Lab #1: DNA Extraction, Spooling and Quantification

1. What is a nucleus?
The nucleus is a membrane-bound organelle in eukaryotic cells that houses the genetic material (DNA). It serves as the control center of the cell, regulating gene expression, replication, and the transfer of genetic information.

2. What does cell lysis mean?
Cell lysis means breaking open the cell membrane and/or cell wall to release the internal contents, including DNA. In your experiment, chemical solutions disrupt the membrane and release DNA from the nucleus.

3. What precipitates the DNA?
DNA is precipitated by cold isopropyl alcohol in the presence of salt. The salt neutralizes the negative charges on the DNA backbone, and since DNA is insoluble in alcohol, it clumps together and precipitates out of solution.

4. What is the function of the DNA Extraction solution?
The DNA extraction (buffer) solution breaks open cells, stabilizes DNA, and helps remove proteins and lipids. It provides the right chemical environment for cell lysis and releases soluble DNA into the solution.

5. Why did the alcohol layer on top of the DNA solution?
Isopropyl alcohol has a lower density than water, so it forms a layer on top of the aqueous DNA solution. At the interface, DNA becomes visible as it precipitates out.

6. What properties of DNA allow spooling?
DNA molecules are long, thread-like, and sticky when precipitated. This allows them to physically wind around (or “spool” onto) a glass rod when stirred.

7. What is the significance of the values and numbers used in the formula to calculate the concentration of DNA?
The formula is:

DNA concentration (µg/mL) = OD260 ​× dilution factor × 50 µg/mL​

  • OD260: absorbance of DNA at 260 nm (nucleic acids strongly absorb UV light here).

  • Dilution factor: accounts for how much the sample was diluted before measurement.

  • 50 µg/mL: a constant showing that an OD260 of 1 corresponds to 50 µg/mL of double-stranded DNA in a 1 cm pathlength cuvette.

Together, these values let you accurately convert spectrophotometer readings into DNA concentration.