Which of the following codons are referred to STOP codons? Select all that apply.
UAA
UAG
UUU
UGA
Correct Answer : A,B,D
A. UAA: UAA is one of the three termination codons in the genetic code. During translation, when the ribosome encounters UAA on the messenger RNA, it signals the end of protein synthesis. Release factors bind to the ribosome at this codon, causing the completed polypeptide chain to be released from the ribosome.
B. UAG: UAG is another stop codon, sometimes referred to as the “amber” stop codon. Like other termination codons, it does not code for an amino acid. Instead, it recruits release factors that terminate translation and allow the newly synthesized protein to detach from the ribosome.
C. UUU: UUU is not a stop codon; it is a sense codon that codes for the amino acid phenylalanine. During translation, a tRNA carrying phenylalanine recognizes this codon and adds the amino acid to the growing polypeptide chain. Therefore, it functions in protein elongation rather than termination.
D. UGA: UGA is a stop codon often called the “opal” stop codon. When the ribosome encounters UGA on mRNA, translation stops because there is no corresponding tRNA that carries an amino acid for this codon. Instead, release factors bind and trigger the termination of protein synthesis.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
A. Coccus: A coccus is a spherical or round-shaped bacterium. Cocci can exist singly, in pairs (diplococci), chains (streptococci), clusters (staphylococci), or other arrangements depending on their pattern of division. The shape is an important morphological characteristic used in bacterial identification and classification in clinical microbiology.
B. Bacillus: A bacillus refers to a rod-shaped bacterium. Bacilli can occur singly or in chains and may be aerobic or anaerobic. Their elongated shape distinguishes them from cocci and influences how they move, attach to surfaces, and form spores.
C. Vibrio: A vibrio is a comma-shaped or curved rod-shaped bacterium. Vibrio species, such as Vibrio cholerae, are typically associated with aquatic environments and have distinct motility patterns. Their curved morphology differentiates them from cocci and bacilli.
Correct Answer is D
Explanation
A. blocks penetration: Blocking penetration prevents viruses from entering host cells. Nucleotide analogs do not interfere with viral entry; instead, they act after the virus has already penetrated the host cell.
B. inhibits peptidoglycan cross-linking: Peptidoglycan is a component of bacterial cell walls, not viruses. Antibiotics like penicillin target this process, but nucleotide analogs target viral nucleic acid synthesis, not bacterial cell walls.
C. bonds to ergosterol in the cell membrane: Binding to ergosterol is the mechanism of action for antifungal drugs such as amphotericin B. Nucleotide analogs do not interact with membranes or sterols.
D. blocks DNA replication: Nucleotide analogs resemble natural nucleotides and are incorporated into viral DNA or RNA during replication. Once incorporated, they can terminate chain elongation or cause mutations, effectively inhibiting viral DNA replication and viral proliferation.
E. blocks maturation: Blocking maturation interferes with viral assembly or processing of viral proteins, a mechanism seen with protease inhibitors. Nucleotide analogs act earlier in the replication cycle by directly targeting nucleic acid synthesis rather than late-stage viral maturation.
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