Why does a chain of amino acids eventually stop synthesizing?

Answer 1

The codons on mRNA are the pattern for the anticodons on tRNA to match. tRNA brings the amino acids.

Three different codons in mRNA are called "stop" codons. They signal the end of the polypeptide chain. So the chain breaks off, folds up, and the protein is made. The stop codons are UAA, UAG, and UGA.