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
The Head and the Hair in the 18–49 demographic. Liz Lemon (Tina Fey) and Jenna Maroney (Jane Krakowski) keep running into the same two men in the elevator at the 30 Rock building, and find themselves interested in them. Not knowing their names, Liz and Jenna refer to them as "The Head" (Brian McCann) and "The Hair" (Peter Hermann). After talking with Jenna, Liz decides she is going to ask "The Head" out on a date. However, on her way to find him, she runs into "The Hair", who asks her out, and discovers his name is Gray. She agrees to attend a restaurant opening