**Core Concept:**
The primary structure of an amino acid refers to its chemical composition, specifically its carboxyl group (-COOH), amino group (-NH2), and the R-group which varies for each amino acid. This structure determines the amino acid's properties and how it can combine with other amino acids to form a polypeptide chain.

**Why the Correct Answer is Right:**
The correct answer is **D** - **Amino Acid Sequence Detection**. The primary structure of an amino acid is mainly detected by the sequence of amino acids in the polypeptide chain. This sequence is crucial for understanding the protein's function, folding, and interactions with other molecules. The correct reading of the primary structure involves using enzymes called **Reverse Transcriptase** (RT) and **DNA Polymerase** (DNAP) to convert the mRNA sequence into a DNA template, which is then amplified using **Polymerase Chain Reaction (PCR)**.

**Why Each Wrong Option is Incorrect:**
A. **Amino Acid Sequence Translation**: Translating the mRNA sequence into a protein's amino acid sequence is another important step, but it is not responsible for detecting the primary structure.
B. **Protein Sequence Detection**: Detecting the protein sequence is crucial, but it is not the same as detecting the primary structure.
C. **Peptide Bond Formation**: Although peptide bonds are essential for the polypeptide chain, this option does not address the detection of the primary structure.

**Clinical Pearl / High-Yield Fact:**
Understanding the primary structure is essential for several reasons:
1. **Protein Function**: Variations in the amino acid sequence can lead to different protein functions, such as enzymes, hormones, or antibodies.
2. **Protein Folding and Interactions**: The primary structure determines how the protein will fold and interact with other molecules, such as enzymes, receptors, or drugs.
3. **Genetic Disorders**: Mutations in the primary structure can cause genetic disorders, as seen in cystic fibrosis caused by mutations in the CFTR gene's primary structure.

**Explanation:**
The primary structure of amino acids is crucial for understanding proteins and their functions. Amino acids are synthesized in the cytoplasm of cells, and then assembled into polypeptide chains during translation. The amino acid sequence is determined by the mRNA sequence and starts with the AUG codon (UUU/UAC) for methionine.

**Detecting the Primary Structure:**
The primary structure is determined by the amino acid sequence, which is translated from the mRNA sequence. The primary structure is detected by **Reverse Transcription Polymerase Chain Reaction (RT-PCR)**, which converts the mRNA sequence into a DNA template, allowing for amplification using Polymerase Chain Reaction (PCR) to generate copies of the DNA template. This DNA template is then sequenced using techniques like **Sanger sequencing** to identify the specific amino acid sequence.

**Why Option D is Correct:**
The correct answer is D, "Amino Acid Sequence Detection". Amino acid sequences are translated from the mRNA sequence and detected through RT