EDTA is a chelator of metal cations. In order to detect a 6-His tag, nickel beads are used. If EDTA is in the solution, it will chelate the nickel from the beads and prevent detection of the protein.

When tagging the N-terminus of a protein, the main purpose is to detect this protein by a widely commercial antibody to the tag. Many proteins that researchers intend to study do not have a specific antibody, and therefore, the utilization of a HA or FLAG tag allows easy detection. The tag is not intended to alter the native protein's function nor change its expression level in cells. 

One of the purposes of biochemically tagging a protein is to facilitate its detection. As such, it is important that the tag is expressed only when the protein is expressed. Additionally, the in-frame tag is typically fused to the  or -terminus of the protein to ensure minimal disruption in native protein folding and structure. 

Researchers commonly use FLAG, His, HA and GST tags when biochemically tagging proteins for experiments. Often, these tags are fused in-frame to the -terminus of the protein to minimize disruption of native protein folding. Sodium dodecyl sulfate (SDS) is an anionic detergent, that when applied to proteins, destroys their folded secondary and tertiary structure. SDS is most commonly used in Western blots. 

All of the answer choices are true. Creating fluorescently tagged proteins is a common laboratory practice to visualize subcellular localization of proteins. Fusion proteins are subcloned into expression vectors, therefore, it is important that the expression vector is suitable for expression in the species one wishes to express the protein. Furthermore, to minimize disruption of native protein fold, fluorescent tags are usually added to either the N or C-termini. Finally, to ensure that translation is not disrupted, the fusion must be in-frame with the native protein. 

The correct answer is Northern blot. A Northern blot is used to detect or quantify RNA in a sample to measure gene expression. A biochemically tagged protein can be detected by Western blot using an antibody specific to the tag. Cell culture cells expressing a tagged protein can also be detected using an antibody specific to the tag by indirect immunofluorescence. Tagging a protein with a fluorescent protein allows researchers to track a protein's localization and movement in cells with live cell imaging. Finally, an electrophoretic mobility shift assay (EMSA) detects a protein's ability to bind DNA, but a super shift incubates the protein of interest with an antibody to determine which protein is binding DNA. In this case, a tagged protein can be probed on an EMSA. 

These are all possible methods for generating a labeled DNA probe that is easier to visualize in a heterogeneous sample. In nick translation, DNase is used to nick the DNA of interests, then DNA Polymerase I replaces some nucleotides with their labeled analogues. End labeling involves the use of labeled nucleotides that prevent further elongation at the ends of the DNA molecule. PCR with a radioactive label is another method of cloning labeled DNA.

Ribosomes have relatively small molecular weights in comparison to cell organelles, and relatively large molecular weights in comparison to macromolecules (such as proteins). Several rounds of centrifugation, using slightly different conditions, is a feasible way to isolate intact ribosomes.

SDS-PAGE is an excellent technique for separating denatured proteins based on molecular weight. Western blotting is used to detect the presence specific proteins in a sample. Dialysis is often used in protein purification procedures.

The only answer that will viably pull a protein complex out of a solution is co-immunoprecipitation. Co-immunoprecipitation involves using a large amount of antibody for a specific protein to capture the protein of interest and anything that is associated with it (namely the protein complex). The proteins can then be eluted from the antibody and analyzed.

FRET involves fluorescently labeling two proteins to look for, amongst other possible uses, protein-protein interactions in vivo. Southern blotting is a technique used to separate and identify a specific DNA sequence in a solution. Mass spectrometry can be used to analyze and sequence proteins, but does not directly involve the use of antibodies.

Ethidium bromide intercalates into the hydrophobic interior of the DNA double helix and remains bound through Van der Waals interactions. The binding of ethidium bromide to DNA leads to a conformational shift that increases its fluorescence.