All GRE Subject Test: Biology Resources
Example Question #60 : Lab Techniques
Which of the following stains could be used to identify bacteria?
Acid fast stain
Gram staining is used to distinguish different types of bacteria in order to aid in their identification. Since bacteria are generally transparent, they must be stained before viewing under the microscope. Gram-positive microorganisms stain purple and Gram-negative microorganisms stain red or pink.
Acid fast stain is used to identify the causative agent of tuberculosis. White blood cells are differentiated after being stained with Wright's stain. Giemsa is used to stain blood cells and chromosomes. Tissues are stained with eosin.
Example Question #1 : Understanding Identification Techniques
A student co-immunoprecipitates the NF-kappa B transcription factor that is bound to a protein, which the student cannot identify. What technique would be suitable for identifying this unknown protein?
Electrophoretic mobility shift assay (ESMA)
The correct answer is mass spectrophotometry. Mass spec uses ions to measure the mass-to-charge ratio of the given molecule. This signature ratio can then be compared to other known mass-to-charge ratios of other proteins, allowing for identification of the unknown protein based on similar ratios.
Example Question #2 : Understanding Identification Techniques
A student researcher wants to determine if two proteins physically interact within a cell. What technique is best suitable for this experiment?
Chromatin immunoprecipitation sequencing
Chromatin interaction analysis by paired-end tag sequencing
The correct answer is co-immunoprecipitation. Protein-protein interactions are cross-linked within a cell. Using an antibody to the first protein, this protein (along with any molecules bound to it) is isolated from the cell lysate. Then using a second antibody to the second protein of interest, a western blot is performed to determine if the second antibody was pulled down in the first immunoprecipitation with antibody number 1. Immunoprecipitation involves isolating a particular protein out of a solution. Chromatin immunoprecipitation sequencing involves analysis of interactions between DNA and proteins, and is used to identify the binding sites of proteins associated with DNA. Cross linking is the process by which two polymers are joined, it does not indicate whether two proteins were interacting prior to the procedure. Chromatin interaction analysis by paired-end tag sequencing determines chromatin interaction, not protein interaction.