A sulphated galactan from the red seaweeds (Gelidium spp.).
The major gel forming component agarose consisting of a linear chain of sequences of (1,3) linked β -D-galactopyranosyl units and (1,4 ) linkages to 3,6-anhydro-α-D-galactopyranosyl units. Gelation is via the formation of double helices as shown below.
Agar is primarily used as a plating gel for microbial cultures.