Gel matrices in molecular biology: Agarose, widely used for electrophoresis, is composed of repeating disaccharide units known as what?

Introduction / Context:
Agarose gels are standard for separating nucleic acids based on size. Understanding their chemical composition helps explain pore size, gel strength, and the behavior of DNA/RNA during electrophoresis.

Given Data / Assumptions:

• Agarose is purified from agar (a mixture of agarose and agaropectin) derived from red algae.
• The fundamental repeating unit in agarose is a disaccharide.
• Electrophoretic properties depend on the polymeric network built from these units.

Concept / Approach:
Agarobiose is the repeating disaccharide consisting of alternating 1,3-linked β-D-galactose and 1,4-linked 3,6-anhydro-α-L-galactose. These units polymerize to form agarose chains that create a three-dimensional matrix upon cooling, defining gel porosity used to resolve nucleic acids.

Step-by-Step Solution:

Verification / Alternative check:
Manufacturers specify agarose composition and gelling mechanisms consistent with agarobiose repeats, confirming the structural basis.

Why Other Options Are Wrong:

• Maltose, cellobiose, lactobiose: other disaccharides unrelated to agarose structure.
• “Agar” is the crude mixture, not the repeating disaccharide.

Common Pitfalls:
Confusing agar (mixture) with agarose (purified polymer). Only agarose forms low-charge, low-sulfate gels optimal for DNA electrophoresis.

Final Answer:
Agarobiose