Name: agarose gel electrophoresis for the separation of dna fragments
Uploaded: 2012-04-20T12:00:00.000+00:00
Duration: 7 min 10 s
Description: Watch this Scientific Journal Video about Agarose Gel Electrophoresis for the Separation of DNA Fragments at JoVE.com

1. Preparation of the Gel
<ol>
	<li>Weigh out the appropriate mass of agarose into an Erlenmeyer flask. Agarose gels are prepared using a w/v percentage solution. The concentration of agarose in a gel will depend on the sizes of the DNA fragments to be separated, with most gels ranging between 0.5%-2%. The volume of the buffer should not be greater than 1/3 of the capacity of the flask.</li>
	<li>Add running buffer to the agarose-containing flask. Swirl to mix. The most common gel running buffers are TAE (40 mM Tris-acetate, 1 mM EDTA) and TBE (45 mM Tris-borate, 1 mM EDTA).</li>
	<li>Melt the agarose/buffer mixture. This is most commonly done by heating in a microwave, but can also be done over a Bunsen flame. At 30 s intervals, remove the flask and swirl the contents to mix well. Repeat until the agarose has completely dissolved.</li>
	<li>Add ethidium bromide (EtBr) to a concentration of 0.5 μg/ml. Alternatively, the gel may also be stained after electrophoresis in running buffer containing 0.5 μg/ml EtBr for 15-30 min, followed by destaining in running buffer for an equal length of time.</li>
</ol>
Note: EtBr is a suspected carcinogen and must be properly disposed of per institution regulations. Gloves should always be worn when handling gels containing EtBr. Alternative dyes for the staining of DNA are available; however EtBr remains the most popular one due to its sensitivity and cost.
<ol start="5">
	<li>Allow the agarose to cool either on the benchtop or by incubation in a 65 °C water bath. Failure to do so will warp the gel tray.</li>
	<li>Place the gel tray into the casting apparatus. Alternatively, one may also tape the open edges of a gel tray to create a mold. Place an appropriate comb into the gel mold to create the wells.</li>
	<li>Pour the molten agarose into the gel mold. Allow the agarose to set at room temperature. Remove the comb and place the gel in the gel box. Alternatively, the gel can also be wrapped in plastic wrap and stored at 4 °C until use (Fig. 1).</li>
</ol>

