Cue Column | Notes Column
What is the primary structure of a protein? | Linear sequence of amino acids joined by PEPTIDE BONDS (covalent). Example: Insulin
What stabilizes secondary structure? | HYDROGEN BONDS between backbone C=O and N–H groups. Forms alpha-helix (Keratin) or beta-pleated sheet (Silk fibroin)
What stabilizes tertiary structure? | Disulphide bonds (–S–S–, covalent), hydrophobic interactions, ionic bonds, and H-bonds between R-groups. Example: Myoglobin
What is quaternary structure? | Association of 2 or more polypeptide subunits. Example: Haemoglobin (4 subunits: 2α + 2β). Stabilized by same forces as tertiary
How many amino acids exist? | 20 different amino acids. Each has: alpha-carbon + group + COOH group + H + variable R-group
How is a peptide bond formed? | Dehydration synthesis between COOH of one amino acid and of the next. Releases one water molecule per bond. n amino acids → (n-1) peptide bonds
Summary Box
| Level | Stabilizing Bond | Example |
|---|---|---|
| Primary | Peptide bonds (covalent) | Insulin |
| Secondary | Hydrogen bonds (backbone) | Keratin (α-helix), Silk (β-sheet) |
| Tertiary | Disulphide, hydrophobic, ionic, H-bonds (R-groups) | Myoglobin |
| Quaternary | Same as tertiary + subunit interactions | Haemoglobin (4 subunits) |
NEET Trap Alert
Peptide bonds stabilize PRIMARY structure only — NOT secondary or tertiary. Secondary structure is H-bonds of the BACKBONE, not R-groups. Disulphide bonds are at the TERTIARY level (not secondary).