Year 10 Science · Unit 1 · Lesson 3
Challenge Worksheet
Learning Goals
What if…?
Scenario
DNA polymerase normally makes roughly one error per billion base pairs copied, thanks to a built-in proofreading function that detects and corrects mismatched bases. Imagine that a genetic change completely abolished this proofreading ability in all human cells, DNA polymerase could still add nucleotides, but it could no longer remove and replace incorrect ones.
(a) Predict what would happen to the mutation rate in body cells. Would the effect be the same in all tissues? Explain, considering that cells like skin and gut lining divide more frequently than brain cells.
(b) Cancer occurs when mutations accumulate in genes that control cell division. Using this information, predict how the removal of proofreading would affect cancer risk and at what age cancers might typically develop.
(c) Evolution depends on heritable variation, which comes partly from mutations passed through gametes (sex cells). Would a higher mutation rate necessarily speed up evolution? Explain why higher mutation rates can be both helpful (more variation) and harmful (lethal mutations) for a species.
1. Some cancer drugs work by targeting DNA polymerase or other enzymes involved in DNA replication, preventing cancer cells from dividing. However, these drugs can also harm healthy cells. Using your knowledge of DNA replication and which body cells divide most rapidly, predict which tissues would be most damaged by such a drug and why.
2. The average human cell makes fewer than one error per billion base pairs during DNA replication. Calculate approximately how many errors would occur each time a human cell replicates its entire genome of 6.4 billion base pairs. What does this tell you about the importance of proofreading?
Wrap Up
In one sentence, what was the main idea of this lesson?