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Using an electric field, molecules (such as DNA) can be made to move through a gel made of agarose or polyacrylamide. The electric field consists of a negative charge at one end which pushes the molecules through the gel, and a positive charge at the other end that pulls the molecules through the gel.
The negative charge of its phosphate backbone moves the DNA towards the positively charged anode during electrophoresis. However, the migration of DNA molecules in solution, in the absence of a gel matrix, is independent of molecular weight during electrophoresis, i.e. there is no separation by size without a gel matrix. [12]
Acetylation removes the positive charge on the histones, thereby decreasing the interaction of the N termini of histones with the negatively charged phosphate groups of DNA. As a consequence, the condensed chromatin is transformed into a more relaxed structure that is associated with greater levels of gene transcription. This relaxation can be ...
Addition of an acetyl group has a major chemical effect on lysine as it neutralises the positive charge. This reduces electrostatic attraction between the histone and the negatively charged DNA backbone, loosening the chromatin structure; highly acetylated histones form more accessible chromatin and tend to be associated with active transcription.
For example, the positive charge of ethidium bromide can reduce the DNA movement by 15%. [12] Agarose gel electrophoresis can be used to resolve circular DNA with different supercoiling topology. [16] DNA damage due to increased cross-linking will also reduce electrophoretic DNA migration in a dose-dependent way. [17] [18]
The positive charge on a histone is always neutralized upon acetylation, creating euchromatin which increases transcription and expression of the target gene. [16] Lysine residues 9, 14, 18, and 23 of core histone H3 and residues 5, 8, 12, and 16 of H4 are all targeted for acetylation. [17] [18]
The positive charge of the phospholipids allows cationic liposomes to form complexes with negatively charged nucleic acids (DNA, mRNA, and siRNA) through ionic interactions. Upon interacting with nucleic acids, cationic liposomes form clusters of aggregated vesicles. [2]
It will be fully ionized at a normal cellular pH, releasing protons which leave behind negative charges on the phosphate groups. These negative charges protect DNA from breakdown by hydrolysis by repelling nucleophiles which could hydrolyze it. [73]