Question

In the Ouchterlony assay, we see a sharp precipitin arc form between antigen and antiserum. Why does this arc remain visible for a long time?

A.The antibody molecules are too large to diffuse through the agar.
B.The precipitin lattice is too large to diffuse through the agar.
C.Methanol, added once the arc forms, denatures the protein and blocks diffusion.
D.The antigen molecules are chemically coupled to the gel matrix.

Answer 1

The precipitin arc in the Ouchterlony assay remains visible because the antigen-antibody lattice is too large to diffuse through the agar gel, resulting in a stable and easily visible complex.

Step-by-step explanation:

The sharp precipitin arc formed in the Ouchterlony assay between an antigen and antiserum remains visible for a long period because the precipitin lattice that forms at the zone of equivalence is too large to diffuse through the agar gel. As the antigen and antibody diffuse through the gel and meet at this optimal ratio, they form an interconnected network that is stable within the medium.

This complex is visible as a sharp arc and represents a physical manifestation of the antigen-antibody reaction. Unlike smaller molecules, this precipitin lattice is too complex and large to migrate further into the gel, thus it remains intact, allowing for easy visualization of the antigen-antibody interaction, which makes the assay particularly useful for identifying cross-reactivity between different antigens and antibodies.