Primary structure of proteins is due to the presence of

Options

A. peptide bonds
B. disulphide (S-S) linkages
C. hydrogen bonds
D. ionic bonds

Answer

### Step-by-Step Solution:

1. **Understanding Primary Structure**: The primary structure of a protein refers to its linear sequence of amino acids. This sequence is crucial because it determines the protein's overall shape and function.

2. **Amino Acids as Building Blocks**: Proteins are polymers made up of monomers called amino acids. Each protein consists of a specific sequence of these amino acids linked together.

3. **Formation of Peptide Bonds**: The amino acids are joined together through a specific type of covalent bond known as a peptide bond. This bond forms during a condensation reaction, where a molecule of water is released.

4. **Structure of Amino Acids**: Each amino acid has a central carbon (alpha carbon), an amino group (NH2), a carboxyl group (COOH), a hydrogen atom (H), and a variable side chain (R group) that distinguishes one amino acid from another.

5. **Peptide Bond Formation**: When two amino acids come together, the carboxyl group of one amino acid reacts with the amino group of another, resulting in the release of water (H2O) and the formation of a peptide bond (–CO–NH–).

6. **Linear Arrangement**: The sequence of amino acids linked by peptide bonds forms a straight chain, which is characteristic of the primary structure. There are no branches or coils in this structure.

7. **Conclusion**: Therefore, the primary structure of proteins is primarily due to the presence of peptide bonds that link the amino acids in a linear sequence.

### Final Answer:
The primary structure of proteins is due to the presence of **peptide bonds**.

---