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Micro > Chapter 3 > Flashcards

Chapter 3 Flashcards

1
Q

Units of measurement

A

-meter(m) = 100 centimeters (cm)= 1000 millimeters (mm)

  • meter (m) = about 30 inches
  • centimeter (cm)= 1/100m
  • millimeter (mm)= 1/1000m
  • micrometer(um)= 1,000,000m
  • nanometer (nm)= 1/1,000,000,000m

-1m=1000mm=1,000,000

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2
Q

Microscopy: The instruments

A
  • a simple microscope has only one lens
  • compound microscope- the specimen image from the objective lens is magnified again by the ocular lens
  • total magnification= objective lens x ocular lens
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3
Q

Brightfield Microscope

A
  • a compound microscope that shows the specimen against a bright or “white” background
  • background is bight; specimen is dark
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4
Q

Microscopy: Resolution

A

limiting factor in using a microscope is the resolution

  • resolution- the ability of the lenses to distinguish two points as separate
  • the theoretical best resolution for a light microscope is 0.2 um
  • this means that objects smaller than 0.2 um cannot be seen as separate structures
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5
Q

Darkfield

A

background field is dark; the specimen appears bright

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6
Q

phase contrast

A

lens change the light path so that internal structures of the cells are easier to see

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7
Q

Fluorescence

A

-UV light shines on specimen and fluorescent components give of a fluorescent glow

  • Uses UV light
  • fluorescent substances absorb UV light and emit visible light
  • cells may be stained with fluorescent dyes
  • fluorescent dyes are mist often used to make cells visible
    • fluorochromes- fluorescent dyes
    • Auramine O is a flurochrome dye that is absorbed by Mycobacterium tuberculosis (causes TB). When the dye is applied to a specimen that contains the bacteria, the bacteria glow yellow under the fluorescent microscope
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8
Q

relative to size

A

unaided eye- human height, length of nerve/muscle cells, chicken egg and frog egg

light microscope- frog eggs, eukaryotic cells, nucleus, most bacteria and mitochondrion

electron microscope- eukaryotic cells, nucleus, most bacteria, mitochondrion, mycoplasmas, viruses, ribosomes, viroids, prion, proteins, lipids, small molecules and atoms(?)

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9
Q

Fluorescent antibody technique

A
  • used to identify specific types of bacteria under the microscope
  • Antibodies (AB) are highly specific molecules made by the immune system of animals when the animals are exposed to a compound. They react only with that compound
  • In this technique, AB are prepared against specific bacteria, e.g Treponema pallidum, which causes syphilis
  • The AB are attached to a fluorescent dye
  • Ab-dye complex is added that with the specimen
  • if the specimen has Treponema pallidum, the Ab-dye complex sticks
  • under the microscope the cells glow where the dye has attached
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10
Q

electron microscopy

A 
-uses electrons instead of light
the shorter wavelength of electrons gives greater resolution 
2 common types:
1. scanning electron microscopy
2. transmission electron microscopy
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11
Q

Scanning Electron Microscopy (SEM)

A
  • study surface structures
  • an electron gun produces a beam of electrons that scans the surface of a whole specimen
  • secondary electrons emitted from the specimen produce the image
  • 1,000-10,000 magnification
  • resolution 20nm
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12
Q

Transmission Electron Microscopy (TEM)

A
  • study internal structures
  • ultra thin sections of specimens
  • electrons pass through specimen
  • image produced on fluorescent screen and photographed
  • 10,000-100,000 magnification
  • resolution 2.5 nm
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13
Q

preparation of slides for brightfield microscopy

A

-prepare the smear0 the smear is thin film of a solution of microbes on a slide

-clean the glass slide
apply a thin film of the specimen or bacterial culture
-air dry
-heat fix- use a Bunsen burner or Bacti-incinerator to heat the slide
-kills the microbes for safe handling
- causes cells to stick to the slide
-cool before staining

  • Live or unstained cells have little contrast with surrounding medium
  • most bacteria and fungi are stained with dyes to make them more visible under the microscope
  • colored part of dye is called chromophore
    • basic dyes- chromophore has a positive charge
    • acidic dyes- chromophore has a negative charge
  • type of dye used depends on the type of stain
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14
Q

Simple stains

A
  • used of a single basic dye

- examples: methylene blue stain

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15
Q

Differential stain

A
  • uses more than one dye
  • cells stain one color or another depending on the characteristics of their cell wall
  • examples- cram stain, acid-fast stain
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16
Q

Special stains

A
  • usually used to check if a cell has a certain type of structure
  • spore stain (endospore stain)
  • Capsule stain
  • flagella
17
Q

Differential Stains: Gram Stain

A
  • the gram stain classifies bacteria into gram-positive or gram-negative
  • difference is based on the cell wall composition of the cells
  • knowing the gram reaction of the cells will tell you some general characteristics of the cells, example:
    • gram-positive bacteria tend to be killed by penicillin and detergents
    • gram-negative bacteria are more resistant to antibiotics
  • all cells from a species will have the same Gram reaction
18
Q

Differential stains: Gram Stain Procedure

A
  1. heat fix the smear and allow to cool
  2. add crystal violet, stain for 1 minute, rinse with water
  3. add grams iodine a mordant that enhances staining of crystal violet
  4. decolorize with 95% ethanol for 10-15 seconds, rinse with water
  5. apply safranin, a counterstain, rinse after 1min
  6. air dry
  7. view under microscope
19
Q

Differential Stains: Gram Stain Results

A
  • gram positive bacteria have thicker peptidoglycan layer in the cell wall and retain the deep-purple crystal violet dye
  • gram negative bacteria do not retain the crystal violet dye; they appear pink because of the safranin dye
  • always try to use a young culture for accurate results
20
Q

Differential Stain: Acid- Fast Stain

A
  • some cells contain lipids in their cell walls and do not stain well with the Gram stain
  • this high lipid content is characteristic of certain species of bacteria and is used to help identify them
  • the Acid Fast stain will stain these lipid-containing cells
    • acid-fast bacteria stain red
    • nonacid- fast bacteria stain blue
  • important examples-
    • Mycobacterium tuberculosis- human TB
    • Mycobacterium bovis- cattle and human TB
    • Mycobacterium leprae- leprosy
21
Q

Negative stain (special stain)

A

used to detect capsules

22
Q

spore stain (endospore stain) (special stain)

A

used to detect spore-forming cells

23
Q

flagella stain (special stain)

A

visualizes bacterial flagella which cannot normally be seen under the light microscope

Micro (18 decks)

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