Use the helix model to explain base pairing and strand direction
Three steps, the way the exam actually works: work through the lab, write down your own observations, then answer a 6-point free response. What you recorded goes to the grader with your writing, so a conclusion that does not follow from your own evidence will cost you the point — exactly as it would with a real reader.
Run the investigation
- 1Rotate the DNA model and identify several A–T and G–C base pairs.
- 2Record which bases pair together and which structural parts form the outside of the helix.
- 3Trace the two strands visually and note their opposite directions.
- 4Use the model to predict how complementarity supports replication.
Booting the lab…
Record what you found
This is your reading of the source, not ours. The grader sees them, so your conclusions have to follow from what you actually recorded.
| Base paired with adenine | |
|---|---|
| Base paired with guanine | |
| What forms the outside backbone | |
| Relationship between strand directions |
Answer the free response
The DNA model makes structure visible. (a) Explain how complementary base pairing supports semiconservative replication. (b) State what “antiparallel” means in DNA and explain why the strands must run in opposite directions for replication enzymes to work correctly. (c) Explain why a change from G–C to A–T can matter even though the helix diameter stays nearly constant. (d) A student says the sugar–phosphate backbone is the information-bearing part of DNA because it is on the outside where enzymes can reach it. Evaluate that claim.
Sign in to have this graded and saved to your progress.