darker on the image you end up with creating a contrast.
• how does a scanning electron microscope (SEM) work?

  -an electron beam is scanned across the specimen

  -The electrons don't pass through the specimen, they bounce off and are detected at multiple detectors.
• what are the advantages of electron microscopes

  -the resolution is 0.1nm (2000x more than the light microscope)

  -can produce detailed images of structures inside cells

  -produces a 3D image
• what are the disadvantages of electron microscopes

  -electron beams are deflected by air molecules, so the sample has to be placed in a vacuum (specimen is not living)

  -electron microscopes are extremely expensive

  -preparing samples and using the electron microscope both require a high degree of skill and training
• magnification defeniton


  the number of times greater an image is than the object itself
• resolution defenition


  the ability to distinguish two separate points as distinct from each other
• preparation of a microscope slide

  -Material needs to be stained to allow the specimen to be seen under the microscope

  -Images are produced because some parts of the object absorb more light/electrons than others to create contrast, but sometimes the object being viewed is completely transparent - this makes the whole thing look white because the light rays/electrons pass straight through

  -This problem is solved by staining the specimen
• what stains DNA dark red

  Acetic orcein
• what stains bacteria cell walls

  Genetian Violet
• why are some microscope specimens embedded in wax

  to prevent the distortion of the structure when being cut
• why are electron microscopes stained with heavy metals (like lead)


  to scatter the electrons and create contrasr
• magnification formula


  magnification = image size / actual size

  
  

  actual size = image size / magnification
• Nucleus description


  -largest organelle (10-20 um)

  -roughly spherical

  -double membrane bound
• nucleus function


  -contains chromatin (mixture of DNA and associated proteins)

  -controls protein synthesis (makes mRNA)
• nucleolus description


  -area of dense chromatin within the nucleus

  -granular structure (not membrane bound)
• nucleolus function


  -makes ribosomal RNA (rRNA) and makes ribosomes
• rough endoplasmic reticulum description

  -flattened sacs (cisternae)

  -continuous outer nuclear membrane

  -studded with ribosomes
• rough endoplasmic reticulum function

  -ribosomes make proteins which is then transported to the ER's flattened sacs

  -some proteins are secreted by the cell, others are used within the cell
• smooth endoplasmic reticulum description

  -flattened sacs (cisternae)

  -NOT studded with ribosomes
• smooth endoplasmic reticulum function

  -produces lipids
• golgi apparatus description


  -a stack of membrane bound flattened sacs
• golgi apparatus function


  -receives proteins packed in vesicles from ER

  -modifies proteins e.g by the addition of sugars

  -packages modified proteins into vesicles for transportation to the cell surface membrane and secretion out the cell
• ribosome description


  -small

  -not membrane bound

  -consists of two subunits
• ribosome function


  -site of protein synthesis

  -mRNA from the nucleus is read and used to assemble amino acids
• lysosome description


  -spherical sacs surrounded by a single layer of membrane

  -contain powerful digestive enzymes
• lysosome function


  -protects the cell from the enzymes contained within

  -enzymes used in the breakdown of materials
• vesicle description


  -membrane bound sac
• vesicle function


  -used to move substances around cells
• plasma membrane description


  -present in all living cells

  -a selective barrier between the cell's contents and external environments
• plasma membrane function


  -controls the passage of substances into and out of the cell

  -regulates the internal environment of the cell
• mitochondria description


  -spherical sausage-shaped organelle formed from two membranes

  -inner membrane, highly folded to form cristae
• mitochondria function


  -site of aerobic respiration

  -produces adenosine triphosphate (ATP)
• chloroplast description


  -two layers of membrane

  - inner layer is continuous and formed flattened membrane sacs called thylakoids
• chloroplast function


  -site of photosynthesis (a process where glucose is produced)

  -contains a chlorophyll (a photosynthetic pigment)
• cellulose cell wall description


  -on the outside of plant cell's membrane
• cellulose cell wall function

  -supports the cell

  -helps maintain shape
• vacuoles description


  -a large membrane bound sac containing water and solutes
• vacuoles fucntion


  -storage of water and solutes

  -maintains cell turgidity