Alpha Helices

Definition

Alpha helices are a common secondary structure found in proteins, where the polypeptide chain coils into a spiral shape stabilized by hydrogen bonds. This structure is crucial for the overall three-dimensional folding and function of many proteins.

5 Must Know Facts For Your Next Test

1. Alpha helices are stabilized by hydrogen bonds formed between the carbonyl oxygen of one amino acid and the amino hydrogen of the amino acid four residues down the polypeptide chain.
2. The amino acids within an alpha helix have a characteristic $\phi$ and $\psi$ dihedral angle, with $\phi$ around -57 degrees and $\psi$ around -47 degrees.
3. Alpha helices are typically 10-20 amino acids in length and have a pitch (the distance the helix advances per turn) of approximately 5.4 Angstroms.
4. The side chains of amino acids in an alpha helix point outward, allowing for interactions with other parts of the protein or with the surrounding environment.
5. Alpha helices are commonly found in globular proteins, where they help to stabilize the overall three-dimensional structure and facilitate important biological functions.

Review Questions

• Describe the structural features that stabilize an alpha helix.
  • Alpha helices are stabilized by the formation of hydrogen bonds between the carbonyl oxygen of one amino acid and the amino hydrogen of the amino acid four residues down the polypeptide chain. This creates a spiral pattern where the side chains of the amino acids point outward, allowing for interactions with other parts of the protein or the surrounding environment. The characteristic $\phi$ and $\psi$ dihedral angles of the amino acids within the helix also contribute to its stability and overall structure.
• Explain the importance of alpha helices in the overall three-dimensional structure and function of proteins.
  • Alpha helices are a crucial secondary structure in proteins, as they help to stabilize the overall three-dimensional folding of the polypeptide chain. The hydrogen bonding and specific dihedral angles within the helix create a rigid, spiral structure that can interact with other secondary structures, such as beta sheets, to form the complex tertiary and quaternary structures of proteins. These higher-order structures are essential for the proper functioning of proteins in biological systems, as they determine the protein's shape, binding interactions, and catalytic activities.
• Analyze how the structural features of alpha helices, such as their length and the orientation of amino acid side chains, contribute to the diverse roles they play in protein function.
  • The structural features of alpha helices, including their typical length of 10-20 amino acids and the outward-pointing orientation of their side chains, allow them to serve a variety of important functions in proteins. The relatively short length and rigid structure of alpha helices makes them well-suited for forming stable, localized regions within larger protein structures, such as binding sites or transmembrane domains. The exposed side chains of the amino acids in the helix can participate in interactions with other parts of the protein, ligands, or the surrounding environment, enabling alpha helices to play crucial roles in catalysis, signal transduction, and other biological processes. The versatility of alpha helices is a key factor in the diverse functions they fulfill within the complex three-dimensional structures of proteins.

Related terms

Secondary Structure:

The local three-dimensional structure of a protein, formed by hydrogen bonding between different parts of the polypeptide chain.

Polypeptide Chain:

The linear sequence of amino acids that makes up a protein, which then folds into a specific three-dimensional structure.

Hydrogen Bonding:

A type of dipole-dipole attraction that occurs between a hydrogen atom covalently bonded to a highly electronegative atom and another highly electronegative atom, stabilizing molecular structures.