Final answer:
In mRNA, a codon is a group of three nucleotides that specify a particular amino acid during protein synthesis. Sixty-one codons encode amino acids, while three function as stop codons. The start codon AUG also signifies the amino acid methionine and the initiation of translation.
Step-by-step explanation:
Understanding Codons in mRNA
The mRNA contains groups of three nucleotides that are crucial for the synthesis of proteins. These groups are known as codons, and each codon corresponds to a specific amino acid. When the process of translation occurs, the sequence of these codons in the mRNA determines the sequence of amino acids in the polypeptide that is being synthesized. Not all codons encode for amino acids; some are involved in the termination of protein synthesis. These are known as stop codons. The genetic code includes 64 possible codon combinations, with 61 coding for amino acids and three serving as stop codons. The initiation of protein synthesis often starts with the codon AUG, which codes for the amino acid methionine and also acts as the start codon.
It is important to note that the genetic code is 'degenerate,' meaning that multiple codons can specify the same amino acid. This redundancy helps protect the protein-coding process from mutations. During the translation process, an anticodon sequence pairs with the mRNA codon to ensure the correct amino acid is incorporated into the growing polypeptide chain.