The centriole is composed of nine evenly spaced perpheral fibrils of tubulin protein. Each fibril is a triplet. These triplets are arranged in a circle around a central hub that is proteineceous in nature.The hub is connected to the tubules by radial spokes made of protein.
Receptor molecules are specific proteins in the cell's plasma membrane that receive chemical signals from outside the cell. When such chemical signals bind to a receptor, they cause some form of cellular response.