Staining (microscopy) Flashcards
What is staining?
With coloured/ fluorescent chemicals that bind to cell organelles and makes them visible allows to identify different types of cells and different organelles (providing contrast)
What are stains in microscopy?
Are used to increase the contrast of a sample by selectively binding to certain structures within the sample and changing their optical properties
What is a contrast in biology?
Refers to the degree of visibility or differentiation between different structures or cells within a sample
What would happen without staining?
Many structures within a sample may appear transparent or have similar refractive indices, making it difficult to distinguish between them
How do stains help address this issue?
By making certain structures or cells more visible and thus increasing the contrast
What are simple stains?
- they involve the use of a single dye to colour all of the cells or structures in a sample
- methylene blue can be used to stain DNA
- The stain is positively charged so attracted to the negatively charge DNA. All DNA will stain the same, from bacteria to humans
What can you see in simple stains?
1) the shape
2) some basic structures
3) relative size
What are differential stains?
Uses multiple dyes to distinguish different types of cells or structures based on their physical or chemical properties. The second dye is called a COUNTERSTAIN. Usually it’s a contrasting colour to the principal stain.
What are differential stains used for?
- contrast two cell types
- indicate cell parts (eg gram stain and endospore stain)
What are most stains in microbiology like and what does this involve?
- these involve the use of more than one dye (so that certain differences between cell type and structure can be distinguished)
What is the most important differential stain?
The Gram Stain
Why is staining used when preparing specimens to be examined under a microscope?
- so the cells and their contents are visible
- to increase contrast
- so organelles can be seen eg nucleus
What are the two different gram stain groups?
Gram positive (violet) and Gram negative (red)
What is the gram stain technique for?
It is used to separate bacteria into two groups, Gram positive bacteria and Gram negative bacteria
How is Gram - positive tested?
- Crystal violet is first applied to a bacterial specimen on a slide
- then iodine, which fixes the slide
- the slide is then washed with alcohol
-the gram positive bacteria retains the crystal violet stain and will appear blue/purple under the microscope