Final answer:
Anti-tubulin antibodies cannot label the microtubules inside live cells due to the intact plasma membrane. Cells must be fixed and their membranes permeabilized for antibodies to enter and bind to their targets, enabling the visualization of structures like microtubules with fluorescence microscopy.
Step-by-step explanation:
If you expose live cells to anti-tubulin antibodies, the microtubules inside the cell will not be labeled simply because antibodies cannot penetrate the intact plasma membrane of living cells. Antibodies are large molecules, and the cellular membrane is made to protect the interior of the cell from extracellular molecules, including antibodies. However, to study intracellular structures like microtubules using immunofluorescence microscopy, cells are first fixed with special chemicals and treated with alcohol or other permeabilizing agents. This treatment disrupts the cell membrane, creating pores large enough for antibodies to enter.
In the context of the options provided regarding the purpose of alcohol treatment in enzyme immunoassays (EIA), the correct answer is 'a' because it makes holes in the cell membrane large enough for antibodies to pass.
This procedure allows the tagged antibodies to bind to their specific targets within the cell. In the study of microtubules, fluorescently labeled anti-tubulin antibodies can then bind to the microtubules and, upon irradiation with UV light, will emit fluorescence that can be observed under a fluorescence microscope, enabling researchers to visualize cellular structures. It's important to note that this process is applicable to fixed and permeabilized cells, not live cells with intact membranes.