Chapter 3 Flashcards
How large is a micron? A nanometer? A picometer? What structures/cells are measured in these units?
Micrometer = 10^-6 m (bacteria to blood cells)
Nanometer = 10^- 9 (Viruses and DNA),
Picometer = 10^-12
How large are prokaryotic cells?
Eukaryotic cells?
Viruses?
1-10 micrometers
10-100 micrometers
10-100 nanometers
With what type of microscopes can you see each of these organisms/structures?
Light microscope 200nm – 10mm , E. coli bacteria up to a tick.
Scanning electron microscope SEM 10nm-1mm Viruses up to most prokaryotic and eukaryotic cells
Transmission electron microscope TEM 10 pm – 100 micrometers, DNA helix up to eukaryotic cells.
Atomic Force Microscope AFM 0.1 nm – 10 nm atomic/molecular processes up to DNA.
What are ocular and objective lenses?
Ocular lens is the eyepiece and the objective lens is the lens closest to the specimen being viewed.
How does one determine total magnification?
Ocular is 10x magnification multiplied by the magnification of the objective. (10x ocular) X (40x objective) = 400x total magnification.
What is resolving power/resolution?
The ability of the lenses to distinguish two points a specified distance apart. If resolving power were 0.4 nm , then two points can be distinguished if they are at least 0.4 nm apart.
• What is the difference between simple and differential stains?
A single basic dye is used to highlight an entire organism. A negative stain uses a simple stain of safranin to identify capsules. Differential stain uses more than one dye to distinguish different kinds of bacteria.
What structures can be visualized with each (what specific examples did we look at and when are they used)?
Gram stains are used to classify bacteria as gram negative or positive based on the traits of their cell wall, will color dark violet for positive and pink for negative. Acid-Fast stains bind strongly to bacteria with waxy material in their cell walls, this is used to identify Mycrobacterium.
What type of microscopy are they used with?
Primarily light microscropy / Koehler illumination.
What are the uses and drawbacks of phase contrast, fluorescence and confocal microscopy?
Phase contrast microscopy: allows viewing of living organisms and they do not need to be fixed. Direct rays of light passing through the specimen are collected along with rays diffracted off the specimen. These rays are combined at the eye.
Fluorescence microscopy: uses ultraviolet light rays to cause naturally fluorescent organisms or organisms treated with fluorochrome dye to fluoresce when viewed. It is useful for highlighting microorganisms or other pathogenic material even within cells or tissues.
Confocal microscopy: uses fluorescence and computer to collect scanned plans of a specimen to produce a three dimensional image. Can be used to monitor concentration of substances in a cell like ATP or calcium ions. How does each work, basically?
How does electron microscopy differ from light microscopy?
Beams of electrons are used instead of light.
What are the differences between SEM and TEM?
In SEM, primary electrons sweep across the specimen and knock electrons from its surface, which are collected for viewing on a screen. Three dimensional external views are provided of the specimen.
In TEM, electrons pass through the specimen and are scattered, internal structures can be seen.
What are the advantages and drawbacks of electron microscopy?
Drawback is the images are always black and white.
What is probe microscopy?
Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM) used a tungsten or diamond probe on the surface of the specimen to provide a detailed three dimensional view, including depressions and groooves. They resolving power is greater than electron microscopes, special preparation of specimen is not needed.
