Alpha helix, structure

Based on structural properties alone, which of the following compounds is most likely to interrupt alpha-helix structures found in myoglobin ... 

Figure 3-1. a. Alpha-helix structure for a polypeptide or protein b. Pleated sheet structures, depicting parallel (1) and antiparallel (2) variants (Elias 1997, reprinted courtesy ofWiley-VCH.). 

Figure 36.4. Alpha helix structure proposed by Pauling for -kcraiin. Makes room for large side chains. Right-handed helix with 3.6 residues per turn hydrogen bonding within a chain.

In hair, horn, muscle, fingernail, and porcupine quill there are very long protein molecules with the alpha-helix structure extending in the fiber direction (along the length of a hair, sideways in a fingernail). They are not exactly parallel to one another, but are twisted around one another to form ropes of three or seven alpha helixes. 

Determinations of some of these parameters makes it possible to calculate at least a semi-quantitative measure of alpha helix structure in proteins and polypeptides (52). The alpha helix content for the cellulase was found to be about 30%. 

Rowland LP, Shneider NA (2001) Amyotrophic lateral sclerosis. N Engl J Med 344 1688-1700 Sadqi M, Hernandez F, Pan U, Perez M, Schaeberle MD, Avila J, Munoz V (2002) Alpha-helix structure in Alzheimer s disease aggregates of tau-protein. Biochemistry 41 7150-7155 Sanchez de Groot N, Pallares 1, Aviles FX, Vendrell J, Ventura S (2005) Prediction of hot spots of aggregation in disease-linked polypeptides. BMC Struct Biol 5 18 Sasaki T, Kaiser ET (1989) HeUchrome synthesis and enzymic activity of a designed hemeprotein. J Am ChemSoc 111 380-381... 

Alpha farnesene, structure of, 207 Alpha helix (protein), 1038 Alpha-keratin, molecular model of, 1039... 

Johansson, J., Szyperski, T, Curstedt, T., and Wuthrich, K. The NMR structure of the pulmonary surfactant-associated polypeptide SP-C in an apolar solvent contains a valyl-rich alpha-helix. Biochemistry 1994, 33, 6015-6023. 

Segrest MP et al The amphipathic alpha-helix A multifunctional structural motif in plasma lipoproteins. Adv Protein Chem... 

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... 

Figure 11.4 The structural hierarchy in proteins, (a) A segment of primary structure (b) secondary structure illustrated as a segment of alpha helix (c) tertiary structure in which helices are interspersed with coils, and (d) quaternary structure. (Illustration, Irving Geis/Geis Archive Trust. Copyright Howard Hughes Medical Institute. Reproduced with permission.)...

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. 

Secondary structure those protein structures that result from hydrogen bond formation between the amino and carbonyl groups of peptide bonds. The most important ones are the alpha helix and beta sheets. 

The alpha helix and beta sheets are two types of secondary structures exhibited by polypeptides and proteins. (Rae Dejur)... 

The secondary structure of the plasminogen molecule, as determined by circular dichroism spectra, is 80% random coil, 20% beta-structure, and 0% alpha-helix. Electron microscopy has demonstrated the tertiary structure of plasminogen to be a 22- to 24-nm long spiral filament with a diameter of 2.2 to 2.4 nm. 

The structure of proteins determines their function and can be described on four levels, illustrated on page 447. The primary structure is the sequence of amino acids in the polypeptide chain. The secondary structure describes how various short portions of a chain are either wrapped into a coil called an alpha helix or folded into a thin pleated sheet. The tertiary structure is the way in which an entire polypeptide chain may either twist into a long fiber or bend into a globular clump. The quaternary structure describes how separate proteins may join to form one larger complex. Each level of structure is determined by the level before it, which means that ultimately it is the sequence of amino acids that creates the overall protein shape. Fhis final shape is maintained both by chemical bonds and by weaker molecular attractions between amino acid side groups. 

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