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Unformatted text preview: -H of
close chain members.
-1- Left: Alpha helix.
a) turn pattern; b)
backbone atoms; c)
R groups and Hbonds. Right: peptide bond • beta pleated sheet: parallel polypeptides form a plate stabilized by H-bond between C=0
and N-H of adjacent chains.
A three-chain beta sheet. Note the H-bonds between the chains that hold them in the "sheet"
random coil • no structure
tertiary • tridimensional structure made by runs of secondary structure elements (helices and sheets).
Can be stabilized by disulfide bonds (-SH + HS- = -S-S-), and by other, non-covalent bonds
(H, ionic, etc)
quaternary separate, two or more, polypeptides come together and form a complex proteins. Stabilized by H,
ionic, hydrophobic, van der Waals, disulfide bonds. -2- • denaturation: certain conditions such as heat, acid or base, urea treatments cause loss of structure. Examples: cooking egg white or meat
• proteins are immensely flexible compounds that can assume virtually any role and shape. They
serve as the machinery and building block for a very large part of the cell structure and functional components.
(*) important point about Asn. The -NH2 group of Asn can ionize only in strong acid. So, Asn is
effectively a "non-charged" amino acid. By contrast, the -NH2 in the R-group of Lysine (Lys) is
mostly charged and ionized under normal, pH neutral conditions (-NH3+). Lys and Arg
(=NH2+) in R-group are basic amino acids. Secondary and tertiary structure of a protein. The secondary structure is evident in the beta sheet
(magenta) and alpha helix (aquamarine). The tertiary structure is evident in the tridimensional
arrangement of the polypeptide, including the 3D position of alpha-helices and beta-sheets. -3- Pease understand this well.
Image by LadyofHat (Mariana Ruiz Villarreal) -4...
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