Which mutations cause a frameshift?
Nonsense and deletion
Missense and insertion
Missense and nonsense
Deletion and insertion
The Correct Answer is D
A. Nonsense and deletion: A nonsense mutation occurs when a codon that normally codes for an amino acid is changed into a stop codon, causing premature termination of protein synthesis. Although deletions can cause frameshifts, nonsense mutations themselves do not alter the reading frame. Therefore, this combination does not consistently produce frameshift mutations.
B. Missense and insertion: A missense mutation results from a single nucleotide substitution that changes one amino acid in the protein sequence. This alters protein structure but does not shift the reading frame. While insertions can cause frameshifts, the combination listed does not accurately represent the mechanisms responsible for frameshift mutations.
C. Missense and nonsense: Both missense and nonsense mutations are types of point mutations caused by single base substitutions. These mutations affect the identity of a codon or create a premature stop codon but do not alter the grouping of codons into triplets. As a result, they do not shift the reading frame of the genetic code.
D. Deletion and insertion: Frameshift mutations occur when nucleotides are inserted into or deleted from the DNA sequence in numbers not divisible by three. Because the genetic code is read in triplets (codons), such changes shift the reading frame downstream of the mutation. This alters all subsequent codons and often results in a drastically altered or nonfunctional protein.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
A. Obligate aerobe: An obligate aerobe requires oxygen for growth because it relies on aerobic respiration to produce ATP. Without oxygen, these bacteria cannot generate sufficient energy and will fail to survive. Examples include Mycobacterium tuberculosis and Pseudomonas aeruginosa.
B. Obligate anaerobe: An obligate anaerobe cannot tolerate oxygen and may be killed or inhibited by its presence. These bacteria rely on fermentation or anaerobic respiration for energy and are typically found in oxygen-free environments such as deep tissues or the gastrointestinal tract.
C. Aerotolerant organism: Aerotolerant organisms do not require oxygen for growth but can survive in its presence. They rely on fermentation exclusively and are indifferent to oxygen, unlike obligate aerobes which must have it for survival.
Correct Answer is B
Explanation
A. FAD: FAD (flavin adenine dinucleotide) acts as an electron carrier during cellular respiration, accepting electrons to become FADH₂ in the Krebs cycle. However, it is not the final electron acceptor; it only temporarily shuttles electrons to the electron transport chain.
B. Oxygen: Oxygen is the final electron acceptor in aerobic respiration. At the end of the electron transport chain, oxygen accepts electrons and combines with protons to form water. This step is critical for maintaining the flow of electrons and enabling ATP synthesis via oxidative phosphorylation.
C. Cytochrome c: Cytochrome c is an intermediate electron carrier in the mitochondrial electron transport chain. It transfers electrons between complexes but does not serve as the terminal acceptor of electrons.
D. Pyruvic acid: Pyruvic acid is the end product of glycolysis and can be further metabolized in the Krebs cycle or fermentation pathways. It does not function as an electron acceptor in aerobic respiration.
E. Nitrate: Nitrate can serve as a final electron acceptor in anaerobic respiration for certain bacteria, but in aerobic respiration, oxygen is the ultimate acceptor that drives the complete oxidation of glucose.
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