Noncovalent Interactions (the most important)

These are weak individually, but collectively they control structure, recognition, and function:

• Hydrogen bonds

Form between electronegative atoms (like O or N) and hydrogen.

→ Stabilize DNA base pairing and protein secondary structure (α-helices, β-sheets).

• Ionic interactions (electrostatic forces)

Between charged groups (e.g., COO⁻ and NH₃⁺).

→ Important in enzyme–substrate binding and protein folding.

• Van der Waals forces

Very weak attractions between nearby atoms.

→ Help pack molecules tightly (e.g., protein interiors).

• Hydrophobic interactions

Nonpolar molecules cluster together in water.

→ Drive protein folding and membrane formation.

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2. Covalent Interactions

Stronger and more permanent:

• Peptide bonds → link amino acids in proteins

• Phosphodiester bonds → link nucleotides in DNA/RNA

• Disulfide bonds → stabilize protein structure

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