## **Core Concept**
Codons are sequences of nucleotides that correspond to a specific amino acid or stop signal during protein synthesis. They are fundamental to the process of translating messenger RNA (mRNA) into a polypeptide chain. The genetic code is nearly universal, with 64 codons specifying 20 amino acids and three stop signals.

## **Why the Correct Answer is Right**
The correct answer, **mRNA (messenger RNA)**, is the molecule that directly participates in the translation process, where codons are read by the ribosome to assemble amino acids into a polypeptide chain. Each codon on the mRNA is recognized by a specific transfer RNA (tRNA) molecule, which brings the corresponding amino acid to the ribosome.

## **Why Each Wrong Option is Incorrect**
- **Option A: DNA** - While DNA contains the genetic information that is transcribed into mRNA, the codons themselves are not present on DNA in the context of protein synthesis. Instead, DNA sequences are transcribed into mRNA, which then contains the codons.
- **Option B: tRNA** - tRNA molecules recognize codons on mRNA through their anticodons but do not contain codons themselves. They play a crucial role in translating the genetic code by bringing the appropriate amino acids to the ribosome.
- **Option D: rRNA** - rRNA (ribosomal RNA) is a component of ribosomes, which are the sites of protein synthesis. While rRNA is essential for the translation process, it does not contain codons.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that mutations in DNA can lead to changes in codons on mRNA, potentially altering the amino acid sequence of proteins (missense or nonsense mutations). This can have significant clinical implications, including genetic disorders or cancer.

## **Correct Answer:** C. mRNA.