2. Setting up of Gel Apparatus and Separation of DNA Fragments
<ol>
	<li>Add loading dye to the DNA samples to be separated (Fig. 2). Gel loading dye is typically made at 6X concentration (0.25% bromphenol blue, 0.25% xylene cyanol, 30% glycerol). Loading dye helps to track how far your DNA sample has traveled, and also allows the sample to sink into the gel.</li>
	<li>Program the power supply to desired voltage (1-5V/cm between electrodes).</li>
	<li>Add enough running buffer to cover the surface of the gel. It is important to use the same running buffer as the one used to prepare the gel.</li>
	<li>Attach the leads of the gel box to the power supply. Turn on the power supply and verify that both gel box and power supply are working.</li>
	<li>Remove the lid. Slowly and carefully load the DNA sample(s) into the gel (Fig. 3). An appropriate DNA size marker should always be loaded along with experimental samples.</li>
	<li>Replace the lid to the gel box. The cathode (black leads) should be closer the wells than the anode (red leads). Double check that the electrodes are plugged into the correct slots in the power supply.</li>
	<li>Turn on the power. Run the gel until the dye has migrated to an appropriate distance.</li>
</ol>
3. Observing Separated DNA fragments
<ol>
	<li>When electrophoresis has completed, turn off the power supply and remove the lid of the gel box.</li>
	<li>Remove gel from the gel box. Drain off excess buffer from the surface of the gel. Place the gel tray on paper towels to absorb any extra running buffer.</li>
	<li>Remove the gel from the gel tray and expose the gel to uv light. This is most commonly done using a gel documentation system (Fig. 4). DNA bands should show up as orange fluorescent bands. Take a picture of the gel (Fig. 5).</li>
	<li>Properly dispose of the gel and running buffer per institution regulations.</li>
</ol>
4. Representative Results
Figure 5 represents a typical result after agarose gel electrophoresis of PCR products. After separation, the resulting DNA fragments are visible as clearly defined bands. The DNA standard or ladder should be separated to a degree that allows for the useful determination of the sizes of sample bands. In the example shown, DNA fragments of 765 bp, 880 bp and 1022 bp are separated on a 1.5% agarose gel along with a 2-log DNA ladder.
<img alt="Gel electrophoresis setup, electrophoresis tray, DNA separation method, lab equipment, biology." src="/files/ftp_upload/3923/3923fig1.jpg" data-altupdatedat="1747911167000" data-alt="Figure 1."> 
Figure 1. A solidified agarose gel after removal of the comb.
<img alt="Pipetting samples in microtubes; experiment setup for DNA analysis; electrophoresis preparation." src="/files/ftp_upload/3923/3923fig2.jpg" data-altupdatedat="1747911167000" data-alt="Figure 2."> 
Figure 2. A student adding loading dye to her DNA samples.
<img alt="Gel electrophoresis setup with pipette for DNA separation; experimental molecular biology technique." src="/files/ftp_upload/3923/3923fig3.jpg" data-altupdatedat="1747911167000" data-alt="Figure 3."> 
Figure 3. A student loading the DNA sample into a well in the gel.
<img alt="PCR workstation setup, includes computer and imaging system for DNA analysis, electrophoresis results." src="/files/ftp_upload/3923/3923fig4.jpg" data-altupdatedat="1747911167000" data-alt="Figure 4."> 
Figure 4. An example of a gel documentation system.
<img alt="DNA gel electrophoresis result, band separation, 2-log ladder, fragment size determination." src="/files/ftp_upload/3923/3923fig5.jpg" data-altupdatedat="1747911167000" data-alt="Figure 5."> 
Figure 5. An image of a gel post electrophoresis. EtBr was added to the gel before electrophoresis to a final concentration of 0.5 μg/ml, followed by separation at 100 V for 1 hour. The gel was exposed to uv light and the picture taken with a gel documentation system.

<ol>
	<li>Sambrook, J., Russell, D. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Molecular Cloning. , (2001).</li><li>Kirkpatrick, F. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Overview+of+agarose+gel+properties.">Overview of agarose gel properties.</a> Electrophoresis of large DNA molecules: theory and applications. , 9-22 (1991).</li><li>Helling, R. B., Goodman, H. M., Boyer, H. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+endonuclease+R&#8226;EcoRI+fragments+of+DNA+from+lambdoid+bacteriophages+and+other+viruses+by+agarose-gel+electrophoresis.">Analysis of endonuclease R&#8226;EcoRI fragments of DNA from lambdoid bacteriophages and other viruses by agarose-gel electrophoresis.</a> J. Virol. 14, 1235-1244 (1974).</li><li>Smith, S. B., Aldridge, P. K., Callis, J. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Observation+of+individual+DNA+molecules+undergoing+gel+electrophoresis.">Observation of individual DNA molecules undergoing gel electrophoresis.</a> Science. 243, 203-206 (1989).</li><li>Aaji, C., Borst, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+gel+electrophoresis+of+DNA.">The gel electrophoresis of DNA.</a> Biochim. Biophys. Acta. 269, 192-200 (1972).</li><li>Lai, E., Birren, B. W., Clark, S. M., Simon, M. I., Hood, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pulsed+field+gel+electrophoresis.">Pulsed field gel electrophoresis.</a> Biotechniques. 7, 34-42 (1989).</li><li>Devor, E. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> IDT tutorial: gel electrophoresis. , (2010).</li><li>Serwer, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Agarose+gels:+properties+and+use+for+electrophoresis.">Agarose gels: properties and use for electrophoresis.</a> Electrophoresis. 4, 375-382 (1983).</li><li>Dea, I. C. M., McKinnon, A. A., Rees, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tertiary+and+quaternary+structure+and+aqueous+polysaccharide+systems+which+model+cell+wall+adhesion:+reversible+changes+in+conformation+and+association+if+agarose,+carrageenan+and+galactomannans.">Tertiary and quaternary structure and aqueous polysaccharide systems which model cell wall adhesion: reversible changes in conformation and association if agarose, carrageenan and galactomannans.</a> J. Mol. Biol. 68, 153-172 (1972).</li><li>Sharp, P. A., Sugden, B., Sambrook, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Detection+of+two+restriction+endonuclease+activities+in+H.+parainfluenzae+using+analytical+agarose-ethidium+bromide+electrophoresis.">Detection of two restriction endonuclease activities in H. parainfluenzae using analytical agarose-ethidium bromide electrophoresis.</a> Biochemistry. 12, 3055-3063 (1973).</li></ol>

