Question

Which stain will you use to observe the nucleus in the cheek cell?

Answer 1

Hint: Nucleus of a cell contains nucleic acid associated with nucleoproteins. Thus, in order to observe a nucleus of a cell the stain used should impart color to the nucleic acid and/or the nucleoprotein. As nucleic acid is acidic and the nucleoprotein is basic in nature, both acidic and basic dyes can be used to stain a nucleus of a cell.

Complete answer:
Although there are various nuclear stains, Methylene blue is the most commonly used nuclear stain to observe the nucleus in the cheek cells. Methylene blue stain is preferred over other dyes due to its simple protocol, can be used without any mordant, and can be observed and distinguished even under a simple light microscope. Also, cheek cells are stained as fixed cells and methylene blue stains can stain fixed cells easily.
Figure 1: Methylene blue-stained cheek cells under a microscope

Other nuclear stains include:
DAPI a stain that can be used in both live and fixed cells, binds to DNA, and imparts DNA with blue fluorescence color on excitation by UV light.
Hematoxylin is a nuclear stain that imparts blue-violet or brown color to the nucleus in the presence of a mordant.
Hoechst stains are two fluorescent nuclear stains (33258 and 33342) that stain DNA in living cells.
Neutral/Toluylene red is a living cell staining nuclear stain that stains the nucleus red.
Safranin is a nuclear stain used as a counterstain and it can also be used to color collagen yellow.
Nile blue used in living cells to stain nucleus blue.

Additional Information:
Cells have different parts that can absorb stains or react with dyes that impart color to different parts of the cell. Thus, helping in distinguishing different parts of the cells. Some of these dyes include:
Bismarck brown is used to stain live cells as it imparts a yellow color to acid mucins proteins.
Crystal violet used in gram staining, it stains the cell walls purple when combined with mordant.
Rhodamine used in fluorescence microscopy to stain proteins.
Osmium tetroxide used to stain lipids black and can be seen under an optical microscope.
Malachite green used to stain bacteria and spores. It is used as a counterstain to Safranin.
Iodine is used as a starch indicator, as it turns the solution dark blue in the presence of starch in the solution.
Carmine is used to color animal starch or glycogen red.
Coomassie blue often used in gel electrophoresis, stain the protein brilliant blue.
Fuchsin used for staining smooth muscles, collagen and mitochondria in a cell.
Crystal violet used in gram staining, it stains the cell walls purple in the presence of a mordant.
Eosin used as a counterstain to hematoxylin, imparts pink or red color to RBCs, cell membrane, extracellular structures, and cytoplasmic materials.

Note: Methylene blue is a basic dye and has a high affinity to acidic DNA and RNA. It is a simple stain as its positively charged dye easily binds to negatively charged phosphate groups of DNA and RNA. Thus, when a cell is stained with methylene blue both nucleus and cytoplasm of the cell looks blue under a microscope, but the nucleus can be distinguished as the darker stained part due to the high concentration of DNA in the nucleus and low concentration of RNA in the cytoplasm. The blue dots in the cytoplasm is due to the presence of bacteria from the mouth and teeth.