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Deoxyribonucleic acid (DNA) extraction is a crucial process for isolating DNA from cell nuclei. This process involves various steps, including alkaline lysis and DNA purification. Alkaline lysis is commonly used to purify plasmid DNA. Purification is typically carried out using the phenol-chloroform method due to its safety and efficiency. Polymerase Chain Reaction (PCR) is a technique that requires a nuclease-free environment and precise protocol execution, involving denaturation, annealing, and extension steps. Agarose gel electrophoresis is employed to separate DNA molecules based on size, with factors such as agarose concentration, running buffer, voltage, and staining method affecting the migration velocity of DNA fragments (Elkins, 2012; Turner, 2005; Linacre & Tobe, 2013; Maddocks & Jenkins, 2016; Kieleczawa, 2005; Pelt-verkuil, Belkum & Hays, 2008; Walker & Rapley, 2009; Lottspeich & Engels, 2018).
Plasmid DNA extraction was performed as follows:
coli culture was transferred to a microcentrifuge tube and centrifuged at maximum speed for 60 seconds.
This step was repeated with an additional 1 ml of the culture into the same tube.
The PCR reaction mixture was prepared by calculating the necessary dilutions of DNA and the amount of components 1, 2, 3, and 5. The reaction mixture was then prepared, and 20 μl of the mixture and the diluted DNA were added to a PCR tube.
The tube was labeled, spun down, and stored in the fridge for later analysis.
The following steps were followed for nucleic acid electrophoresis:
NanoDrop spectrophotometry was used to determine the DNA concentration and purity of samples 1 and 2. The DNA concentration of sample 1 and 2 were 994.0 ng/µl and 904.5 ng/µl, respectively. To achieve the recommended concentration, sample 1 needed a 20x dilution, while sample 2 required an 18x dilution. The A260/A280 ratio for sample 1 was 1.79, and for sample 2, it was 2.04 (Table 1).
Sample | Concentration (ng/µl) | Extracted DNA Yield - A260 (10mm) | Purity (A260/A280) |
---|---|---|---|
Sample 1 | 994.0 ng/µl | 1.79 | |
Sample 2 | 904.5 ng/µl | 2.04 |
The gel electrophoresis results showed that the DNA ladder contained 14 bands with DNA fragment sizes ranging from 10,000 to 250 base pairs. The log of the ladder was calculated, and a linear equation was derived.
Bands | Migration Ladder Bands (cm) | DNA Size (bp) | Log Ladder |
---|---|---|---|
1 | 5.8 | 10,000 | 4 |
2 | 6.1 | 8,000 | 3.903 |
3 | 6.4 | 6,000 | 3.778 |
4 | 6.8 | 5,000 | 3.699 |
5 | 7.2 | 4,000 | 3.602 |
6 | 7.4 | 3,500 | 3.544 |
7 | 7.9 | 3,000 | 3.477 |
8 | 8.2 | 2,500 | 3.398 |
9 | 8.8 | 2,000 | 3.301 |
10 | 9.2 | 1,500 | 3.176 |
11 | 10.2 | 1,000 | 3 |
12 | 10.4 | 750 | 2.875 |
13 | 11.2 | 500 | 2.699 |
14 | 11.9 | 250 | 2.398 |
The linear equation obtained from the log of base pairs vs. migration ladder bands measured in cm was: y = -0.2394x + 5.3553.
The migration distance for PCR products A (number 14) and B (number 15) were 10.6 cm and 10.4 cm, respectively. Using the linear equation, the actual size of the base pairs was calculated (Table 3).
Experimental Sample | Migration PCR Production (cm) | Calculated Y | Antilog Y |
---|---|---|---|
14 | 10.6 | 2.818 | 657.14 |
15 | 10.4 | 2.866 | 733.74 |
Samples 1 and 2 exhibited relatively high purity with A260/A280 ratios of 1.79 and 2.04, respectively, where a ratio of 1.80 indicates good purity. Both samples had DNA concentrations exceeding 50 ng/µl, necessitating dilution with nuclease-free water. Sample 1 required a 20x dilution, while sample 2 needed an 18x dilution. Gel electrophoresis demonstrated a migration pattern, with smaller DNA fragments traveling farther and larger fragments remaining closer to the top of the gel.
The DNA ladder, containing known and standardized base pair sizes, was used as a reference to verify the actual size of DNA fragments. The linear relationship between the log of base pairs and migration distance was established through the log ladder. The linear equation y = -0.2394x + 5.3553 allowed for the calculation of the actual size of base pairs for PCR products A and B.
Possible sources of error in gel electrophoresis include inaccurate measurements using a ruler, variations in print quality affecting the visibility of DNA ladder bands, pipetting errors, and sample contamination during preparation.
The experiment successfully determined the actual size of base pairs in the samples based on DNA ladder migration patterns. Possible errors were identified, including measurement inaccuracies, print quality, pipetting mistakes, and sample contamination.
Lab Report: DNA Extraction and Electrophoresis. (2024, Jan 02). Retrieved from https://studymoose.com/document/lab-report-dna-extraction-and-electrophoresis
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