Bacterial Transformation

Predict growth separately from fluorescence

Before incubation, make a prediction for each supplied plate using three labels: plasmid present or absent, antibiotic present or absent, and arabinose present or absent. Compare colony growth in ordinary light, then record fluorescence under UV as a separate observation. Keeping plate identity attached to both observations prevents a bright colony from standing in for every control.

For an explanation task, compare the plasmid-bearing antibiotic plate with the plasmid-bearing antibiotic-plus-arabinose plate. Growth and fluorescence support different claims about resistance and reporter expression. Use the no-plasmid antibiotic control to test whether selected growth can be explained without plasmid uptake, then compare the heat-shock treatments without changing the plate composition. Record plate label, treatment, colony count, viewing light, and fluorescence; do not invent a colony total before running the model.

The existing course image is the preview; no new video is promised here. Continue with gel electrophoresis and PCR for a different DNA evidence task, or choose an AP Biology practice path.

The question behind the experiment

A bacterium can acquire a plasmid yet express a visible reporter only under a particular condition. This investigation separates transformation, antibiotic selection, and gene expression through a controlled plate comparison. Identify what DNA is added and what each plate contains before predicting growth. The goal is to explain the pattern across the plates, not merely to find a glowing colony. A single positive-looking plate cannot establish which step caused the pattern without the corresponding negative and growth controls.

Plan a useful comparison

Compare bacterial preparations with and without the plasmid while retaining the treatment and transfer volumes. The course models calcium-chloride preparation and heat shock as steps helping some bacteria take up external DNA. Transformation affects only part of the population. Do not assume that every cell receiving the preparation acquires the plasmid. Write down which preparation is plated and how much is transferred, because a colony count later represents only the plated fraction of the original mixture under the modeled procedure.

Connect the observation to the model

Use plates with and without antibiotic to distinguish general viability from selected growth. Growth without antibiotic shows that bacteria can survive the preparation and grow under that plate condition. Growth on antibiotic supports the selected resistance phenotype in the corresponding preparation. A no-plasmid antibiotic plate provides a control for the selection. Explain each outcome by reference to both the bacterial preparation and the medium; the same label positive or negative can refer to different evidence when those conditions are left unstated.

Interpret the result carefully

Compare the reporter on plates with and without arabinose under the course's viewing conditions. A resistance-bearing colony can grow without displaying the same fluorescence as an induced colony. Gene presence and gene expression are therefore separate claims supported by different comparisons. The inducer changes the modeled expression regulation rather than creating a new reporter gene in the cell. Keep ordinary colony growth and fluorescence observations in separate fields so the visual result does not replace the selection evidence in your interpretation.

Build an explanation from your evidence

Calculate transformation efficiency using the amount of DNA and the proportion of the preparation actually plated, following the course procedure. A raw colony total is not sufficient if plating fractions differ between samples. Distinguish the ideal expectation from stochastic colony variation and retain seed and run identity for reproducibility where the model uses them. The activity explains a modeled classroom procedure and its controls; a result here does not establish that every real bacterial strain, plasmid, or preparation has the same efficiency or induction behavior.

A reference case from this course

The specified preparation combines 250 µL, 10 µL, and 250 µL for a total of 510.000 µL. That total is the basis for the plated-fraction calculation in the course protocol. Keep the actual plated volume separately; the total preparation volume is not itself a colony count or a mass of plasmid DNA.

Keep the investigation reproducible

Before changing the setup, write a prediction that names the measured quantity and the expected direction of change. Retain the original trial as a reference. Record the apparatus conditions, units, and whether you used Ideal or Real lab mode. If the selected activity includes seeded variation, keep the seed and run identity with the result so another comparison does not silently mix different conditions.

Separate the observation from its explanation. A reading or a counted object belongs in the evidence; the relationship you use to interpret it belongs in the reasoning. When a result differs from the reference case, check the settings and measurement procedure before deciding that the model relationship has failed. Describe a specific source of uncertainty and where it enters your calculation. Finish with a claim supported by the recorded comparison, and identify an additional trial that could distinguish your explanation from an alternative.

Continue the comparison

Compare molecular structure in DNA Extraction & Structure and expression mechanisms in From Gene to Protein. Distinguish evidence that genetic material is present from evidence that its encoded product is expressed under a selected condition.