7 public questions tagged with this topic.
A nonsense mutation results in a premature stop codon, leading to incomplete protein synthesis.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance DNA Structure Double Helix and Packaging - Nucleosome
Nonsense reflects key principle in quiz on molecular evolution, where evolutionary mechanisms shape genetic variation and adaptation. In this context, Nonsense aligns with experimental and theoretical evidence from population genetics, behavioral ecology and molecular phylogeny. Textbooks like Campbell Biology, Futuyma Evolution and Hartl Principles illustrate supporting data. Understanding why Nonsense fits helps integrate natural selection, environment.
Ref: Li, Molecular Evolution, Neutral Theory and Molecular Clocks.
Universal code designates UGA as termination codon yet selenoproteins conserve in-frame UGA at catalytic centers for Sec insertion requiring recoding. Surveys show all confirmed vertebrate, bacterial, archaeal selenoproteins use UGA exclusively; UAA or UAG never encode selenium. Reason stems from anticodon compatibility, tRNASec UCA pairs perfectly with UGA requiring single modification, other stops would need different isoacceptors. Conservation allows kinetic competition control between release factor and SelB or EFSec. Fidelity depends on SECIS presence and selenium status, ensuring efficiency regulated by nutrient availability and release factor competition dynamics.
Ref: NCBI Bookshelf, Codon Usage: UGA as Selenocysteine Codon in Selenoproteins
Standard genetic code assigns three codons to termination: UAA ochre, UAG amber, UGA opal, recognized by release factor RF2 in bacteria and eRF1 in eukaryotes triggering peptidyl-tRNA hydrolysis and ribosome dissociation. Sixty-one codons encode amino acids, three terminate. In most transcripts UGA functions as stop, least frequent in highly expressed bacterial genes. Its dual use for selenocysteine illustrates conditional reassignment where mRNA context redefines meaning, yet default decoding terminates protein synthesis. This plasticity demonstrates evolutionary flexibility where infrequent stop codon allows occasional recoding without globally disrupting proteome termination fidelity essential for accurate translation.
Ref: NCBI Bookshelf, Molecular Biology: Genetic Code – Stop Codons and UGA Function
Eukaryotic termination employs two factors with distinct roles coordinated for release. eRF1 is a class I release factor that structurally mimics tRNA and enters the A-site, where its N-terminal domain recognizes UAA, UAG, and UGA stop codons via conserved TASNIKS and other motifs, providing omnipotent decoding unlike bacterial split systems. Its central domain bearing the methylated GGQ motif then catalyzes hydrolysis of peptidyl-tRNA ester bond in peptidyl transferase center. eRF3 is a GTPase that stimulates termination fidelity and recycling but does not decode stops. Bacterial RF1 and RF2 split codon specificity, contrasting with single eukaryotic factor approach.
Ref: Alberts Molecular Biology of the Cell Ch6; NCBI - eRF1 decodes stop codons in eukaryotes, class I release factor
Stop codons UAA, UAG, UGA are not recognized by any tRNA but by protein release factors that mimic tRNA shape. In bacteria RF1 decodes UAA and UAG, RF2 decodes UAA and UGA, while in eukaryotes eRF1 recognizes all three. They bind A site when stop codon occupies decoding center, inducing conformational change that positions GGQ motif in peptidyl transferase center to catalyze hydrolysis of P-site peptidyl-tRNA ester bond, freeing protein. Class II factors eRF3 or RF3 GTPases accelerate factor binding and recycling thereafter.
Ref: Berg et al., Biochemistry, 9th ed., Chapter 32, Release factors recognizing stop codons – RF1, RF2, eRF1
UAA, UAG, UGA is the scientifically accurate answer to this question. Within the study of Acid, Base, pH, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of UAA, UAG, UGA directly address what is being asked. Among the other options, AUG, GUG, UUG, AAA, GAA, CAA, and UUC, UUA, UUG do not correctly answer this question because they either refer to different concepts, describe properties of other molecules or processes, or represent common misconceptions about this topic.
Ref: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 2
