Alpha Helices

Definition

Alpha helices are a common secondary structure of proteins, where the polypeptide chain coils into a spiral-like shape held together by hydrogen bonds. This structural arrangement is crucial for the proper folding and function of many proteins essential to human physiology and health.

5 Must Know Facts For Your Next Test

1. 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 ahead in the polypeptide chain.
2. The amino acids within an alpha helix are arranged in a repeating pattern, with the side chains pointing outward from the central axis of the helix.
3. Alpha helices are often found in the interior of globular proteins, where they help maintain the protein's overall structure and stability.
4. The presence of certain amino acids, such as proline, can disrupt the formation of alpha helices, leading to bends or kinks in the polypeptide chain.
5. Alpha helices are crucial for the function of many proteins, including enzymes, receptors, and structural proteins, as they help to position key amino acid residues for catalysis, ligand binding, or structural support.

Review Questions

• Explain the role of hydrogen bonds in stabilizing the alpha helix structure of proteins.
  • The alpha helix is 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 ahead in the polypeptide chain. These intramolecular hydrogen bonds help to hold the polypeptide chain in the characteristic spiral shape of the alpha helix, providing structural stability and allowing the protein to maintain its functional 3D conformation.
• Describe how the presence of certain amino acids can disrupt the formation of alpha helices in proteins.
  • The amino acid proline, due to its unique cyclic structure, is known to disrupt the formation of alpha helices. Proline's rigid ring structure and lack of a hydrogen atom on the nitrogen atom prevents it from participating in the hydrogen bonding network that stabilizes the alpha helix. The incorporation of proline in the polypeptide chain can lead to bends or kinks in the alpha helix, altering the overall protein structure and potentially affecting its function.
• Analyze the importance of alpha helices for the function of various proteins essential to human physiology and health.
  • Alpha helices are crucial structural elements found in many proteins that are vital for human health and functioning. The stabilizing effect of the hydrogen-bonded alpha helix allows proteins to adopt specific 3D conformations necessary for their biological roles, such as enzymatic catalysis, ligand binding, and structural support. For example, alpha helices are found in the active sites of enzymes, where they position key amino acid residues for efficient substrate binding and conversion. They are also prevalent in receptor proteins, where the helical structures facilitate ligand recognition and signal transduction. Furthermore, alpha helices contribute to the structural integrity of important structural proteins, such as those found in the cytoskeleton and extracellular matrix. The ubiquity of alpha helices in proteins essential to human physiology underscores their critical importance for maintaining proper biological function and overall health.

Related terms

Polypeptide Chain: A long, unbranched polymer composed of amino acids linked together by peptide bonds.

Hydrogen Bonds: Weak attractive interactions between a hydrogen atom attached to a highly electronegative element (such as nitrogen or oxygen) and another highly electronegative element.

Protein Folding: The process by which a protein structure assumes its functional 3D shape from a linear polypeptide chain.