Subject: Order of bases in stop codons.

Why is the termination (stop) codon, which signals the end of a protein, only in these three orders: uracil-adenine-adenine(UAA), uracil-adenine-guanine(UAG), or uracil-guanine-adenine (UGA)?

I recently learned about DNA, RNA, and codons in my molecular biology class. I know that DNA is the abbreviation for deoxyribonuleic acid which is the heredity material of most organisms and it also makes genes. RNA strands or ribonucleic acid and it is the heredity material of certain viruses. In our studies, I discovered that codons are a group of three nucleotide bases in the messenger RNA molecule that codes for an amino acid in a protein sequence. The initiator (start) codon, which signals the beginning of a protein, is adenine-uracil- guanine (AUG). The start codon is AUG because it also codes for the amino acid, methionine, but enzymes may later cleave it off. I am curious about the stop codons. I hope someone would answer my question so it could help me understand better. I would appreciate any answers or replies. Thank you.

Sincerely,
Alison Wong

c/o Ms. St. John
rstjohn@webtv. net

Re: Order of bases in stop codons.