Lab Quiz 2 Flashcards
What two things are accomplished by staining cells?
greater magnification with better resolution
contrast between cells and background
Define a dye
an organic compound containing chromophore and auxochrome chemical groups attached to a benzene ring
What part of a dye is responsible for the color
chromophore
What part of a dye increases the solubility
auxochrome
Basic dyes bind to ____ charged molecules and acidic dyes bind to ____ charged molecules
basic, negatively
acidic, positively
Why are basic dyes commonly used in bacteriology?
Because surfaces of bacterial cells and basic dyes bind to negative molecules
What’s the difference between trinitrobenzene and picric acid?
tribitrlobenzene has three nitro groups, which are common chromophore groups, but is not considered a dye because it is insoluble in water
picric acid is a trinitrobenzene with an hydroxyl group, an auxochrome group, which makes it soluble, and is considered a dye
What is an organic molecule that has a chromophore group but not an auxochrome group called?
chromogen
What is a simple stain?
a stain that consists of one dye that stains a component of a microbial cell
What does methylene blue bind to?
since it is basic, it binds to acidic constituents
What’s the basic procedure for simple staining?
Use a sterile loop to place a small drop of water on a slide
Add a small amount of culture to the water
Let air dry
Heat fix the sample
Apply several drops of the dye (methylene blue)
Let slide dry
Examine under microscope with immersion oil
What’s the purpose of heat fixing?
it coagulates the protein causing the organism to where to the slide
Approximately how big is a yeast cell?
7 x 15 µm
What is differential staining?
the use of two or more dyes that are used to categorize cells into groups
What dye did we use as a simple stain?
methylene blue
What species did we observe with simple staining?
Saccharomyces cerevisiae
What dye did we use for differential staining?
Gram’s staining solutions
What’s the basic procedure for Gram’s technique?
Use a sterile loop to place a small drop of water on a slide Add a small amount of culture to the water Let air dry Heat fix the sample Apply crystal violet dye solution Let sit for a minute Rinse with water Apply iodine solution Let sit for a minute Rinse with water Apply decolorized drop by drop until runoff is clear Rinse with water Apply safranin counterstain Let sit for 30 seconds Rinse with water Let dry Examine under oil immersion
In Gram staining, what solution is the mordant?
iodine
In Gram staining, what solution is the mordant?
iodine
What is a counterstain?
dye that has a color that contrasts the primary stain
In Gram staining, what solution is the counterstain?
safranin
What color are Gram-positive cells after staining?
purple
What color are Gram-negative cells after staining?
pink/red
