Codons are the fundamental units of genetic code. They are three-nucleotide sequences found in both DNA and RNA that specify a particular amino acid during protein synthesis. Think of them as the "words" in the genetic "sentence" that instruct cells to build proteins.
Understanding Codons: A Deeper Dive
-
Three-Nucleotide Sequence: Each codon consists of three consecutive nucleotides (adenine, guanine, cytosine, or uracil in RNA; adenine, guanine, cytosine, or thymine in DNA). These nucleotides are the building blocks of nucleic acids. Examples include AUG, UAA, and GCU.
-
Amino Acid Specificity: Each codon codes for a specific amino acid. For example, AUG codes for methionine, a common amino acid. However, the genetic code is degenerate, meaning most amino acids are coded by multiple codons.
-
Start and Stop Signals: Some codons don't code for amino acids; instead, they act as signals to start or stop protein synthesis. AUG typically serves as the start codon, and UAA, UAG, and UGA are common stop codons.
-
Total Number of Codons: There are 64 possible codons (4 nucleotides3). This redundancy allows for variations in the genetic code while maintaining the overall function.
-
Importance in Protein Synthesis: Codons are crucial for translating the genetic information stored in DNA into functional proteins. The sequence of codons determines the sequence of amino acids in a protein, thus influencing its structure and function. The process involves transcription (DNA to RNA) and translation (RNA to protein).
Examples of Codons and their Amino Acids:
- AUG: Methionine (Met, M) - Often the start codon
- UAA: Stop codon
- GCU: Alanine (Ala, A)
- UGG: Tryptophan (Trp, W)
The information provided across multiple sources confirms that a codon is a three-nucleotide sequence in DNA or RNA that directs the synthesis of a specific amino acid or signals the start or stop of the process. The genetic code is degenerate, meaning that several codons may specify the same amino acid, and this is a key aspect of its functionality. The AUG codon commonly initiates protein synthesis, while UAA, UAG, and UGA act as stop codons.
