Proteins can have hydrogen bonds between every fourth peptide bond, with hydrogen-bond plane parallel to helical axis and side chains perpendicular to helical axis {alpha helix, protein structure}. Big or charged amino acids disrupt alpha helix. Proline stops alpha helix, because it is imino acid and does not make regular peptide bond.
Proteins can have hydrogen bonds between amino-acid chains lying in opposite directions, with side chains perpendicular to hydrogen bonds {beta sheet, protein structure}. Large amino acids interfere with hydrogen bonding and disrupt beta sheets.
The charged amino acids serine, isoleucine, and proline can make amino-acid-chain turn {beta turn, protein structure}. Proline is imino acid and makes irregular peptide bond at different angle.
Proteins {fibrous protein} can be elongated amino-acid chains. Fibrous proteins are for structure.
Proteins {globular protein} can have polar side chains on surface and non-polar side chains inside, with sharp bends at proline, serine, or isoleucine. Most proteins, such as enzymes, are globular.
Proteins {oligomer} can have multiple amino-acid chains.
Amino acid sequence {primary structure} determines protein properties.
Amino-acid-sequence three-dimensional alignment can be irregular, alpha helix, beta sheet, or beta turn {secondary structure} {conformation, protein}. Heat or chemicals can disrupt secondary structure and change protein conformation {denaturation, protein structure}.
Overall amino-acid-chain shape can be globular or fibrous {tertiary structure}.
Protein oligomers can have multiple amino-acid chains {quaternary structure}. Hydrogen bonds hold chains together. Hemoglobin has two "alpha" chains and two "beta" chains.
5-Chemistry-Biochemistry-Protein
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Date Modified: 2022.0225