GRE Subject Test: Biology : Understanding Immunological Stains

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #1 : Understanding Immunological Stains

A certain immunostaining technique initially separates antigens to be identified by electrophoresis, then transfers them to a solid membrane. This process was used as the standard for diagnosis of the presence of human immunodeficiency virus. What process is being described?

Possible Answers:

Immuno-electron microscopy

Western blot

Flow cytometry

ELISA (enzyme-linked immunosorbent assay)

Chemiluminescence

Correct answer:

Western blot

Explanation:

The Western blot test identifies antigens by separating them using electrophoresis on a gel, then transferring to a solid membrane by blotting. The process allows clinicians to establish is a specific protein or set of proteins is present in a sample.

Enzyme-linked immunosorbent assay (ELISA) methodology involves identifying the presence of antigens or antibodies in blood by binding them to enzymes that would result in a color change. In flow cytometry, cells are tagged with an antibody carrying a fluorescent label and passed through a detctor. In immuno-electron microscopy, antibodies are labelled with heavy metals and viewed with an electron microscope. Chemiluminescence is the emission of light as the result of a chemical reaction. Luminol is an example of chemiluminescence. 

Example Question #1 : Understanding Immunological Stains

4',6-diamidino-2-phenylindole, commonly known as DAPI, stains what part of the cell when performing immunohistochemistry?

Possible Answers:

A-T rich DNA

Golgi apparatus

Plasma membrane

Nucleolus

Nuclear envelope

Correct answer:

A-T rich DNA

Explanation:

The correct answer is A-T rich DNA. DAPI is a common fluorescent dye used in immunohistochemistry to stain DNA to indicate the localization of the nucleus within a cell, relative to other structures and regions. When bound to DNA, it absorbs ultraviolet light (358nm) and emits blue light (461nm). 

Example Question #3 : Understanding Immunological Stains

When performing whole-mount specimen immunohistochemistry of golgi markers, why is it necessary to porate cell membranes?

Possible Answers:

Poration promotes attachment of cells to a microscope slide

Poration allows the golgi markers to exit the cell

Poration keeps the cells alive, allowing for live-cell imaging 

None of the other answers

Poration of the membrane allows the antibody to enter the fixed cells

Correct answer:

Poration of the membrane allows the antibody to enter the fixed cells

Explanation:

When performing immunohistochemistry, antibodies are often utilized to detect proteins of interest within the cell. However, in order for antibodies to enter fixed cells, there must be holes (pores) artificially made in the cell membrane. 

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