Secondary protein structure 3-pleated sheet

Michael reactions and, 895 Beta-keto ester, 851 alkylation of, 859-860 cyclic, 892-893 decarboxylation of, 857, 860 Michael reactions and. 895 pKd of, 852 synthesis of, 892-893 Beta-lactam antibiotics, 824-825 Beta oxidation pathway, 1133-1137 mechanism of, 1133-1136 Beta-pleated sheet (protein), 1038 molecular model of, 1039 secondary protein structure and, 1038-1039 Betaine, 720 Bextra. structure of, 544 BHA, synthesis of, 629 BHT, synthesis of. 629 Bicycloalkane. 129 Bijvoet. J. M., 299 Bimolecular, 363... 

Although other secondary protein structures play roles in determining the shapes of proteins, the helix and pleated sheet occur most frequently. A discussion of less common secondary structures is beyond the scope of this text. 

The primary stucture of a protein is simply the sequence of amino acids within that protein. These linked amino acids can either curl into an alpha helix or crisscross to form pleated sheets, which are examples of secondary protein structures. The protein chain of amino acids is typically quite long, such that it may have regions of alpha helices and regions of pleated sheets. The larger structure of the protein that includes all the various contours of the whole protein is the tertiary structure. In some instances, two or more tertiary structures will come together to form an even larger complex known as the quaternary structure. 

What kind of bonding stabilizes helical and /3-pleated-sheet secondary protein structures ... 

Two features that affect secondary protein structure (molecular shape) include the rigid, planar geometry and restricted rotation of the peptide bond, and interchain or intrachain hydrogen bonding of the type C=0-H-N. The a helix and the pleated sheet are common protein shapes. 

Secondary protein structures are the local regular and random conformations assumed by sections of the peptide chains found in the structures of peptides and proteins. The main regular conformations found in the secondary structures of proteins are the a-helix, the fl-pleated sheet and the triple helix (Figure 1.8). These and other random conformations are believed to be mainly due to intramolecular hydrogen bonding between different sections of the peptide chain. 

Spider web is composed mostly of fibroin, a protein with pleated-sheet secondary structure. The pleated-sheet arrangement allows for multiple hydrogen bonds between molecules, conferring great strength. 

B. Secondary Protein Structure - Helices and Pleated Sheets... 

Describe the secondary protein structure known as the pleated sheet. Give two examples of materials containing proteins with this structure. 

P-pleated sheet A secondary protein structure in which protein chains are abgned side by side in a sheetlike array held together by hydrogen bonds. 

Describe how hydrogen bonding results in (a) a-helix and (b) j8-pleated-sheet secondary protein structures. 

The secondary structure of a protein is determined by the spatial arrangement of the polypeptide chain. Evidence obtained mainly from X-ray diffraction patterns (Linus Pauling, 1951, and others) has shown that the chain is typically wound into a helix. The helical form is maintained by hydrogen bonds located at spaced intervals, as shown in Fig. 26.8. The entire structure is called the ALPHA-HELIX. Other secondary structures of proteins include pleated sheets and random coils. 

Section 27 19 Two secondary structures of proteins are particularly prominent The pleated sheet is stabilized by hydrogen bonds between N—H and C=0 groups of adjacent chains The a helix is stabilized by hydrogen bonds within a single polypeptide chain... 

Secondary Structure. The silkworm cocoon and spider dragline silks are characterized as an antiparaHel P-pleated sheet wherein the polymer chain axis is parallel to the fiber axis. Other silks are known to form a-hehcal (bees, wasps, ants) or cross- P-sheet (many insects) stmctures. The cross-P-sheets are characterized by a polymer chain axis perpendicular to the fiber axis and a higher serine content. Most silks assume a range of different secondary stmctures during processing from soluble protein in the glands to insoluble spun fibers. 

The secondary structures we have described here are all found commonly in proteins in nature. In fact, it is hard to find proteins that do not contain one or more of these structures. The energetic (mostly H-bond) stabilization afforded by a-helices, /3-pleated sheets, and /3-turns is important to proteins, and they seize the opportunity to form such structures wherever possible. 

Figure 26.6 (a) The /3-pleated sheet secondary structure of proteins is stabilized by hydrogen bonds between parallel or antiparallel chains, (b) The structure of concanavalin A, a protein with extensive regions of antiparallel / sheets, shown as flat ribbons. 

Proteins have four levels of structure. Primary structure describes a protein s amino acid sequence secondary structure describes how segments of the protein chain orient into regular patterns—either a-helix or /3-pleated sheet tertiary structure describes how the entire protein molecule coils into an overall three-dimensional shape and quaternary structure describes how individual protein molecules aggregate into larger structures. 

The essential distinction between the approaches used to formulate and evaluate proteins, compared with conventional low molecular weight drugs, lies in the need to maintain several levels of protein structure and the unique chemical and physical properties that these higher-order structures convey. Proteins are condensation polymers of amino acids, joined by peptide bonds. The levels of protein architecture are typically described in terms of the four orders of structure [23,24] depicted in Fig. 2. The primary structure refers to the sequence of amino acids and the location of any disulfide bonds. Secondary structure is derived from the steric relations of amino acid residues that are close to one another. The alpha-helix and beta-pleated sheet are examples of periodic secondary structure. Tertiary... 

Two common examples are the a-helix and the P-pleated sheet. These shapes are reinforced by hydrogen bonds. An individual protein may contain both types of secondary structures. Some proteins, like collagen, contain neither but have their own more characteristic secondary structures. 

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