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Agarose gel electrophoresis has proven to be an efficient and effective way of separating nucleic acids. Agarose's high gel strength allows for the handling of low percentage gels for the separation of large DNA fragments. Molecular sieving is determined by the size of pores generated by the bundles of agarose7 in the gel matrix. In general, the higher the concentration of agarose, the smaller the pore size. Traditional agarose gels are most effective at the separation of DNA fragments between 100 bp and 25 kb. To separate DNA fragments larger than 25 kb, one will need to use pulse field gel electrophoresis6, which involves the application of alternating current from two different directions. In this way larger sized DNA fragments are separated by the speed at which they reorient themselves with the changes in current direction. DNA fragments smaller than 100 bp are more effectively separated using polyacrylamide gel electrophoresis. Unlike agarose gels, the polyacrylamide gel matrix is formed through a free radical driven chemical reaction. These thinner gels are of higher concentration, are run vertically and have better resolution. In modern DNA sequencing capillary electrophoresis is used, whereby capillary tubes are filled with a gel matrix. The use of capillary tubes allows for the application of high voltages, thereby enabling the separation of DNA fragments (and the determination of DNA sequence) quickly.
Agarose can be modified to create low melting agarose through hydroxyethylation. Low melting agarose is generally used when the isolation of separated DNA fragments is desired. Hydroxyethylation reduces the packing density of the agarose bundles, effectively reducing their pore size8. This means that a DNA fragment of the same size will take longer to move through a low melting agarose gel as opposed to a standard agarose gel. Because the bundles associate with one another through non-covalent interactions9, it is possible to re-melt an agarose gel after it has set.
EtBr is the most common reagent used to stain DNA in agarose gels10. When exposed to uv light, electrons in the aromatic ring of the ethidium molecule are activated, which leads to the release of energy (light) as the electrons return to ground state. EtBr works by intercalating itself in the DNA molecule in a concentration dependent manner. This allows for an estimation of the amount of DNA in any particular DNA band based on its intensity. Because of its positive charge, the use of EtBr reduces the DNA migration rate by 15%. EtBr is a suspect mutagen and carcinogen, therefore one must exercise care when handling agarose gels containing it. In addition, EtBr is considered a hazardous waste and must be disposed of appropriately. Alternative stains for DNA in agarose gels include SYBR Gold, SYBR green, Crystal Violet and Methyl Blue. Of these, Methyl Blue and Crystal Violet do not require exposure of the gel to uv light for visualization of DNA bands, thereby reducing the probability of mutation if recovery of the DNA fragment from the gel is desired. However, their sensitivities are lower than that of EtBr. SYBR gold and SYBR green are both highly sensitive, uv dependent dyes with lower toxicity than EtBr, but they are considerably more expensive. Moreover, all of the alternative dyes either cannot be or do not work well when added directly to the gel, therefore the gel will have to be post stained after electrophoresis. Because of cost, ease of use, and sensitivity, EtBr still remains the dye of choice for many researchers. However, in certain situations, such as when hazardous waste disposal is difficult or when young students are performing an experiment, a less toxic dye may be preferred.
Loading dyes used in gel electrophoresis serve three major purposes. First they add density to the sample, allowing it to sink into the gel. Second, the dyes provide color and simplify the loading process. Finally, the dyes move at standard rates through the gel, allowing for the estimation of the distance that DNA fragments have migrated.
The exact sizes of separated DNA fragments can be determined by plotting the log of the molecular weight for the different bands of a DNA standard against the distance traveled by each band. The DNA standard contains a mixture of DNA fragments of pre-determined sizes that can be compared against the unknown DNA samples. It is important to note that different forms of DNA move through the gel at different rates. Supercoiled plasmid DNA, because of its compact conformation, moves through the gel fastest, followed by a linear DNA fragment of the same size, with the open circular form traveling the slowest.
In conclusion, since the adoption of agarose gels in the 1970s for the separation of DNA, it has proven to be one of the most useful and versatile techniques in biological sciences research.

