Alpha helix

Definition

An alpha helix is a common structural motif in proteins, characterized by a right-handed coil formed by hydrogen bonding between the backbone amide and carbonyl groups. This structure plays a critical role in the overall shape and stability of proteins, influencing their biological functions and interactions.

5 Must Know Facts For Your Next Test

1. The alpha helix is typically about 10-12 amino acids long and each turn of the helix includes approximately 3.6 residues.
2. Hydrogen bonds in an alpha helix occur between the carbonyl oxygen of one amino acid and the amide hydrogen of another amino acid four residues earlier in the sequence.
3. The presence of certain amino acids, like proline, can disrupt the formation of alpha helices due to steric hindrance.
4. Alpha helices are often found in regions of proteins that span membranes, contributing to the stability and functionality of membrane proteins.
5. In many globular proteins, alpha helices play a key role in forming functional domains and facilitating protein-protein interactions.

Review Questions

• How do hydrogen bonds contribute to the stability of the alpha helix structure in proteins?
  • Hydrogen bonds are crucial for stabilizing the alpha helix structure in proteins. These bonds form between the carbonyl oxygen of one amino acid and the amide hydrogen of another amino acid located four residues earlier in the sequence. This specific pattern of bonding results in a helical shape that provides structural integrity, allowing proteins to maintain their functional conformation during various biological processes.
• Discuss how the presence of certain amino acids can affect the formation of alpha helices in protein structures.
  • Certain amino acids can significantly impact the formation of alpha helices due to their unique side chain properties. For instance, proline introduces kinks and rigidity into the polypeptide chain because it lacks a free amide hydrogen needed for hydrogen bonding. Similarly, bulky side chains from other amino acids can create steric clashes that hinder helical formation. Understanding these effects helps explain why some regions of proteins are more prone to adopt helical conformations while others are not.
• Evaluate the role of alpha helices in membrane proteins and how they influence their function within cellular membranes.
  • Alpha helices play a vital role in membrane proteins, where they often contribute to the formation of transmembrane domains. These helices can span lipid bilayers due to their amphipathic nature, with hydrophobic residues facing the lipid environment while polar or charged residues interact with the aqueous environment. This structural arrangement is essential for many functions such as transport, signaling, and enzymatic activity within membranes. The proper folding and arrangement of alpha helices within these proteins are critical for their functionality and interaction with other cellular components.

Related terms

Beta sheet: A secondary structure in proteins formed by hydrogen bonds between adjacent strands, creating a sheet-like arrangement that can be parallel or antiparallel.

Secondary structure: The local folding of the polypeptide chain into structures such as alpha helices and beta sheets, stabilized by hydrogen bonds.

Protein folding: The process by which a protein assumes its functional three-dimensional shape from its linear amino acid sequence, driven by various interactions including hydrophobic effects and hydrogen bonding.