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Bacteriology > Chapter 2 > Flashcards

Chapter 2 Flashcards

1
Q

Resolution

A
  • is the smallest distance by which two objects can be separated and still be distinguished
  • limits the ability of what we can see with a microscope
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2
Q

Detection

A

is the ability to determine the presence of an object

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3
Q

Magnification

A

is the increase in the apparent size of an image to resolve smaller separations between objects

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4
Q

Microbial Shape

A
  • Prokaryotic cell structures are generally simpler than those of eukaryotes
  • Certain shapes of bacteria are common to many taxonomic groups
  • Bacilli = rods
  • Cocci = spheres
  • Spiral forms = Spirochetes and Spirilla
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5
Q

For electromagnetic radiation to resolve an object, certain conditions must exist

A
  1. Contrast between object and its medium
  2. Wavelength smaller than the object
  3. Magnification
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6
Q

Absorption

A

means that the photon’s energy is acquired by the absorbing object

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7
Q

Reflection

A

means that the wavefront bounces off the surface of an object

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8
Q

Refraction

A

is the bending of light as it enters a substance that slows its speed

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9
Q

Scattering

A

occurs when the wavefront interacts with an object smaller than the wavelength of light

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10
Q

empty magnification

A

magnification without increasing detail is called

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11
Q

compound microscope

A
  • a system of multiple lenses to increase magnification and produce an upright image
  • Basic design contains 2 lenses = Ocular lens and Objective lens
  • Total magnification = magnification of ocular multiplied by that of the objective
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12
Q

wet mount

A

-simple way to observe microbes is to place them in a drop of water on a slide with a coverslip

Advantages:
-Observation of live cells in natural state

Disadvantages:

  • Little contrast between cell and background
  • Sample may dry out quickly
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13
Q

Fixation

A
  • cells are made to adhere to a slide in a fixed position with heat or chemicals
  • usually kills the cells
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14
Q

Staining

A

-cells are given a distinct color with a dye, which produces increased contrast

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15
Q

simple stain

A
  • adds dark color specifically to cells, but not to the external medium or surrounding tissue
  • A commonly used stain is methylene blue
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16
Q

differential stain

A
  • stains one kind of cell but not another

- The most common differential stain is the Gram stain

17
Q

Gram stain

A
  • differentiates between two types of bacteria
  • Gram-positive bacteria retain the crystal violet stain because of their thicker cell wall
  • Gram-negative bacteria do not
18
Q

Acid-fast stain

A

-carbolfuchsin used to stain Mycobacterium species

19
Q

Spore stain

A

malachite green used to detect spores of Bacillus and Clostridium

20
Q

Negative stain

A
  • like india ink
  • leaves a white area around the cells which i the carbohydrate layer
  • carbohydrate layer use to protect the cells from our immune system
  • colors the background, which makes capsules more visible
21
Q

fluorescence microscopy

A
  • fluorescent molecules absorbs light of a defined wavelength, and then fluoresce by emitting light of lower energy, thus longer wavelength
  • Can be used to stain specific cell types in complex samples or specific cellular components
  • Can be used to follow expression of fluorescent reporter proteins such as GFP
22
Q

excitation wavelength

A

specimen absorbs light of a specific wavelength

23
Q

emission wavelength

A

emits light at a longer wavelength

24
Q

filters

A
  • To limit incident light to the wavelength of excitation and emitted light to the wavelength of emission
  • high-intensity light source shines through an excitation filter that transmits only the range of wavelengths to excite the fluorophore
25
Q

fluorophore

A
  • is a fluorescent chemical compound

Its cell specificity can be determined in at least 3 ways:

1) Chemical affinity for a cellular component
2) Labeled antibodies that bind to specific cellular components 3) DNA hybridization to specific DNA sequences

26
Q

Dark-Field Microscopy

A
  • light stop is used to stop light from going directly through the sample to your eye
  • enables microbes to be visualized as bright objects against a dark background
  • Light shines on sample at an oblique angle
  • Only light scattered by the sample reaches objective
  • Makes visible objects below resolution limit
  • Flagella and Very thin bacteria
27
Q

Phase-Contrast Microscopy

A
  • Superimposes refracted light and transmitted light shifted out of phase
  • Reveals differences in refractive index of different cell components as patterns of light and dark resulting from constructive and destructive interference
  • Can be used to view live unstained cells and internal cellular organelles of larger eukaryotic cells
28
Q

Electron Microscopy

A

Electrons behave like light waves

  • Very high frequency, which allows greater resolution
  • A few nanometers
  • Lenses are magnetic fields

Sample must absorb or reflect electrons
-Stained or coated with heavy metals (kills cells)

Electrons are easily affected by matter

  • Electron beam and sample must be in a vacuum (cells must be dehydrated)
  • Samples must be very thin
29
Q

Transmission electron microscopy (TEM)

A
  • Electrons pass through the specimen
  • Reveals internal structures
  • preparation- Embedded in a polymer for thin sections
  • Microtome with a diamond knife is used to cut very thin slices
  • Molecular samples can be sprayed onto a thin film supported by a copper grid
  • closely parallels the design of the bright-field microscope
  • light source is replaced by an electron source consisting of a high-voltage current applied to a tungsten filament, which gives off electrons when heated
30
Q

Scanning electron microscopy (SEM)

A
  • Electrons scan the specimen surface
  • Reveals external features in 3D
  • preparation- specimen is not sliced but is coated with heavy metal
  • scattered and secondary electrons emitted from the sample are detected
  • electron beam is scanned across a specimen coated in gold, which acts as a source of secondary electrons
31
Q

X-ray crystallography

A
  • For samples that can be crystallized, X-ray diffraction can determine the position of individual atoms in a molecule
  • Many organic molecules and proteins can be crystallized, but some do not produce suitable crystals
  • A beam of X-rays is shot at a crystallized sample
  • Many molecules are in identical conformation in the crystal
  • X-rays diffract according to position of atoms
  • Compute position of atoms from pattern of scattered X-ray
  • undergo mathematical analysis to generate molecular models

Bacteriology (16 decks)

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