Which statement is true about the genetic code?

Which statement is true about the genetic code?

• A. All 64 codons code for amino acids
• B. Exactly 61 codons code for amino acids and 3 are stop codons
• C. There are 64 stop codons
• D. There are 64 codons that code for amino acids

Answer: (D)

Codons are triplets of RNA bases that specify which amino acids will be added during protein synthesis. Because there are four nucleotides and codons are three bases long, there are 4^3 = 64 possible codons. Not all of these codons code for amino acids: three of them act as stop signals (UAA, UAG, UGA) that tell the ribosome to terminate translation. This leaves 61 codons that code for amino acids, with redundancy so that some amino acids are specified by more than one codon. The statement that there are 64 codons coding for amino acids would ignore the stop codons, which is why the accurate view is that there are 64 codons in total, 61 coding for amino acids and 3 serving as stop signals.

Codons are triplets of RNA bases that specify which amino acids will be added during protein synthesis. Because there are four nucleotides and codons are three bases long, there are 4^3 = 64 possible codons. Not all of these codons code for amino acids: three of them act as stop signals (UAA, UAG, UGA) that tell the ribosome to terminate translation. This leaves 61 codons that code for amino acids, with redundancy so that some amino acids are specified by more than one codon. The statement that there are 64 codons coding for amino acids would ignore the stop codons, which is why the accurate view is that there are 64 codons in total, 61 coding for amino acids and 3 serving as stop signals.