Which of the following regarding alpha-helix and beta-sheet is true? The backbone amino group of every amino acid in an a-helix form a covalent bond with backbone carbonyl group of the amino acid four positions away. The amino acid side chains are extended outward from the surface of the alphahelix. For a single-pass transmembrane protein, the amino acids in the transmembrane segment have polar side chains. Hydrogen bonds are not used in the formation of beta-sheet