<table><tbody><tr><td>Agarose I</td><td>Amresco</td><td>0710</td><td></td></tr><tr><td>Boric acid</td><td>Sigma-Aldrich</td><td>B7901</td><td></td></tr><tr><td>Bromophenol blue</td><td>Sigma-Aldrich</td><td>B8026</td><td></td></tr><tr><td>EDTA</td><td>Sigma-Aldrich</td><td>E9884</td><td></td></tr><tr><td>Ethidium bromide</td><td>Sigma-Aldrich</td><td>E7637</td><td>Carcinogenic&amp;#8212;needs to be disposed of as hazardous waste</td></tr><tr><td>Glacial acetic acid</td><td>Fisher Scientific</td><td>BP2401-212</td><td>Corrosive</td></tr><tr><td>Glycerol</td><td>Fisher Scientific</td><td>G33-1</td><td></td></tr><tr><td>Xylene cyanol FF</td><td>Sigma-Aldrich</td><td>X4126</td><td></td></tr><tr><td>Tris base</td><td>Sigma-Aldrich</td><td>T1503</td><td></td></tr><tr><td>Investigator/FX gel documentation system</td><td>Fotodyne Incorporated</td><td></td><td></td></tr><tr><td>Owl Easycast B1 mini gel electrophoresis system</td><td>Thermo Fisher Scientific, Inc.</td><td>B1-PTM</td><td></td></tr><tr><td>EPS 301 power supply</td><td>GE Healthcare</td><td>18-1130-01</td><td></td></tr></tbody></table>

agarose gel electrophoresis for the separation of dna fragments

Agarose gel electrophoresis is the most effective way of separating DNA fragments of varying sizes ranging from 100 bp to 25 kb1. Agarose is isolated from the seaweed genera Gelidium and Gracilaria, and consists of repeated agarobiose (L- and D-galactose) subunits2. During gelation, agarose polymers associate non-covalently and form a network of bundles whose pore sizes determine a gel&#39;s molecular sieving properties. The use of agarose gel electrophoresis revolutionized the separation of DNA. Prior to the adoption of agarose gels, DNA was primarily separated using sucrose density gradient centrifugation, which only provided an approximation of size. To separate DNA using agarose gel electrophoresis, the DNA is loaded into pre-cast wells in the gel and a current applied. The phosphate backbone of the DNA (and RNA) molecule is negatively charged, therefore when placed in an electric field, DNA fragments will migrate to the positively charged anode. Because DNA has a uniform mass/charge ratio, DNA molecules are separated by size within an agarose gel in a pattern such that the distance traveled is inversely proportional to the log of its molecular weight3. The leading model for DNA movement through an agarose gel is &#34;biased reptation&#34;, whereby the leading edge moves forward and pulls the rest of the molecule along4. The rate of migration of a DNA molecule through a gel is determined by the following: 1) size of DNA molecule; 2) agarose concentration; 3) DNA conformation5; 4) voltage applied, 5) presence of ethidium bromide, 6) type of agarose and 7) electrophoresis buffer. After separation, the DNA molecules can be visualized under uv light after staining with an appropriate dye. By following this protocol, students should be able to: 
 
