Secondary structure in proteins

Figure 2.2 The a helix is one of the major elements of secondary structure in proteins. Main-chain N and O atoms ate hydrogen-bonded to each other within a helices, (a) Idealized diagram of the path of the main chain in an a helix. Alpha helices are frequently illustrated in this way. There are 3.6 residues per turn in an a helix, which corresponds to 5.4 A (1.5 A pet residue), (b) The same as (a) but with approximate positions for main-chain atoms and hydrogen bonds Included. The arrow denotes the direction from the N-terminus to the C-termlnus.

Figure 2.5 Schematic illustrations of antiparallel (3 sheets. Beta sheets are the second major element of secondary structure in proteins. The (3 strands are either all antiparallel as in this figure or all parallel or mixed as illustrated in following figures, (a) The extended conformation of a (3 strand. Side chains are shown as purple circles. The orientation of the (3 strand is at right angles to those of (b) and (c). A p strand is schematically illustrated as an arrow, from N to C terminus, (bj Schematic illustration of the hydrogen bond pattern in an antiparallel p sheet. Main-chain NH and O atoms within a p sheet are hydrogen bonded to each other.

Role of the Amino Acid Sequence in Protein Structure Secondary Structure in Protein.s Protein Folding and Tertiary Structure Subunit Interaction.s and Quaternary Structure... 

Alpha helix one form of secondary structure in proteins in which the polypeptide chain forms a helix having 3.6 amino acid residues per turn. 

Beta sheet a form of secondary structure in proteins. 

Secondary structure refers to regularities or repeating features in the conformation of the protein chain s backbone. Four major types of secondary structure in proteins are (1) the alpha (a) helix, formed from a single strand of amino acids (2) the beta (P) sheet, formed from two or more amino acid strands (from either the same chain or from different chains) (3) the beta (P) bend or reverse turn, in a single strand and (4) the collagen helix, composed of three strands of amino acids. 

The P structure is one of the most important secondary structures in proteins. It occurs in about 80% of the soluble globular proteins whose structures have been determined. In many cases almost the entire protein is made up of P structure. Single strands of extended polypeptide chain are sometimes present within globular proteins but more often a chain folds back on itself to form a hairpin loop. A second fold may be added to form an antiparallel "P meander"102 and additional folds to form P sheets. Beta structures are found in silk fibers (Box 2-B) as well as in soluble proteins. 

Analysis of Linkers of Regular Secondary Structures in Proteins... 

Alpha helix. A helical conformation of a polypeptide chain, predominantly right-handed, with maximal intrachain hydrogen bonding of the peptide bonds one of the most common secondary structures in proteins. 

Protein secondary (11°) structure The local three-dimensional spatial arrangement of amino acids close to one another in the primary sequence. a-Helices and P-sheets are the predominant secondary structures in proteins. 

---