Question

part a
which level of protein structure is characterized by twists and turns stabilized by hydrogen bonds?
primary
secondary
tertiary
quaternary
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Explanation:

To determine the protein structure level with twists/turns and H - bonds:

• Primary: Amino acid sequence, no twists/turns.
• Secondary: Has α - helices (twists) and β - sheets (turns - related), stabilized by H - bonds between peptide groups.
• Tertiary: 3D folding of a single polypeptide, stabilized by various bonds (not just H - bonds for structure - defining twists/turns).
• Quaternary: Multiple polypeptide chains, not about single - chain twists/turns.

So the secondary structure matches the description.

Answer:

secondary