Proteins contain the following chemical linkages in addition to `-CO-NH-` linkages

Options

A. `NH----O=C`
B. `-HS=SH-`
C. `C=N....H-O-`
D. `-O-O-`

Answer

### Step-by-Step Solution:

1. **Understanding Proteins**:
- Proteins are macromolecules made up of long chains of amino acids.
- Each amino acid is linked to another through specific chemical bonds.

2. **Identifying the Primary Linkage**:
- The primary linkage in proteins is the **peptide linkage** (or bond), which is a type of amide bond.
- This bond is formed between the carboxyl group (-COOH) of one amino acid and the amino group (-NH2) of another, resulting in the release of a water molecule (condensation reaction).

3. **Additional Linkages in Proteins**:
- In addition to peptide linkages, proteins may also contain other types of linkages.
- One significant type of linkage is the **disulfide linkage** (or bond), which forms between the sulfur atoms of cysteine residues in the protein.
- This bond contributes to the stabilization of the protein's three-dimensional structure.

4. **Other Possible Linkages**:
- While hydrogen bonds and ionic bonds can also be present in proteins, they are not covalent linkages like peptide and disulfide bonds.
- Hydrogen bonds play a role in the secondary structure of proteins (like alpha-helices and beta-sheets), but they are not classified as linkages in the same way as peptide and disulfide bonds.

5. **Conclusion**:
- Therefore, the two main types of linkages in proteins, in addition to the peptide linkage, are the **disulfide linkage** and potentially other non-covalent interactions, but the disulfide linkage is the primary additional covalent bond.

### Final Answer:
Proteins contain peptide linkages and disulfide linkages in addition to the -CO-NH- linkages.

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