Yes, DNA does have codons.
Understanding Codons
A codon is a sequence of three DNA or RNA nucleotides that codes for a specific amino acid or a stop signal during protein synthesis. These triplets of nucleotides are the fundamental units of the genetic code. Think of them as three-letter words that make up the sentences (proteins) a cell uses to function.
- DNA's Role: DNA contains the master blueprint for building proteins. The sequence of nucleotides in DNA dictates the sequence of codons.
- RNA's Role: The DNA sequence is transcribed into messenger RNA (mRNA), which then carries the codon information to the ribosome.
- Protein Synthesis: At the ribosome, transfer RNA (tRNA) molecules, each carrying a specific amino acid, recognize and bind to the codons on the mRNA. This process, called translation, assembles amino acids into a polypeptide chain, which folds into a functional protein.
- Stop Codons: Three codons (UAA, UAG, and UGA) signal the end of protein synthesis. These are crucial to ensure the protein chain is complete and properly terminated.
Examples of Codons in DNA
While the codons are usually discussed in the context of mRNA (because that's what's directly read by the ribosome), the underlying sequence originates in DNA. For example, the DNA sequence GGG could be transcribed to GGG in mRNA, which then codes for the amino acid glycine. A different DNA sequence, such as AAT, might translate to AAU in mRNA, coding for asparagine.
The provided references highlight several key aspects of codons within the DNA sequence:
- The reference on the Genome.gov glossary explicitly states that a codon is a sequence of three nucleotides in DNA or RNA.
- Nature's Scitable explains that stop codons signal the end of protein synthesis, a process dependent on the codons encoded in the original DNA.
- Learn.Genetics.Utah.edu emphasizes the three-letter DNA sequence nature of codons and their role in encoding specific amino acids.
- A study on the AT-rich Drosophila genome further supports the presence of stop codons, which are derived from DNA.
- The reference discussing sheep scrapie resistance mentions polymorphisms in codons, proving that these codons are encoded by the DNA sequence.
