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Agarose is a neutral polysaccharide extracted
from the cell walls of certain Rhodophyceae
algae, also known as agarophyte seaweeds. Its chemical structure gives agarose
the capacity to form very strong gels even at low concentrations. These gels
have a macroreticular structure with a very open mesh which can be adjusted
simply by varying the concentration of agarose.
The macroreticule of the agarose gel is formed by hydrogen bonds, which makes
the gel thermo-reversible, thus it melts upon heating. The hysteresis –
difference between gelling and melting temperature – is greater than in any
other hydrocolloid. In addition, the absence of ionic groups makes the gel a
neutral structure, thus avoiding interactions with hydrophilic macromolecules
which migrate through the gel mesh.
All applications for agarose take advantage of the special characteristics of
the macroreticular gel. It is used as a sieve or a support through which
biological macromolecules such as proteins or nucleic acids can pass. Larger
particles, such as viruses and subcellular fragments, are also able to move
through the gel network.
• Immunodiffusion: In this technique,
macromolecules migrate and are precipitated in the gel by molecular diffusion.
• Electrophoresis: Agarose is suitable for the
widest range of electrophoretic procedures as well as in immunoelectrophoresis
and electrofocusing. Driven by electrostatic fields, the macromolecules migrate
through the macroreticular structure.
• Gel Chromatography, Affinity Chromatography and Ion
Exchange Chromatography: In these applications, the movement of
macromolecules is caused by the displacement of solvent along the gel formed in
• Solid Culture Media. Solid or semi-solid media
are used to grow plant cells and tissues. Culture media prepared with agarose
(instead of agar) can be used for strict autotrophic bacteria.
• Growth of Protein Crystals. The agarose gel
regulates the diffusion of the protein molecules, allowing the formation of
crystals suitable for crystallographic study.
There are several other scientific and technical applications and new ones are
continously being developed.