15.2
DNA分离
许多生物技术和研究应用，如分子克隆，都需要从细胞中提取DNA。为了去除和纯化细胞中的DNA，研究人员采用了各种方法提取DNA。虽然不同协议的细节可能有所不同，但一些一般概念是DNA提取过程的基础。
过程
首先，细胞需要裂解，才能将DNA释放到溶液中。细胞可以使用均质机、超声波仪或打珠机等设备进行物理…
DNA extraction is the removal and purification of DNA from cells. First cells are lysed, broken open. Usually through a combination of physical disruption and treatment with chemicals such as detergent which dissolves the cell and nuclear membranes. The content can then float freely into the surrounding solution.
Next DNA must be separated from the other molecules present. Organic solvents such as phenol and chloroform are commonly used to separate nucleic acids from proteins based on their differing solubility.Additionally, proteinase and RNase enzymes can be used to degrade proteins and RNA leaving the DNA intact.
Salt is usually added to the sample which stabilizes the negatively charged phosphate groups in the backbone of the DNA. And after the addition of ice cold alcohol, precipitates the DNA out of the solution.
The white precipitate is collected by spinning it in a centrifuge where it settles to the bottom of the tube. After washing and re-suspending it in a buffer solution, the extracted DNA can finally be used in research or biotechnology applications.
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Q1: What is the first step in DNA extraction?
The first step is cell lysis, which breaks open cells to release DNA into solution. This is accomplished through physical disruption using equipment like homogenizers or sonicators, combined with chemical treatment using detergents that dissolve the lipid-based cell and nuclear membranes. Once cells are lysed, the DNA content floats freely into the surrounding solution for further processing.
Q2: How are proteins separated from DNA during extraction?
Organic solvents such as phenol and chloroform are commonly used to separate DNA from proteins based on their differing solubility. The sample is vortexed with phenol-chloroform and centrifuged to separate aqueous and organic phases. The DNA-containing aqueous phase at the top is pipetted off, leaving proteins in the organic phase below.
Q3: What role do enzymes play in DNA extraction?
Proteinase K and RNase enzymes are added during or after cell lysis to degrade proteins and RNA respectively, leaving DNA intact. These enzymes selectively break down unwanted cellular molecules, improving DNA purity. This enzymatic degradation works alongside physical and chemical separation methods to remove contaminants from the extracted DNA.
Q4: Why is salt added to DNA extraction samples?
Salt is added to stabilize the negatively charged phosphate groups in the DNA backbone, protecting the molecule during extraction. This ionic stabilization prevents DNA degradation and helps maintain its structural integrity throughout the purification process. Salt also assists in the subsequent precipitation step when alcohol is added.
Q5: How does alcohol precipitation isolate DNA from solution?
Ice-cold alcohol, such as ethanol or isopropanol, is added to the sample, causing DNA to form a white, cloudy precipitate. The sample is then centrifuged, causing the DNA precipitate to collect at the bottom as a pellet. This method effectively separates DNA from dissolved salts and other soluble molecules in the aqueous phase.
Q6: What happens after DNA precipitation in the extraction process?
After precipitation, the DNA pellet is washed by removing the liquid, rinsing in alcohol, and centrifuging again. Following the final wash, the pellet is resuspended in a buffer solution, creating a purified DNA solution ready for use in biotechnology applications like polymerase chain reaction and other molecular techniques.
Q7: Why is centrifugation used multiple times during DNA extraction?
Centrifugation is used at multiple stages to separate materials by density. After cell lysis, it sediments cell debris to the bottom. During phenol-chloroform separation, it divides aqueous and organic phases. Finally, it collects the DNA precipitate as a pellet and removes wash solutions. This repeated use ensures efficient separation and purification throughout the extraction process.