Which types of bonds or interactions are found in the β-helix of protein?

The correct option is H-bond.

Detailed Explanation:

1. Understanding the β-helix:
A β-helix (beta-helix) is a protein secondary structure created by the association of parallel β-strands winding in a helical manner. This arrangement forms a sturdy, prism-like spiral coil.

2. The Role of Hydrogen Bonds (H-bonds):
The stability and shape of the β-helix are primarily maintained by backbone hydrogen bonds. These H-bonds form between the carbonyl oxygen of a peptide group on one turn and the amide hydrogen of a peptide group on an adjacent turn of the helix.

3. Why the other options are incorrect:
• Ionic bonds are electrostatic attractions between charged side chains that typically stabilize tertiary or quaternary protein structures, rather than driving the secondary structure helical fold.
• Covalent interactions, such as peptide bonds, hold the amino acid chain together but are not the non-covalent interactions that direct and stabilize the folding of secondary structures.
• Banana bonds (bent bonds) are strained covalent bonds found in small ring organic compounds (like cyclopropane) and are completely unrelated to protein structures.