SAT Subject Test in Biology › DNA Replication and Repair
What type of mutation will code for an amino acid but not the correct or desired amino acid?
Missense mutation
Silent mutation
Nonsense mutation
Deletion mutation
Insertion mutation
By definition, a missense mutation will still code for an amino acid, but not the desired amino acid. Silent mutations will have a different base pair, but due to the redundancy of genetic code, it will still code for the desired mutation. Nonsense mutations code for an amino acid that leads to a stop codon, which terminates the translation of mRNA into protein. Insertions and deletions result in a shifted reading frame and typically are detrimental.
Given the partial sequence of a single DNA strand shown below, what will be the sequence of the complementary strand that is produced during DNA replication?
3' - ATCGAAGTGC - 5'
5' - TAGCTTCACG - 3'
3' - TAGCTTCACG - 5'
5' - ATCGAAGTGC - 3'
5' - UAGCUUCACG - 3'
3' - UAGCUUCACG - 5'
The question specifies that this is DNA replication. U (uracil) is found only in RNA and T (thymine) is found only in DNA. In DNA, A (adenine) pairs with T (thymine) and G (guanine) pairs with C (cytosine) so the complementary strand will have "A" where the original has "T," "G" where the original has "C," "C" where the original has "G" and "T" where the original has "A."
DNA strands run antiparallel, so the 3' end on the new strand will go opposite the 5' end on the original and vice versa. In this case, that means the complementary strand will run from 5' to 3' to read 5' - TAGCTTCACG - 3'. This sequence is shown in bold below:
5' - TAGCTTCACG - 3'
3' - ATCGAAGTGC - 5'