If the wild type DNA sequence reads THE CAT ATE THE BIG RAT, what type of mutation would change the sequence to THE CAT ATE (stop)?
Deletion
Nonsense
Silent
Missense
Insertion
The Correct Answer is B
A. Deletion: A deletion mutation removes one or more nucleotides from the DNA sequence. While deletions can lead to frameshifts and potentially premature stop codons, the key feature in this scenario is the introduction of a stop signal, not the removal of nucleotides per se.
B. Nonsense: A nonsense mutation changes a codon that encodes an amino acid into a stop codon. In this example, “THE CAT ATE THE BIG RAT” is truncated to “THE CAT ATE (stop),” indicating translation terminates prematurely. This type of mutation produces a truncated, usually nonfunctional protein.
C. Silent: A silent mutation changes a nucleotide without altering the amino acid sequence. It does not produce a stop codon or truncate the protein, so it would not result in “THE CAT ATE (stop).”
D. Missense: A missense mutation changes a codon so that a different amino acid is incorporated. While it alters the protein sequence, it does not introduce a stop codon, so it cannot account for the premature termination seen here.
E. Insertion: An insertion adds one or more nucleotides into the sequence. Like deletions, insertions can cause frameshifts that might eventually produce a stop codon, but the defining characteristic in this example is the direct conversion of a codon to a stop codon, making this a nonsense mutation rather than a generic insertion.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
A. cell membrane; cytoplasm: Viral replication does not generally occur at the cell membrane. The membrane may be involved in viral entry or exit (such as budding in enveloped viruses), but it is not the primary site where viral genomes replicate. DNA viruses require access to host nuclear enzymes, while most RNA viruses replicate within the cytoplasm.
B. cytoplasm; nucleus: This arrangement reverses the typical replication locations of DNA and RNA viruses. Most DNA viruses depend on host DNA polymerases and transcription machinery located in the nucleus. In contrast, most RNA viruses replicate in the cytoplasm because they carry or encode their own RNA-dependent RNA polymerase.
C. nucleus; cytoplasm: Most DNA viruses replicate in the nucleus because they rely on host cell enzymes for DNA replication and transcription, which are located there. Most RNA viruses replicate in the cytoplasm, where viral RNA polymerases synthesize new RNA genomes and messenger RNA without needing host nuclear machinery.
D. nucleus; endoplasmic reticulum: While the endoplasmic reticulum is involved in protein synthesis and processing of viral proteins, it is not typically the primary location of RNA genome replication. RNA viruses generally replicate their genomes freely in the cytoplasm rather than within the endoplasmic reticulum.
E. cytoplasm; cell membrane: DNA viruses typically replicate in the nucleus rather than the cytoplasm. Additionally, the cell membrane is not a location for viral genome replication. Although some viruses assemble or bud at the membrane, genome synthesis primarily occurs either in the nucleus (DNA viruses) or cytoplasm (RNA viruses).
Correct Answer is B
Explanation
A. lag phase: The lag phase is the initial period after bacteria are introduced into a new environment. During this phase, cells are metabolically active but not dividing at a significant rate as they adapt to the new conditions. There is little to no increase in cell number, so it does not represent the phase of maximum cell division.
B. exponential (or log) phase: The exponential or log phase is characterized by rapid, logarithmic cell division, where the population doubles at a constant and maximal rate. Nutrients are abundant, waste products are minimal, and environmental conditions are optimal, making this the period of maximum bacterial growth and replication.
C. prophase: Prophase is a stage of eukaryotic mitosis and is not applicable to bacterial growth. Bacteria reproduce through binary fission rather than mitosis, so prophase does not occur in their growth cycle.
D. stationary phase: The stationary phase occurs when the growth rate slows and stabilizes because nutrient depletion and accumulation of waste products limit further cell division. The number of new cells equals the number of dying cells, so this is not the phase of maximal cell division.
E. death phase: The death phase is marked by a decline in the bacterial population due to nutrient exhaustion, toxic accumulation, and unfavorable environmental conditions. Cell death exceeds new cell formation, representing the opposite of maximal growth.
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