SAT II Biology M : DNA Replication and Repair

Study concepts, example questions & explanations for SAT II Biology M

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Example Questions

Example Question #1 : Dna Replication And Repair

What type of mutation will code for an amino acid but not the correct or desired amino acid?

Possible Answers:

Insertion mutation

Missense mutation

Silent mutation

Nonsense mutation

Deletion mutation

Correct answer:

Missense mutation

Explanation:

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.

Example Question #2 : Dna, Rna, And Proteins

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'

Possible Answers:

5' - UAGCUUCACG - 3'

5' - TAGCTTCACG - 3'

5' - ATCGAAGTGC - 3'

3' - UAGCUUCACG - 5'

3' - TAGCTTCACG - 5'

Correct answer:

5' - TAGCTTCACG - 3'

Explanation:

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'

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