Final answer:
In a leucine zipper, leucines appear every 7 residues, which corresponds to two full turns of the helix. This pattern is important for protein-protein interactions and structural stability.
Step-by-step explanation:
The subject of the question is Biology and the specific topic is protein structure.
In the context of a leucine zipper, leucines appear every 7 amino acid residues, which corresponds to two full turns of the helix. This pattern is important for the formation of protein-protein interactions and plays a role in the structural stability and function of the protein.
For example, a possible helix could start with the abbreviation 'L' for leucine at position 1 and end with the abbreviation 'Q' for glutamine at position 7. This helix would have a total of 7 amino acid residues.
The leucine zipper is a motif in the α-helix of certain proteins where leucine residues appear every 7th position, projecting from one side of the helix. This periodicity fits with the structure of the α-helix, which has 3.6 amino acid residues per turn.
Thus, the leucines are spaced at approximately two turns of the helix, benefiting protein-DNA binding and dimerization through their hydrophobic side chains. In a larger context, the α-helical segment's secondary structure is composed of right-handed coils stabilized by hydrogen bonds. α-helices and β-pleated sheets are frequent structures found in globular and fibrous proteins, essential for maintaining protein integrity through their resistance against stretching.