After precipitation, the nucleic acids can then be separated from the rest of the solution by centrifugation. After a further centrifugation step, the ethanol is removed and the nucleic acid pellet is allowed to dry before resuspending in a clean aqueous buffer. First, we need to know why nucleic acids are soluble in water.
Water is a polar molecule — it has a partial negative charge near the oxygen atom due to the unshared pairs of electrons, and partial positive charges near the hydrogen atoms. Because of these charges, polar molecules like DNA or RNA can interact electrostatically with the water molecules, allowing them to easily dissolve in water. Nucleic acids are hydrophilic due to the negatively charged phosphate PO 3 — groups along the sugar-phosphate backbone.
OK, so back to the protocol. The role of salt in the protocol is to neutralize the charges on the sugar-phosphate backbone. A commonly used salt is sodium acetate. The positively charged sodium ions neutralize the negative charge on the PO 3 — groups on the nucleic acids, making the molecule far less hydrophilic and, therefore, much less soluble in water.
Based in San Diego, John Brennan has been writing about science and the environment since Components of Lysis Buffers. Properties of Isopropyl Alcohol. Steps of DNA Transcription. RNA Mutation Vs.
DNA Mutation. The Purpose of the Buffer in Electrophoresis. Examples of Acidic Buffers. Discussion Questions To extract DNA from cells, what must you isolate it from in the case of a plant such as strawberry? What steps did we use to extract the DNA? What is DNA used for when it is extracted? After the cell walls have been disrupted during mechanical mashing of the fruit, the detergent in the shampoo disrupts the cell and nuclear membranes of each cell to release the DNA.
It does this by dissolving lipids and proteins that hold the membranes together. It also causes proteins and carbohydrates to precipitate. They are there to protect the cell from invasion by viruses.
Once the nuclear membrane is destroyed by the soap, the DNA is now susceptible to the DNases and will quickly be degraded. However, these enzymes are temperature sensitive and cooling the solution slows down the process of degradation. Everything except the DNA will dissolve in ethanol. The ethanol pulls water from the DNA molecule so that it then collapses in on itself and precipitates.
The DNA will become visible as white mucous strands that can be spooled with the wooden applicator stick. The colder the ethanol is the greater the amount of DNA that is precipitated. You could try having some of the students use room temperature ethanol and see if the amount of DNA they can spool is the same or less than that for the groups using the ice-cold ethanol. Discussion Questions and Answers To extract DNA from cells, what must you isolate it from in the case of a plant such as strawberry?
All the other parts of the cell - the cell wall, cell membrane, nuclear membrane, mitochondria, vacuoles, endoplasmic reticulum, Golgi apparatus, lysosomes, etc. First we broke apart the cell walls by physically squishing the fruit. The chemical detergent process broke down the cell walls, cell membranes and nuclear membranes.
0コメント