Chapter 9 / 9.7 Structure of Proteins

Understanding Protein Structure 🧬

What Are Proteins Made Of?

Proteins are chains of amino acids linked together like beads on a string! ✨

The 4 Levels of Protein Organization

1. Primary Structure �
   • The exact sequence of amino acids in the chain
   • First amino acid = N-terminal 🆕
   • Last amino acid = C-terminal ©️
   • Like letters forming words!
2. Secondary Structure 🔄
   • Local folding patterns along the chain
   • Right-handed helix (spiral staircase shape)
   • Beta-pleated sheets (zigzag folds)
   • Held by hydrogen bonds 🤝
3. Tertiary Structure 🧶
   • Overall 3D shape of the entire chain
   • Folds like a tangled wool ball
   • Stabilized by disulphide bonds 🔗
   • Essential for protein function!
4. Quaternary Structure 🧩
   • Multiple protein chains assembled together
   • Example: Hemoglobin has 4 subunits
   • Human hemoglobin = 2 α-type + 2 β-type chains
   • Can form cubes, plates, or linear strings

Enzymes – The Special Proteins ⚡

• Most enzymes are proteins 🧪
• Some nucleic acids act as enzymes too (called ribozymes)
• Enzymes have all 3D structures like other proteins

NEET Must-Knows 💡

• Protein structure levels (1° to 4°) – definitions & examples
• Hemoglobin = 4 subunits (2α + 2β) → quaternary structure
• Bonds in folding: Hydrogen bonds (2°), disulphide bonds (3°)
• Enzymes = mostly proteins, but ribozymes are nucleic acids
• Secondary structures: Right-handed helix & beta-pleated sheets