Plasmid isolation is an important technique in molecular biology or any kind of genetic editing. It involves amplifying plasmids overnight by transforming them into competent bacterial cells. The desired colonies of these bacteria can then be grown in shaker cultures, at appropriate shaking speed, oxygen availability and temperature. These liquid cultures can then be ultracentrifuged to pellet the bacteria, which are then used for plasmid isolation. The bacteria are first resuspended in a buffer, then lysed, neutralized, purified in a column, eluted, precipitated with ethanol and then resuspended. During plasmid isolation, it is important to lyse cells quickly because lysing bacteria for too long may lead to irreversible denaturing of the plasmid. Usually, alkaline lysis is used for isolation because it is a mild treatment. It isolates plasmid DNA and other cell components such as proteins by breaking cells apart with an alkaline solution. Precipitation removes the proteins, and the plasmid DNA recovers with alcohol precipitation. Resuspension and lysis buffers should be mixed thoroughly in order to prevent the DNA from breaking into smaller fragments. This is because broken gDNA can reanneal and remain in the solution, without binding to the column.
Plasmid isolation is an important technique in molecular biology or any kind of genetic editing. It involves amplifying plasmids overnight by transforming them into competent bacterial cells. The desired colonies of these bacteria can then be grown in shaker cultures, at appropriate shaking speed, oxygen availability and temperature. These liquid cultures can then be ultracentrifuged to pellet the bacteria, which are then used for plasmid isolation. The bacteria are first resuspended in a buffer, then lysed, neutralized, purified in a column, eluted, precipitated with ethanol and then resuspended. During plasmid isolation, it is important to lyse cells quickly because lysing bacteria for too long may lead to irreversible denaturing of the plasmid. Usually, alkaline lysis is used for isolation because it is a mild treatment. It isolates plasmid DNA and other cell components such as proteins by breaking cells apart with an alkaline solution. Precipitation removes the proteins, and the plasmid DNA recovers with alcohol precipitation. Resuspension and lysis buffers should be mixed thoroughly in order to prevent the DNA from breaking into smaller fragments. This is because broken gDNA can reanneal and remain in the solution, without binding to the column.
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When extracting nucleic acids from cell cultures, thorough homogenization of cells via vortexing in lysis buffer is very necessary. Choose the best RNA isolation method keeping in mind the downstream applications, generally, column-based isolations result in clean and concentrated RNA samples. Downstream applications like sequencing and cDNA synthesis require high-quality RNA, always treat the samples with DNases and check their integrity by running a gel.
When extracting nucleic acids from cell cultures, thorough homogenization of cells via vortexing in lysis buffer is very necessary. Choose the best RNA isolation method keeping in mind the downstream applications, generally, column-based isolations result in clean and concentrated RNA samples. Downstream applications like sequencing and cDNA synthesis require high-quality RNA, always treat the samples with DNases and check their integrity by running a gel.
The most widely used method for protein quantification is by spectrophotometry. The concentration of the protein in the samples is measured at an absorbance of 280 nm. The absorbance of the sample protein is then plotted against a standard curve. This method allows for total protein quantification in a sample (cell and tissue extracts). Before analysing the concentration of protein in the sample, it is important to choose the right test method. For high protein concentration samples (above 5 - 160 mg/ml) the best method is to use the Biuret test. For low concentrations samples (between 1 - 2000µg/ml) the best methods are Lowry assay, BCA assay, Bradford assay and coomassie blue (for exact sensitivity of the test kits you use, refer to manufacturer's protocol). If the samples contain detergents like Triton X-100 then BCA assay is the best choice. For samples that have proteins larger than 3 KDa in size Bradford assay is the best choice. Each method has advantages and disadvantages, plan your analysis considering your sample characteristics.
The most widely used method for protein quantification is by spectrophotometry. The concentration of the protein in the samples is measured at an absorbance of 280 nm. The absorbance of the sample protein is then plotted against a standard curve. This method allows for total protein quantification in a sample (cell and tissue extracts). Before analysing the concentration of protein in the sample, it is important to choose the right test method. For high protein concentration samples (above 5 - 160 mg/ml) the best method is to use the Biuret test. For low concentrations samples (between 1 - 2000µg/ml) the best methods are Lowry assay, BCA assay, Bradford assay and coomassie blue (for exact sensitivity of the test kits you use, refer to manufacturer's protocol). If the samples contain detergents like Triton X-100 then BCA assay is the best choice. For samples that have proteins larger than 3 KDa in size Bradford assay is the best choice. Each method has advantages and disadvantages, plan your analysis considering your sample characteristics.
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