![]() “pleated,” and these structures are, therefore, often called β-pleated sheets. Involved in hydrogen bonding (Figure 2.7A). Of the α-helix if they are present in large numbers.įorm of secondary structure in which all of the peptide bond components are Or amino acids, such as valine or isoleucine, that branch at the β-carbon (theįirst carbon in the R group, next to the α-carbon) can interfere with formation Finally, amino acids with bulky side chains, such as tryptophan, Large numbers of chargedĪmino acids (for example, glutamate, aspartate, histidine, lysine, andĪrginine) also disrupt the helix by forming ionic bonds or by electrostatically Which interferes with the smooth, helical structure. Amino acids that disrupt an α-helix: Proline disrupts an α-helixīecause its secondary amino group is not geometrically compatible with the In the primary sequence are spatially close together when folded in theģ. Thus, amino acid residues spaced three or four residues apart Amino acids per turn: Each turn of an α-helix containsģ.6 amino acids. Hydrogen bonds are individually weak, but they collectivelyĢ. Last peptide bond components are linked to each other through intrachain Hydrogen bonds extend up and are parallel to the spiral from the carbonylįour residues ahead in the polypeptide. Hydrogens that are part of the polypeptide backbone (see Figure 2.6). Hydrogen bonds: An α-helix is stabilized byĮxtensive hydrogen bonding between the peptide-bond carbonyl oxygens and amide Myoglobin, whose structure is also highly α-helical, is a globular, flexibleġ. Hair and skin, and their rigidity is determined by the number of disulfideīonds between the constituent polypeptide chains. They are a major component of tissues such as The keratins are a family of closely related, fibrous proteins whose structure A very diverse group of proteins contains α-helices. Outward from the central axis to avoid interfering sterically with each other Is a spiral structure, consisting of a tightly packed, coiled polypeptideīackbone core, with the side chains of the component amino acids extending Polypeptide helices are found in nature, but the α-helix is the most common. [Note: TheĬollagen α-chain helix, another example of secondary structure. The α-helix, β-sheet, and β-bend (β-turn) areĮxamples of secondary structures commonly encountered in proteins. These arrangements are termed the secondary Generally forms regular arrangements of amino acids that are located near each Backbone does not assume a random three-dimensional structure but, instead,
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