What type of mutation alters the base, but not the amino acid being coded for?
Point
Nonsense
Back
Silent
Missense
The Correct Answer is D
A. Point: A point mutation involves a change in a single nucleotide base in the DNA sequence. While it describes the location of the change, it does not specify the effect on the amino acid. A point mutation can result in silent, missense, or nonsense outcomes depending on the codon affected.
B. Nonsense: A nonsense mutation changes a codon to a stop codon, prematurely terminating protein synthesis. This produces a truncated and usually nonfunctional protein, which is distinct from a mutation that does not alter the amino acid sequence.
C. Back: A back mutation (or reverse mutation) occurs when a mutated gene reverts to its original sequence. While this restores the original function, it is not the type of mutation that leaves the amino acid unchanged on the first occurrence.
D. Silent: A silent mutation changes a nucleotide base in the DNA but does not alter the amino acid sequence due to the redundancy of the genetic code. For example, both GAA and GAG code for glutamic acid, so a change from A to G at the third base is silent. This mutation does not affect protein function but may still influence gene expression in rare cases.
E. Missense: A missense mutation changes a single nucleotide and results in a different amino acid being incorporated into the protein. This can alter protein function and structure, unlike a silent mutation which leaves the amino acid unchanged.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
A. double-stranded DNA: In double-stranded DNA, Chargaff’s rules apply: adenine pairs with thymine and guanine pairs with cytosine, so the percentages of A and T should be roughly equal, as should G and C. The viral nucleic acid shows 20% adenine and only 10% thymine, and 40% guanine with 30% cytosine, which violates these pairing rules, indicating it unlikely.
B. double-stranded RNA: Double-stranded RNA also follows base-pairing rules, with adenine pairing with uracil instead of thymine, and guanine pairing with cytosine. The unequal proportions of bases in this viral genome (e.g., A ≠ U, G ≠ C) suggest that it is not double-stranded RNA.
C. single-stranded RNA: Single-stranded RNA does not require complementary base pairing between strands, allowing unequal proportions of the four nucleotides. The observed percentages of adenine, guanine, cytosine, and thymine/uracil can vary widely, consistent with the data provided. This pattern supports the conclusion that the viral nucleic acid is single-stranded RNA.
D. single-stranded DNA: While single-stranded DNA does not require base pairing, thymine would still be present rather than uracil. However, the high guanine content (40%) and low thymine (10%) are unusual; still, the presence of thymine rather than uracil suggests that if it were RNA, thymine would be replaced with uracil, making single-stranded RNA more likely.
Correct Answer is E
Explanation
A. Catabolism: Catabolism refers specifically to the breakdown of complex molecules into simpler ones, releasing energy in the process. While it is a component of cellular chemical reactions, it does not encompass all the reactions in the cell.
B. Phosphorylation: Phosphorylation is a specific chemical process in which a phosphate group is added to a molecule, often regulating protein function or producing ATP. It represents only one type of reaction within the cell and is not synonymous with all cellular chemical reactions.
C. Redox reactions: Redox (reduction-oxidation) reactions involve the transfer of electrons between molecules and are critical for energy production. However, they are just a subset of cellular reactions and do not cover all metabolic processes.
D. Cellular respiration: Cellular respiration is the process by which cells convert nutrients into ATP and includes glycolysis, the Krebs cycle, and the electron transport chain. Although it involves numerous chemical reactions, it is only one pathway within the broader scope of cellular metabolism.
E. Metabolism: Metabolism refers to the sum of all chemical reactions that occur within a cell, including both anabolic (building) and catabolic (breaking down) processes. It encompasses energy production, biosynthesis, and the regulation of cellular activities, making it the comprehensive term for all cellular chemical reactions.
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