α-helices

Definition

α-helices are a common secondary structure found in proteins, where the polypeptide chain coils into a right-handed spiral. This structure is stabilized by hydrogen bonds between the carbonyl oxygen of one amino acid and the amino hydrogen of another, creating a stable, spiral-shaped conformation.

5 Must Know Facts For Your Next Test

1. α-helices are one of the most common and stable secondary structures found in proteins, accounting for approximately 30-40% of amino acid residues in globular proteins.
2. The hydrogen bonds in an α-helix are oriented parallel to the axis of the helix, creating a tight, compact structure that is resistant to denaturation.
3. The amino acid sequence of a polypeptide chain plays a crucial role in determining the formation of α-helices, as certain amino acids (such as proline) disrupt the regular coiling pattern.
4. α-helices are often found in the interior of globular proteins, where they help to maintain the overall tertiary structure and stability of the protein.
5. The presence and distribution of α-helices in a protein's structure can provide important clues about its function and interaction with other biomolecules.

Review Questions

• Explain the structural features that stabilize the α-helix conformation in proteins.
  • The α-helix is stabilized by the formation of hydrogen bonds between the carbonyl oxygen of one amino acid and the amino hydrogen of another, creating a spiral-shaped, right-handed coil. These hydrogen bonds, which are oriented parallel to the axis of the helix, help to maintain the tight, compact structure of the α-helix. Additionally, the regular pattern of the polypeptide chain, with each amino acid residue occupying a specific position within the helix, contributes to the stability of this secondary structure.
• Describe the relationship between the amino acid sequence and the formation of α-helices in proteins.
  • The amino acid sequence of a polypeptide chain plays a crucial role in determining the formation of α-helices. Certain amino acids, such as proline, disrupt the regular coiling pattern of the α-helix due to their unique structural features. The presence of proline, for example, introduces a kink or bend in the polypeptide chain, which can prevent the formation of a continuous α-helix. Conversely, amino acids with small, uncharged side chains (e.g., alanine, glycine, serine) are more likely to facilitate the formation of α-helices, as they can be accommodated within the tight, compact structure without causing significant disruptions.
• Analyze the functional significance of α-helices in the overall structure and stability of proteins.
  • α-Helices play a crucial role in the tertiary structure and stability of proteins. Due to their compact, spiral-shaped conformation and the network of hydrogen bonds that stabilize this structure, α-helices are often found in the interior of globular proteins, where they help to maintain the overall three-dimensional shape and integrity of the protein. The presence and distribution of α-helices can provide important clues about a protein's function and its interactions with other biomolecules. For example, α-helices may be involved in the formation of binding sites or contribute to the structural features that allow a protein to recognize and bind to its specific substrates or ligands. Additionally, the stability of α-helices can help protect the protein from denaturation, making them an important structural element in the maintenance of a protein's native conformation and biological activity.

Related terms

Polypeptide Chain: The linear sequence of amino acids that make up a protein molecule.

Hydrogen Bonds: Attractive interactions between a hydrogen atom covalently bonded to an electronegative atom (such as oxygen or nitrogen) and another electronegative atom.

Secondary Structure: The local, regular three-dimensional structure of segments of a protein molecule, such as α-helices and β-sheets.