## Core Concept
The primary structure of a protein refers to the sequence of amino acids linked by peptide bonds. This linear sequence is crucial for determining the overall 3D structure and function of the protein. The primary structure is formed through a specific type of chemical bond.

## Why the Correct Answer is Right
The correct answer involves **peptide bonds**, which are formed between the carboxyl group of one amino acid and the amino group of another. This process is a condensation reaction where water is released, and it is essential for creating the primary structure of proteins. Peptide bonds are strong covalent bonds that link amino acids in a chain.

## Why Each Wrong Option is Incorrect
* **Option A:** Hydrogen bonds are involved in the secondary, tertiary, and quaternary structures of proteins, not the primary structure. They are weaker than peptide bonds and play a role in the stability of the protein's 3D conformation.
* **Option B:** Ionic bonds (or salt bridges) contribute to the stability of the tertiary and quaternary structures of proteins. They are not responsible for the primary structure.
* **Option D:** Disulfide bridges are also involved in the stability of the tertiary structure of proteins. They are covalent bonds but are not responsible for linking amino acids in the primary structure.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the primary structure of a protein is determined by the sequence of nucleotides in the gene encoding that protein. Alterations in this sequence, such as point mutations, can lead to changes in the amino acid sequence (missense or nonsense mutations), potentially affecting protein function.

## Correct Answer: C.