Night-before review
Read this once, slowly. No new material the morning of the exam.
The one sentence that covers half the course: cells have the same DNA but express different genes, and what you can conclude from an experiment is limited by what the model leaves out.
Six mechanisms you should be able to say out loud in 30 seconds each
- Gene → mRNA → protein → trait, and where RNAi (mRNA) and CRISPR (DNA) each intervene.
- Transcription factors and epigenetic marks set cell identity; four factors reset a skin cell to pluripotency.
- Satellite cells proliferate, then differentiate and fuse into muscle fibers; medium and bioreactor replace blood and body.
- Stem cells plus developmental signals self-organize into an organoid; fusing organoids gives an assembloid.
- Motor cortex → spinal cord → nerves → muscle; a BCI records at the cortex and bypasses the break.
- Restriction enzyme cuts, ligase joins, plasmid carries, host cell expresses.
Four distinctions most likely to decide a question
- RNAi acts on RNA; CRISPR acts on DNA.
- Pluripotent makes every body cell type; totipotent also makes the placenta.
- Genetic engineering is the method; gain of function is the measured outcome, and it does not mean more dangerous.
- Controlling a device is not restoring biological function.
The two limits that appear everywhere
- Diffusion: without blood vessels, oxygen and nutrients reach only a short distance, which caps the thickness of cultured meat and the size and maturity of organoids.
- Scale and context: a result in a dish, a plot, or one participant is evidence for that system, not for a factory, a region, or a population.
Exam-room habits
- For "what does this show" questions, pick the narrowest answer that fits the data.
- Circle the words proves, restores, cures, necessarily, and will — they usually mark the wrong option.
- For short answers, name the mechanism step by step, then name one specific limitation.
- When a question gives you an unfamiliar organism or technology, apply the principle, don't hunt for a memorized fact.
Logistics: phone charged for iClicker, 8:30 in Classroom 311.
How to answer as the doctor or scientist
- Name it plainly. Say what it is in everyday words. Define any term the first time you use it.
- How it works. Walk the mechanism step by step: DNA to mRNA to protein to trait, record to decode to device, and so on.
- Why it might help them. Connect it to the person's own situation and what they care about.
- The honest limit. Say what it cannot do, or what has not been shown yet. Name the specific gap.
- What would tell us more. Name the evidence that would close the gap: a control group, a larger trial, longer follow-up, a test in another environment.
Don't promise: cures, restores, will, proves, necessarily. A patient hears those as guarantees.
Tip: the ← and → arrow keys move between sections.