Transcribe and translate a gene, then break it
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.
Predict before you look
- RNA is built by complementary base pairing against DNA, but with one substitution. Which base does RNA use in place of thymine?
- How many bases make one codon, and how many amino acids does a stop codon contribute to the finished protein?
Nothing to submit here — these are to think through, so the prediction below is an informed one rather than a guess.
Commit to an answer now. It is not graded and being wrong costs nothing — the point is to have something specific to reconcile against once you have the data.
Answer every prediction to unlock the lab. A sentence is enough.
Run the investigation
Predictions first
The procedure and the simulation unlock once you have committed above. Observing before predicting is how a wrong intuition survives a lab intact.
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.
| Template DNA strand | |
|---|---|
| mRNA strand transcribed from it | |
| Amino-acid sequence produced | |
| Codons read before the stop codon |
Answer the free response
Using the strand this lab generated for you: (a) Explain the base-pairing rule that produced your mRNA from your template strand, and account specifically for why no thymine appears anywhere in your mRNA. (b) Identify the codon that began translation and the codon that ended it, and explain what the reading frame is and why it matters. (c) Suppose a single base in the template strand were substituted. Describe the three possible consequences for the resulting protein and name each type of mutation. (d) A single base is instead deleted near the start of the coding sequence. Explain why this is usually far more damaging than a substitution.
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