1. Understand the mechanism by which DNA fragments are separated within a gel matrix 
2. Understand how conformation of the DNA molecule will determine its mobility through a gel matrix 
3. Identify an agarose solution of appropriate concentration for their needs 
4. Prepare an agarose gel for electrophoresis of DNA samples 
5. Set up the gel electrophoresis apparatus and power supply 
6. Select an appropriate voltage for the separation of DNA fragments 
7. Understand the mechanism by which ethidium bromide allows for the visualization of DNA bands 
8. Determine the sizes of separated DNA fragments 
&#160;

Watch this Scientific Journal Video about Agarose Gel Electrophoresis for the Separation of DNA Fragments at JoVE.com

Agarose Gel Electrophoresis for the Separation of DNA Fragments

A basic protocol for the separation of DNA fragments using agarose gel electrophoresis is described.

Agarose gel electrophoresis is the most effective way of separating DNA fragments of varying sizes ranging from 100 bp to 25 kb1. Agarose is isolated from ...

agarose-gel-electrophoresis-for-the-separation-of-dna-fragments

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763.0K Views.  University of California Los Angeles. A basic protocol for the separation of DNA fragments using agarose gel electrophoresis is described.

Video: Agarose Gel Electrophoresis for the Separation of DNA Fragments

Real-time Tracking of DNA Fragment Separation by Smartphone

Slab gel electrophoresis (SGE) is the most common method for the separation of DNA fragments; thus, it is broadly applied to the field of biology and others. However, the traditional SGE protocol is quite tedious, and the experiment takes a long time. Moreover, the chemical consumption in SGE experiments is very high. This work proposes a simple method for the separation of DNA fragments based on an SGE chip. The chip is made by an engraving machine. Two plastic sheets are used for the excitation and emission wavelengths of the optical signal. The fluorescence signal of the DNA bands is collected by smartphone. To validate this method, 50, 100, and 1,000 bp DNA ladders were separated. The results demonstrate that a DNA ladder smaller than 5,000 bp can be resolved within 12 min and with high resolution when using this method, indicating that it is an ideal substitute for the traditional SGE method.

Traditional slab gel electrophoresis (SGE) experiments require a complicated apparatus and high chemical consumption. This work presents a protocol that describes a low-cost method to separate DNA fragments within a short timeframe.

Slab gel electrophoresis (SGE) is the most common method for the separation of DNA fragments; thus, it is broadly applied to the field of biology and ...

Biochemistry

Electrophoretic Separation of Proteins

Electrophoresis is used to separate complex mixtures of proteins (e.g., from cells, subcellular fractions, column fractions, or immunoprecipitates), to investigate subunit compositions, and to verify homogeneity of protein samples. It can also serve to purify proteins for use in further applications. In polyacrylamide gel electrophoresis, proteins migrate in response to an electrical field through pores in a polyacrylamide gel matrix; pore size decreases with increasing acrylamide concentration. The combination of pore size and protein charge, size, and shape determines the migration rate of the protein. In this unit, the standard Laemmli method is described for discontinuous gel electrophoresis under denaturing conditions, i.e., in the presence of sodium dodecyl sulfate (SDS). 

In this video, we demonstrate a method for electrophoretic separation of proteins using poly-acrylimide gel electrophoresis (PAGE).

Electrophoresis is used to separate complex mixtures of proteins (e.g., from cells, subcellular fractions, column fractions, or immunoprecipitates), to ...

