Alpha helix

Definition

An alpha helix is a common structural motif in proteins characterized by a right-handed coil or spiral shape, where the backbone of the polypeptide chain forms hydrogen bonds between every fourth amino acid. This structure is crucial for protein stability and functionality, contributing to the overall secondary structure of proteins, which also includes beta sheets and random coils.

5 Must Know Facts For Your Next Test

1. The alpha helix typically consists of about 3.6 amino acids per turn, allowing for compact and efficient packing within the protein structure.
2. Alanine is one of the amino acids that most favors the formation of an alpha helix due to its ideal side chain properties.
3. The presence of proline can disrupt the formation of an alpha helix because it introduces a kink in the polypeptide chain, making it less flexible.
4. Alpha helices can vary in length and play significant roles in protein-protein interactions and functional sites within enzymes.
5. In many proteins, alpha helices can be found coiled together to form larger structures or bundles that contribute to the protein's overall stability and function.

Review Questions

• How does the structure of an alpha helix contribute to protein stability?
  • The alpha helix contributes to protein stability through the formation of hydrogen bonds between the carbonyl oxygen of one amino acid and the amide hydrogen of another amino acid located four residues earlier in the sequence. This regular pattern of hydrogen bonding helps maintain the helical shape, allowing proteins to remain structurally sound under various conditions. The presence of these bonds minimizes the energy of the protein's folded state, making it more stable.
• Compare and contrast alpha helices with beta sheets in terms of their formation and role in protein structure.
  • Alpha helices and beta sheets are both important components of protein secondary structure, but they differ significantly in their formation. Alpha helices are formed by hydrogen bonds between backbone atoms in a single polypeptide chain, resulting in a right-handed coil. In contrast, beta sheets are formed by hydrogen bonds between backbone atoms in different strands of polypeptide chains, creating a pleated sheet-like structure. While both structures provide stability to proteins, alpha helices are often involved in specific functions like binding sites or signaling, whereas beta sheets provide structural support and can form rigid frameworks.
• Evaluate the importance of alpha helices in enzyme activity and molecular recognition processes.
  • Alpha helices play a crucial role in enzyme activity and molecular recognition by providing specific sites for substrate binding or interaction with other molecules. Their predictable structure allows for precise fitting into active sites where catalysis occurs. Furthermore, many regulatory mechanisms rely on conformational changes involving alpha helices that affect how enzymes interact with substrates or inhibitors. This versatility makes them essential for understanding enzyme kinetics and designing drugs that target specific protein functions.

Related terms

Hydrogen bond: A weak bond that forms between a hydrogen atom, which is covalently bonded to a more electronegative atom, and another electronegative atom. In proteins, hydrogen bonds stabilize the alpha helix structure.

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

Tertiary structure: The overall three-dimensional shape of a single polypeptide chain, formed by the interactions between the side chains of amino acids, including those that arise from secondary structural elements like alpha helices.