Final answer:
The AUG codon is known as the start codon because it signals the start of protein synthesis and specifies methionine. Usually removed after initiation, methionine is the first amino acid in the newly synthesized polypeptide. There are 3 stop codons that indicate the end of protein synthesis, and the genetic code is nearly universal across organisms.
Step-by-step explanation:
The AUG codon specifies the amino acid methionine and is often the first codon that begins a polypeptide sequence, which is called a start codon. This start codon establishes the reading frame for translation in the process of synthesizing proteins. The AUG codon is critical because it signals the machinery in a cell to begin protein synthesis, always starting with methionine. Although methionine is the initial amino acid, it is usually removed enzymatically before the completion of the polypeptide chain.
It is important to understand that while AUG is always the initiation codon, not all proteins start with methionine after processing. The genetic code dictates that out of the 64 possible codons, three are designated as stop codons (UAA, UAG, & UGA), which signal the end of protein synthesis. Remarkably, the genetic code is near-universal, with the codons signifying the same amino acids across most organisms.