DNA Electrophoresis Using Thiazole Orange Instead of Ethidium Bromide or Alternative Dyes

DNA gel electrophoresis using agarose is a common tool in molecular biology laboratories, allowing separation of DNA fragments by size. After separation, DNA is visualized by staining. This article demonstrates how to use thiazole orange to stain DNA. Thiazole orange compares favorably to common staining methods, in that it is sensitive, inexpensive, excitable with UV or blue light (to prevent sample damage), and safer than ethidium bromide. Labs already equipped to run DNA electrophoresis experiments using ethidium bromide can generally switch dyes with no additional changes to existing protocols, using UV light for detection. Blue-light detection to avoid sample damage can additionally be achieved with a blue-light source and emission filter. Labs already equipped for blue-light detection can simply switch dyes with no additional changes to existing protocols.

Here, we present a protocol to use thiazole orange for the detection of DNA in gel electrophoresis experiments. The use of thiazole orange allows elimination of ethidium bromide, and fluorescence detection can be achieved with either UV or blue light.

DNA gel electrophoresis using agarose is a common tool in molecular biology laboratories, allowing separation of DNA fragments by size. After separation, ...

DNA Gel Electrophoresis

DNA gel electrophoresis is a technique used for the detection and separation of DNA molecules. An electric field is applied to a gel matrix comprised of agarose, and within the gel, charge particles will migrate and separate based on size. The negatively charged phosphates of the DNA backbone cause DNA fragments to move toward the anode - a positively charged electrode.
The video explains the mechanism by which DNA fragments are resolved on an agarose gel, and it provides a step-by-step generalized procedure for how to prepare agarose gels, load DNA samples, run a DNA gel, visualize DNA fragments, and properly dispose of the gel and running buffer after the experiment is concluded.

DNA Gel Electrophoresis: Concept, Procedure, and Applications

DNA gel electrophoresis is a technique used for the detection and separation of DNA molecules. An electric field is applied to a gel matrix comprised of ...

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Separating Protein with SDS-PAGE

Sodium Dodecyl Sulfate Poly-Acrylamide Gel Electrophoresis, or SDS-PAGE, is a widely-used technique for separating mixtures of proteins based on their size and nothing else. SDS, an anionic detergent, is used to produce an even charge across the length of proteins that have been linearized. By first loading them into a gel made of polyacrylamide and then applying an electric field to the gel, SDS-coated proteins are then separated. The electric field acts as the driving force, drawing the SDS coated proteins towards the anode with larger proteins moving more slowly than small proteins. In order to identify proteins by size, protein standards of a known size are loaded along with samples and run under the same conditions.
This video presents an introduction to SDS-PAGE by first explaining the theory behind it and later demonstrating its step-by-step procedure. Various experimental parameters, such as the polyacrylamide concentration and voltage applied to the gel are discussed. Downstream staining methods like Coomassie and silver stains are introduced, and variations of the method, like 2D gel electrophoresis are presented.

Separating Protein with SDS-PAGE: Procedure and Applications

Sodium Dodecyl Sulfate Poly-Acrylamide Gel Electrophoresis, or SDS-PAGE, is a widely-used technique for separating mixtures of proteins based on their ...

Gel Purification

Gel purification is used to recover DNA fragments after electrophoretic separation. DNA recovery from an agarose gel includes three basic steps: binding, washing and eluting from a silica column. DNA is believed to bind to silica in the presence of high salt via a salt bridge. Following binding, DNA is washed of impurities and eluted under low salt conditions disrupting this interaction.
This video goes through a step-by-step, generalized procedure for cutting out a band from the gel, gel solubilization, purification through binding to a silica column, and elution of purified DNA. In addition, the presentation discusses several tips for ensuring successful gel purification, including the importance of running an agarose gel with a marker or ladder that has DNA of known sizes.

Gel Purification: Recovery of DNA Fragments after Electrophoretic Separation

Gel purification is used to recover DNA fragments after electrophoretic separation. DNA recovery from an agarose gel includes three basic steps: binding, ...

