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Micro > 2) Observing The Microbial Cell > Flashcards

2) Observing The Microbial Cell Flashcards

1
Q

Resolution

A

the smallest distance by which two objects can be separated and still be distinguished

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2
Q

Which part of the human eye can the finest resolution of two separate point be perceived

A

Fovea

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3
Q

Fovea

A

The portion of the retina where the photoreceptors are packed at the highest density

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4
Q

Detection

A

The ability to determine the presence of an object

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5
Q

Magnification

A

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

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6
Q

Eukaryotic Microbes

A

Protozoa, algae, fungi

10 - 100 um

Can be seen under a light microscope

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7
Q

Prokaryotes

A

Bacteria, archaea

0.4 - 10 um

Subcellular structures too small to resolve by light microscopy

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8
Q

Wavelength of Visible Light

A

400 - 750 nm

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9
Q

For electromagnetic radiation to resolve an object 3 conditions must exist

A

1) Contrast between object and its medium
2) Wavelength smaller than the object
3) Magnification

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10
Q

Absorption means

A

The photon’s energy is acquired by the absorbing object

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11
Q

Reflection means

A

That the wavefront bounces off the surface of an object

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12
Q

Refraction means

A

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

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13
Q

Scattering occurs

A

When the wavefront interacts with an object smaller than the wavelength of light

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14
Q

Magnification requires the

A

Bending of light rays (refraction)

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15
Q

How does refraction accomplish magnification

A

Refraction magnifies an image when light passes through a refractive material shaped so as to spread its rays

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16
Q

Bright-Field Microscopy

A

Generates a dark image of an object over a light background

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17
Q

To increase resolution

A
  • Use shorter wavelength light
  • Reduce contrast
  • Use immersion oil
  • Use wider lens closer to specimen
  • Higher numerical aperture (NA)
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18
Q

Compound microscope

A

A system of multiple lenses designed to correct or compensate for aberration

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19
Q

Total magnification

A

Magnification of the ocular multiplied by that of the objective

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20
Q

Wet mount

A

Placing a drop of water on a slide with coverslip

Advantages - Observation of cells in natural state

Disadvantages - Little contrast between cell and background
- Sample may dry out quickly

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21
Q

Fixation

A

Cells are made to adhere to a slide in a fixed position

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22
Q

Staining

A
  • Cells are given a distinct color
  • Most stains have conjugated double bonds or aromatic rings, as well as one or more positive charges
23
Q

The detection and resolution of cells under a microscope are enhanced by

A

Fixation and Staining

24
Q

Different kinds of stains

A

Simple stain and differential stain

25
Q

Simple Stain

A

Adds dark color specifically to cells, but not to the external medium or surrounding tissue
(Methylene blue is the most commonly used stain)

26
Q

Differential Stain

A

Stains one kind of cell but not another
(Most famous differential stain is the Gram stain)

27
Q

Gram Stain devised

A

In 1884 by Hans Christian Gram

28
Q

Gram-positive bacteria
Gram-negative bacteria

A
  • retain the crystal violet stain because of their thicker cell wall
  • bacteria do not
29
Q

Fluorescence microscopy

A

The specimen absorb light of a defined wavelength and then emits light of lower energy, thus the longer wavelength

30
Q

Excitation wavelength

A

The specimen absorbs light of a specific wavelength

31
Q

Emission wavelength

A

Emits light at a longer wavelength

32
Q

First to demonstrate the possibly of single-molecule tracking of fluorescent proteins in bacteria

A

William Moerner

33
Q

Dark-field Microscopy

A

Enables microbes to be visualized as halos of bright light against darkness

34
Q

Phase-contract microscopy (PCM)

A

Exploits difference in refractive index between the cytoplasm and the surrounding medium or between different organelles

35
Q

Differential Interference Contrast Microscopy (DIC)

A

Enhances contrast by superimposing an image of the specimen onto a second beam of light that generates interference fringes

36
Q

Electron microscopy (EM)

A

The foremost tool for observing the shapes of macro molecular structures

37
Q

Scanning probe microscopy

A

Images the contours of live bacteria

38
Q

X-ray crystallography

A

The tool of choice for atom-level detail of a macromolecule

39
Q

Two major types of electron microscopy

A

Transmission Electron Microscopy (TEM)
Scanning Electron Microscopy (SEM)

40
Q

Transmission Electron Microscopy

A
  • Electrons pass through the specimen
  • Reveals internal structures
41
Q

Scanning Electron Microscopy (SEM)

A
  • Electrons scan the specimen surface
  • Reveals external features in 3D
42
Q

Cryo-electron microscopy (cryo-EM)

A

High-strength electron beams now permit low-temperature

-Specimen does not require staining
- Specimen must be flash-frozen

43
Q

Scanning probe microscopy (SPM)

A

Enables nanoscale observation of cell surfaces

44
Q

Atomic force microscope (AFM)
(example if an SPM)

A
  • It measures the van der Waals forces between electron shells of adjacent atoms of the cell surface and the sharp tip
  • It can be used to observe live bacteria in water or exposed to air
45
Q

Bright-field:
Fluorescence:
Dark-field:
Phase-contrast:

A
  • employs various stains
  • employs fluorophores for labeling
  • detects unresolved objects
  • exploits differences in refractive indices
46
Q

TEM: provides
SEM: provides

A
  • Internal details in 2D
  • External details in 3D
47
Q

Scanning probe microscopes (SPMs) include the atomic force microscope (AFM)

A
  • Allow observation of living cells in water or in air
48
Q

Molecules can be visualized by

A

X-ray crystallography

49
Q

Which of the microscopes allows the best view of bacterial flagella during motility

A

Dark-field microscope

50
Q

Wavelength is the

A

Distance between one peak of a wave and the peak

51
Q

The height of each peak (or depth)

A

Amplitude

52
Q

Frequency of the wave

A

The rate of vibration of the wave or the number of wavelengths within a specified time period

53
Q

The variety of staining techniques (used for light microscopy)

A

Gram staining, acid-fast staining, capsule staining, endospores staining and flagella staining

54
Q

Commonly used light microscopes

A

Brightfield, darkfield, phase-contrast, differential interference contrasts fluorescence, confocal and two-photon microscopes

Micro (1 decks)

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