Britannica Sources used in this answer

Why do some bitter and odor molecules need soluble proteins to reach receptor cells?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A pine grosbeak with pink and gray plumage perches on a branch, eating red berries among autumn foliage. — Chemoreception Animals, such as this pine grosbeak, use chemoreception to respond to chemicals that can be tasted and smelled in their environments. Many of these chemicals affect behaviors such as food preference and defense.

In the context of chemoreception, many bitter-tasting and volatile odor molecules are not water-soluble. Because the olfactory receptor cells and taste receptors are covered by a layer of mucus or fluid, these hydrophobic compounds cannot move freely to reach the receptor sites on their own.

To overcome this barrier, these molecules bind to soluble proteins found in the saliva or the mucus of the nasal epithelium. These proteins act as carriers, allowing the otherwise insoluble compounds to be transported through the aqueous environment to the receptor cells. In addition to facilitating transport, these proteins may function as filters that govern which chemicals reach the receptor membrane, thereby influencing the sensitivity of the receptor cells to specific stimuli.1