DNA Agarose Gel Electrophoresis

Agarose gel electrophoresis is a laboratory technique commonly used to separate DNA fragments by size. However, it can also be used to isolate and purify DNA fragments using a gel extraction protocol.
Gel extraction follows five major steps: running gel electrophoresis to separate fragments, isolating the individual bands, extracting DNA from those bands, and removing the dye and salts from the extracted mixture to obtain pure DNA.
In cloning experiments, both the insert and vector DNA fragments are obtained after digestion with restriction endonucleases. These DNA fragments of varying sizes are mixed with contaminants, such as enzymes, salts, etc., that can inhibit the ligation reaction that follows. Gel extraction is therefore used to obtain pure DNA fragments before ligation.
To set up a gel for extraction, a lower percent (0.7-0.8%) agarose solution is used to ensure efficient migration of the DNA bands. In addition, a wide-combed gel cast is used to obtain thick DNA bands that are easy to isolate. Then, gel electrophoresis is performed at a lower voltage to prevent heating of the gel and damage to the DNA.
Once gel electrophoresis is complete, the ethidium bromide-stained DNA is identified by exposing the gel to long-wavelength UV for a short time. Short exposure to UV radiation prevents damage to DNA. This is followed by cutting out the desired band using a clean razor blade.
The isolated gel slice containing the DNA fragment of interest is then processed through one of the commercially available gel extraction kits. All of these kits follow the same basic principle. First, the agarose gel is dissolved by a buffer solution containing salts, such as sodium iodide. Next, DNA is bound to a column containing an anionic resin and washed a few times with a dilute alcoholic solution to remove impurities. The column is then dried by spinning in a centrifuge. The pure DNA can now be eluted with buffer or deionized water.

Agarose Gel Electrophoresis for Separation of DNA Fragments

Elektroforeza w żelu agarozowym DNA

Agarose gel electrophoresis is a laboratory technique commonly used to separate DNA fragments by size. However, it can also be used to isolate and purify ...

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KEY TERMS AND CONCEPTS

Two-Dimensional Polyacrylamide Gel Electrophoresis: A Separation Technique for Analysis of Proteins in Complex Protein Mixture Based on Charge and Molecular Weight

To begin this procedure, add 250 microliters of a previously prepared protein sample solution to each slot of a 13-centimeter IPG strip holder. Place an 18-centimeter IPG strip, gel-side down, onto each protein sample solution, taking care to avoid bubbles. Then, add 3 to 4 milliliters of mineral oil to cover each IPG strip.
Next, assemble each IPG strip holder into an isoelectric focusing system, with the pointed end on the back plate, and the square end on the front plate. After rehydrating the IPG strips for 18 hours at room temperature, set the IEF parameters on the isoelectric focusing system with a total runtime of 7.5 hours and 36,875 volt hours.
After IEF, take out each IPG strip from the isoelectric focusing system, and remove the excess mineral oil with an insoluble paper towel. Then, wrap each strip in a sheet of plastic wrap, and store at -80 degrees Celsius.
To cast a 12% PAGE gel, add double-distilled water, 1.5 molar Tris-hydrochloric buffer, 40% acrylamide/bisacrylamide stock solution, 10% ammonium persulfate, and TEMED to a beaker. Mix the gel solution gently, taking care to avoid bubbles.
Gently pour the gel solution into a multi-casting chamber, up to the expected gel height of 19 centimeters. Immediately, add about 3 milliliters of double-distilled water to the multi-casting chamber to cover each resolving gel, and allow each gel to polymerize for about one hour.
This step is very important to prepare a high-quality SDS-PAGE gel. An equal volume water must be immediately added on the top of each gel.
Prepare two liters of electrophoresis buffer, then, add the buffer to an electrophoresis separation unit buffer tank.
After removing the focused IPG strips from the freezer, place them in a plastic vessel containing 1 milliliter of reducing equilibrium buffer and a trace of bromophenol blue, and equilibrate them for 10 minutes with gentle rocking. After removing the reducing equilibrium buffer, add 4 milliliters of alkylation equilibrium buffer, and a trace of bromophenol blue to the IPG strips, and equilibrate them for 10 minutes with gentle rocking.
During gel equilibrium, disassemble the multi-casting chamber, and remove the prepared resolving gel cassette. Rinse the gel cassette three times with double-distilled water, then, remove excess water from the gel cassette with an insoluble paper towel, and place it in a gel stander.
Following this, rinse the equilibrated IPG strips with electrophoresis buffer, and remove excess liquid on each IPG strip surface with an insoluble paper towel. Place an IPG strip onto the resolving SDS-PAGE gel, allowing the IPG strip&#39;s plastic side to contact the longer glass plate, with the pointed end to the left.
Now, quickly add 3 to 4 milliliters of hot 1% agarose and SDS electrophoresis buffer, to seal the IPG strip on the top of each SDS-PAGE gel, and place the top side of the IPG strip down on the top of the shorter glass plate, taking care to avoid bubbles.
These steps are very important to seal the IPG strip to an SDS-PAGE gel. The hot agarose solutions must be immediately added, and the IPG strip must be immediately placed into the top of the SDS gel.
After polymerization, insert the assembled gel cassette vertically between the plastic gaskets and a vertical electrophoresis system. Place the top of the gel with the IPG strip next to the cathode. Next, adjust the level of electrophoresis buffer to immerse the gel cassette by adding the appropriate volume of buffer to the electrophoresis system.
Connect and set the power supply in constant voltage mode, and run at 200 volts for about 370 minutes while monitoring the dye. After the run is complete, take the gel cassette out of the electrophoresis system and gently remove the gel from the gel cassette, taking care to avoid tearing the gel.

