Dna will move through the gel along the electric current, its direction depending in part of the molecule's charge. in which direction, positive to negative or vice versa, will dna movce in the electric field? why?

Negative to positive electrode

Since DNA is a negatively charged macromolecule.

Explanation:

DNA is a polymer of nucleotide each of which has a phosphate residue, a pentose sugar, and a nitrogenous base. The presence of phosphate residue in the DNA backbone imparts the whole DNA molecule a negative charge.

Since DNA is negatively charged, various DNA fragments are loaded at the negative terminal during the gel electrophoresis to allow their movement towards the positive electrode present at the other extreme end.  

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

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