Short answers, pulled from the story.
The five basic tastes are sweetness, sourness, saltiness, bitterness, and savoriness, also known by the Japanese term umami. Each is detected by a distinct mechanism: sweetness, savoriness, and bitterness through G protein-coupled receptors, while saltiness and sourness are detected via ion channels.
Umami was first studied in 1907 by Japanese chemist Kikunae Ikeda, who isolated the taste from dashi broth and identified the molecule responsible as monosodium glutamate (MSG). L-glutamate signals the presence of amino acids, which the body uses to build muscles, organs, and enzymes.
There are between 2,000 and 5,000 taste buds located on the back and front of the tongue, with additional taste buds on the roof, sides, and back of the mouth and in the throat. Each taste bud contains 50 to 100 taste receptor cells.
The most bitter substance known is the synthetic chemical denatonium, which has a bitterness index of 1,000 relative to quinine. It was discovered accidentally in 1958 during research on a local anesthetic by T. and H. Smith of Edinburgh, Scotland, and is now used as an aversive agent added to toxic substances to prevent accidental ingestion.
A supertaster is a person whose sense of taste is significantly more sensitive than most people's, likely due in part to an increased number of fungiform papillae. Supertasters experience bitter compounds such as phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP) as intensely bitter, a sensitivity determined by two common alleles at the TAS2R38 locus.
The burning sensation from spicy foods is technically not a taste but a phenomenon called chemesthesis. Compounds such as capsaicin from chili peppers and piperine from black pepper activate TRPV1 and TRPA1 receptors on somatosensory nerve fibers, which register pain and temperature, rather than acting on taste buds at all.