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Sodium Dodecyl Sulphate Polyacrylamide Gel Electrophoresis for Protein Analysis: A Technique to Separate and Visualize Proteins Based on Molecular Weight

Prepare two separating gels as described in the text manuscript. Pour the gel between the glass plates using a 1-milliliter pipette, ensuring that the upper 2 centimeters are free of the mixture. Add 70% ethanol on top of the separating gel, creating an even interface between the two layers.
Once the separating gels have polymerized, prepare the stacking gels using instructions in the text manuscript. Then, remove the ethanol from the separating gels, and add the stacking gel solution. Carefully insert a comb with the desired number of pockets, without introducing air bubbles, and allow the gel to polymerize for 20 to 30 minutes.
Load 4 microliters of each sample, as well as the protein ladder, into separate wells. Then, run the gel in Tris-Glycine running buffer at 144 volts for 45 minutes at room temperature. Use pre-warmed Fairbanks solution A to stain the gels on a rocker for 30 minutes, and pre-warmed Fairbanks solution D to decolor the gels on a rocker until the desired background is achieved.

Elektroforeza w żelu poliakryloamidowym z dodecylosiarczanem sodu do analizy białek: technika oddzielania i wizualizacji białek na podstawie masy cząsteczkowej

Agarose Gel Electrophoresis of DNA Amplicons Post PCR: A Method to Analyze Products of Multiplex PCR and Evaluate PCR Reaction Success

According to the manufacturer&#39;s recommendations, add agarose gel powder in 1x TBE buffer to reach 1.5 (weight/volume) percent, and heat to dissolve.
Prior to casting, tilt the dissolved gel solution briefly under running water. Add 5 microliters of fluorescent nucleic acid dye per 50 microliters of gel solution, and mix.
Assemble and level the casting tray. Add combs as appropriate for the number of samples. Pour the gel solution into the cast, and wait for it to solidify.
After that, submerge the cast containing the gel in 1x TBE buffer in a gel electrophoresis system. Mix 5 microliters of the PCR products together with 2 microliters of loading dye in new PCR strips. Transfer 5 microliters of the mixtures to the wells in the gel. Save at least one well empty. Add 5 microliters of DNA ladder in the empty well for reference.
Plug in the electrodes and run the gel at 110 volts per 15 centimeters for approximately 1 hour. Use a UV-based gel imaging system to verify the presence of multiple bands representing PCR amplicons.