Researchers found a strain of E. coli bacteria that had mutation rates one hundred times higher than normal. Which of the following statements correctly describes the most likely cause of these mutations?

• A. The single-stranded binding proteins were malfunctioning during DNA replication.
• B. There were one or more mutations in the RNA primer.
• C. The proofreading mechanism of DNA polymerase was malfunctioning.
• D. The DNA polymerase was unable to add bases to the 3′ end of the growing DNA strand.

Answer: (C)

Verified step by step guidance

1. Understand the role of DNA polymerase in DNA replication. DNA polymerase is responsible for adding nucleotides to the growing DNA strand and has a proofreading function to correct errors.
2. Recognize that a malfunction in the proofreading mechanism of DNA polymerase can lead to an increased mutation rate. Normally, DNA polymerase checks and corrects mismatched bases during replication.
3. Consider the impact of a malfunctioning proofreading mechanism. Without proper proofreading, errors in base pairing are not corrected, leading to a higher frequency of mutations.
4. Evaluate the other options provided. Single-stranded binding proteins stabilize the unwound DNA, RNA primers are necessary for initiating replication, and the inability to add bases to the 3' end would halt replication, not increase mutation rates.
5. Conclude that the most likely cause of the increased mutation rate is the malfunctioning proofreading mechanism of DNA polymerase, as it directly affects the accuracy of DNA replication.