Science Lab Report
BACKGROUND CONTEXT (so you understand what the experiment is about):
This lab is about bacterial transformation — a type of horizontal gene transfer (HGT) where bacteria take up foreign DNA from their environment. In our case, we introduced a plasmid called pAMP into E. coli bacteria. A plasmid is a small, circular piece of DNA that exists separately from a bacterium's main chromosome. The pAMP plasmid carries a gene that makes bacteria resistant to the antibiotic ampicillin.
The transformation process works like this:
1. E. coli cells are made "competent" (able to take up DNA) by chilling them on ice
2. The plasmid is added to the cells
3. The cells are briefly heat-shocked (placed in a 42°C water bath for a short time) — this temporarily disrupts the cell membrane and allows the plasmid to enter
4. Cells are returned to ice to reseal the membrane
5. Cells recover in LB broth (a nutrient-rich liquid), then are plated onto agar plates
6. Plates are incubated overnight at 37°C and colonies are counted the next week
To check if transformation worked, we use two types of plates:
- LB plates: regular nutrient plates — ALL bacteria grow here (transformed or not)
- LB/Amp plates: plates containing ampicillin — ONLY bacteria that successfully took up the pAMP plasmid (and gained resistance) can grow here
Plates are labeled (+) if pAMP was added to that tube, and (−) if no pAMP was added (negative control).
Transformation efficiency = number of antibiotic-resistant colonies per microgram (µg) of plasmid DNA used. It tells us how successful the transformation was.
MY EXPERIMENT:
Instead of just doing the standard protocol, my group tested whether heat-shock TIME affects transformation efficiency. We compared 60 seconds vs. 90 seconds of heat shock, both at 42°C.
FORMAT REQUIREMENTS:
- 12 pt. font, 1.5 line spacing
- Single document
- Must include these four sections: Introduction & Hypothesis, Experimental Setup, Results, Hypothesis Evaluation
INTRODUCTION & HYPOTHESIS:
- Background concepts to weave in: plasmids, HGT, transformation, ampicillin resistance
- Research question: How does changing heat-shock time affect the transformation efficiency of E. coli with the pAMP plasmid?
- Hypothesis: If heat-shock time is changed from the standard condition, then transformation efficiency will change — an optimal heat-shock time will produce the highest number of ampicillin-resistant colonies, while times that are too short OR too long will reduce efficiency
- Null hypothesis: Changing heat-shock time will not affect transformation efficiency
EXPERIMENTAL SETUP:
- Independent variable: heat-shock time (60 sec vs. 90 sec)
- Dependent variable: number of colonies on LB/Amp plates (CFU) and transformation efficiency
- Controls: negative control tube (no pAMP added); results also compared to standard technique lab data
- Materials used: E. coli competent cells, pAMP plasmid DNA (concentration: 0.005 µg/µL), ice bucket, 42°C water bath, LB broth, LB agar plates, LB/Amp agar plates, micropipettes + sterile tips, sterile cell spreader, 37°C incubator, marker and timer
- Protocol:
1. Labeled microtubes: 60s, 90s, and negative control
2. Added equal volumes of competent E. coli cells to each tube, kept on ice
3. Added 10 µL of pAMP to the 60s and 90s tubes; added nothing (no DNA) to the negative control
4. Gently mixed and kept all tubes on ice for 10 minutes
5. Heat-shocked each tube at 42°C for its assigned time (60s or 90s exactly)
6. Immediately returned all tubes to ice for 2 minutes
7. Added equal volumes of LB broth to each tube for recovery
8. Incubated all tubes at 37°C for 30–45 minutes
9. Plated 50 µL from each tube onto both LB and LB/Amp plates
10. Incubated plates overnight at 37°C 11. Counted colonies one week later
RESULTS:
60 sec heat shock:
- LB(−): ~3,100 colonies (normal bacterial growth, no plasmid) -
LB(+): ~850 colonies (bacteria with pAMP on regular plate)
- LB/Amp(+): 2,976 colonies ← KEY RESULT (transformed, ampicillin-resistant colonies)
- Transformation efficiency: ~3.69 × 10⁵ colonies/µg pAMP
90 sec heat shock:
- LB(−): 2,834 colonies
- LB(+): 776 colonies
- LB/Amp(+): 0 colonies ← KEY RESULT (no transformation occurred)
- Transformation efficiency: 0
How transformation efficiency was calculated:
- Total pAMP added: 10 µL × 0.005 µg/µL = 0.05 µg
- Total suspension volume: ~310 µL (cells + pAMP + LB broth)
- pAMP in the 50 µL plated: 0.05 µg × (50 ÷ 310) ≈ 0.00806 µg
- TE = colony count ÷ 0.00806 µg = ~3.69 × 10⁵ colonies/µg
HYPOTHESIS EVALUATION:
This section MUST include both direct implications and broad implications.
- The results support the hypothesis — heat-shock time clearly and dramatically affected transformation efficiency
- 60s produced nearly 3,000 transformed colonies; 90s produced zero
- Direct implication: 90 seconds of heat shock was too long — prolonged heat exposure likely damaged the cell membrane or heat-sensitive proteins involved in DNA uptake, preventing transformation entirely. 60 seconds appears to be closer to the optimal duration.
- Broad implication: Heat-shock duration is an extremely sensitive and critical variable in bacterial transformation protocols. Even a 30-second difference completely eliminated transformation success. This has major implications for molecular biology, genetic engineering, and any biotechnology application that relies on bacterial transformation (e.g., producing insulin, cloning genes, making recombinant proteins).
- The null hypothesis is rejected — heat-shock time does affect transformation efficiency.
IMPORTANT NOTES:
- This is an individual graded assignment — write it in a natural, authentic first-person student voice
- It will be submitted through TurnItIn with AI detection — do NOT make it sound AI-generated
- Keep it concise — this is a SHORT summary, not a full lab report
- If you include any scientific references, they MUST be real, verifiable, published papers — no made-up citations. I need to be able to look them up myself before I submit.