Which of the following bond is common to all structures of proteins?

Options

A. Peptide bond
B. Hydrogen bond
C. Disulphide linkage
D. Hydrophobic bond

Answer

To determine which bond is common to all structures of proteins, we need to analyze the different levels of protein structure and the types of bonds present in each.

### Step-by-Step Solution:

1. **Understand Protein Structure Levels**:
- Proteins have four levels of structure: primary, secondary, tertiary, and quaternary.

2. **Identify Bonds in Primary Structure**:
- The primary structure of a protein consists of a linear sequence of amino acids. The bond that connects these amino acids is called the **peptide bond**.

3. **Identify Bonds in Secondary Structure**:
- The secondary structure involves the folding of the primary structure into alpha-helices and beta-sheets. In addition to peptide bonds, **hydrogen bonds** are also present to stabilize these structures.

4. **Identify Bonds in Tertiary Structure**:
- The tertiary structure refers to the overall three-dimensional shape of a protein. It includes peptide bonds, hydrogen bonds, and also **disulfide linkages** (covalent bonds between cysteine residues) for stability.

5. **Identify Bonds in Quaternary Structure**:
- The quaternary structure involves the assembly of multiple polypeptide chains. It includes peptide bonds, hydrogen bonds, disulfide linkages, and **hydrophobic interactions**.

6. **Determine the Common Bond**:
- After analyzing all four structures, we find that the **peptide bond** is present in all levels of protein structure (primary, secondary, tertiary, and quaternary).

7. **Conclusion**:
- Therefore, the bond that is common to all structures of proteins is the **peptide bond**.

### Final Answer:
The bond that is common to all structures of proteins is **peptide bond** (Option 1).

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