Question

even though our dna contains billions of base pairs, why are mutations relatively rare? select all that apply the cell cycle has built - in checkpoints to check for errors dna polymerase acts as a proofreader during dna replication ligase breaks down damaged dna uv radiation corrects mutated dna sequences

Explanation:

• The cell cycle has built - in checkpoints to check for errors: These checkpoints (like G1, S, and G2 checkpoints) monitor the cell's progress and can halt the cycle if there are DNA errors, allowing for repair.
• DNA Polymerase acts as a proofreader during DNA replication: DNA polymerase has a 3' - 5' exonuclease activity. If it adds an incorrect nucleotide during replication, it can remove the wrong nucleotide and add the correct one.

• Ligase breaks down damaged DNA: This is incorrect. DNA ligase is involved in joining DNA fragments (e.g., Okazaki fragments during DNA replication) or sealing nicks in the DNA backbone, not in breaking down damaged DNA.
• UV Radiation corrects mutated DNA sequences: UV radiation is a mutagen. It causes mutations (e.g., thymine dimers) in DNA, rather than correcting them. DNA repair mechanisms correct UV - induced damage.

Answer:

• The cell cycle has built - in checkpoints to check for errors
• DNA Polymerase acts as a proofreader during DNA replication