How many stop codons are there and what are their names?
There are three stop codons in the genetic code: UAA, UAG, and UGA. Stop
codons, also known as termination codons, signal the end of the protein-coding
sequence during translation. When a ribosome reaches a stop codon, it releases the
newly synthesized protein and the components of the translation complex dissociate.
The consequences of a mutation that creates a premature stop codon can vary.
Depending on the location and nature of the mutation, the resulting protein may be
truncated, unstable, or absent. Such mutations are a common cause of genetic
disorders such as cystic fibrosis, Duchenne muscular dystrophy, and some forms of
inherited blindness.
Interestingly, some organisms have evolved alternative genetic codes that use
different stop codons. For example, some bacteria and archaea use UAG as a codon
for the amino acid selenocysteine, while certain ciliates utilize UGA for glutamine.
These variations highlight the flexibility of the genetic code and its potential for
evolution.
In summary, stop codons play a crucial role in the faithful decoding of genetic
information during translation. Their importance is underscored by the phenotypic
consequences of mutations that disrupt their function.
References:
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2. Kozak M. Point mutations define a sequence flanking the AUG initiator codon that
modulates translation by eukaryotic ribosomes. Cell. 1986 Mar 28;44(6):283-92. doi:
10.1016/0092-8674(86)90762-2. PMID: 3943123.
3. Scolnick E, Tompkins R, Caskey T, Nirenberg M. Release factors differing in specificity for
terminator codons. Proc Natl Acad Sci U S A. 1968 Jan;59(1):112-9. doi:
10.1073/pnas.59.1.112. PMID: 4386875.