Alpha helix

Definition

An alpha helix is a common structural motif in proteins, characterized by a right-handed coil where the amino acid residues are arranged in a helical pattern stabilized by hydrogen bonds. This structure plays a critical role in determining a protein's overall shape and function, and it's essential to understand its formation, stability, and interactions with other structural elements.

5 Must Know Facts For Your Next Test

1. Alpha helices typically contain 3.6 amino acids per turn, which creates a stable helical structure.
2. The stability of an alpha helix is primarily due to hydrogen bonds between the carbonyl oxygen of one amino acid and the amide hydrogen of another, four residues down the chain.
3. Hydrophobic interactions between non-polar side chains can also contribute to the stability of an alpha helix, making it more favorable in certain environments.
4. The presence of proline can disrupt the formation of alpha helices because it introduces kinks into the backbone due to its unique cyclic structure.
5. Alpha helices are often found in functional regions of proteins, such as transmembrane domains or enzyme active sites, highlighting their importance in biological activity.

Review Questions

• How do hydrogen bonds contribute to the stability of an alpha helix, and why are they essential for protein structure?
  • Hydrogen bonds play a crucial role in stabilizing the alpha helix by forming between the carbonyl oxygen of one amino acid and the amide hydrogen of another amino acid four residues away. This bonding pattern creates a strong, repeating structure that helps maintain the helical shape. The stability provided by these hydrogen bonds is essential for protein structure, as it allows for proper folding and functionality, which are vital for biological processes.
• Discuss how hydrophobic interactions influence the formation and stability of alpha helices in proteins.
  • Hydrophobic interactions significantly influence the formation and stability of alpha helices by encouraging non-polar side chains to cluster together within the core of the helix. This clustering reduces exposure to water, leading to a more energetically favorable arrangement. Consequently, proteins often incorporate alpha helices in regions where hydrophobic residues are abundant, reinforcing their structural integrity while also facilitating proper protein folding.
• Evaluate the impact of proline on alpha helix formation and how this affects protein functionality.
  • Proline has a unique cyclic structure that introduces kinks or bends in the polypeptide chain, which can disrupt the regular formation of alpha helices. This disruption affects how proteins fold and ultimately their three-dimensional structure. If an alpha helix is disrupted by proline near an active site or functional region, it may hinder the protein's ability to perform its biological function, demonstrating how amino acid composition directly influences protein activity.

Related terms

Hydrogen bond: A weak bond formed between two molecules due to the attraction between a proton in one molecule and an electronegative atom in another.

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

Tertiary structure: The overall three-dimensional structure of a protein that results from the folding of its secondary structures and interactions among them.