Protein or the physical region of the protein that participates in chemical catalysis. In solution proteins also undergo variation in structure through thermal vibration and the collision with other molecules. Proteins can be informally divided into three main classes, which correlate with typical tertiary structures: globular proteins, fibrous proteins, and membrane proteins. Almost all globular proteins are soluble and many are enzymes. Fibrous proteins are often structural, such as collagen, the major component of connective tissue, or keratin, the protein component of hair and nails. Membrane proteins often serve as receptors or provide channels for polar or charged molecules to pass
Flora and fauna of the Outer Hebrides there occasionally, but are more common off the West Beach. The grey seal now breeds on Hirta but did not do so before the 1930 evacuation. The beach at Village Bay in St Kilda is unusual in that its short stretch of summer sand recedes in winter, exposing the large boulders on which it rests. A survey of the beach in 1953 found only a single resident species, the crustacean isopod "Eurydice pulchra". Amongst the more exotic species found off the Outer Hebrides, is the giant squid ("Architeuthis") - specimens are occasionally washed up on the islands. There are only