Visual Representations · with figure
Use Figure 1 to interpret a gene-expression model. Which statement is most consistent with the figure?
- AMarker A: Ribosomal RNA contributes to peptide-bond formation in the ribosome.
- BMarker B: A start codon helps establish the reading frame for translation.
- CMarker C: Release factors end translation
- DMarker D: Complementary codon-anticodon pairing is requiredcorrect
Why D is correct
Figure 1 must be used to determine which marker is supported by the visual model. Marker D: Codon-anticodon complementarity helps place the correct amino acid during translation. During translation, codon-anticodon base pairing helps place the correct amino-acid-carrying tRNA in the ribosome.
The evidence in the prompt matters before the topic label: "A model shows an mRNA codon positioned in a ribosome and a tRNA carrying an amino acid. Which feature determines...". The supported answer is "tRNA anticodon must be complementary to the mRNA codon" because During translation, codon-anticodon base pairing helps place the correct amino-acid-carrying tRNA in the ribosome. Distractors such as mRNA codon must be copied into a new chromosome first or tRNA must carry a phospholipid instead of an amino acid either ignore the stated pattern or name a related concept without matching the evidence.
Concept Explanation
A point mutation changes an mRNA codon from UAU to UAC. Both codons specify tyrosine. Which type of mutation is this?
- AFrameshift mutation
- BNonsense mutation
- CMissense mutation
- DSilent mutationcorrect
Why D is correct
Because the codon changes but the encoded amino acid remains tyrosine, the mutation is silent.
The stem asks students to explain a specific mechanism, not just recall a unit term: "A point mutation changes an mRNA codon from UAU to UAC. Both codons specify tyrosine. Which type of mutation is this". The correct choice is supported by Because the codon changes but the encoded amino acid remains tyrosine, the mutation is silent. The tempting alternatives such as Frameshift mutation or Nonsense mutation fail because they do not produce the same outcome described in the stem.
Concept Explanation
During translation initiation, a ribosome recognizes a start codon on an mRNA. What is the usual role of the start codon?
- AThe start codon establishes the reading frame and usually codes for methioninecorrect
- BIt signals the ribosome to release the completed polypeptide.
- CIt removes all introns from chromosomal DNA.
- DIt converts the ribosome into a mitochondrion.
Why A is correct
The start codon helps establish the reading frame for translation and usually codes for methionine at the beginning of a polypeptide.
The stem asks for a numerical or quantitative judgment: "During translation initiation, a ribosome recognizes a start codon on an mRNA. What is the usual role of the start...". The safe route is to identify the counted event, use the full denominator, and then interpret the number biologically. Here the worked reasoning is The start codon helps establish the reading frame for translation and usually codes for methionine at the beginning of a polypeptide, so choices based on It signals the ribosome to release the completed polypeptide or It removes all introns from chromosomal DNA lose the required setup.