Analysing isolation of DNA plasmid and Agragose of gel electophoresis


(a) The aim of this experiment was to successfully isolate a DNA plasmid from E. Coli skin cells (Escherichia coli). We then use commonly performed a method commonly used in biochemistry and molecular biology called agarose gel electrophoresis. This is employed to split up DNA and RNA fragments corresponding to length are being used to estimate the size and demand of the DNA and RNA fragments or even to separate proteins by size.

In this procedure as explained above, we used e. coli as they are plasmid containing cells. These cells were positioned in a buffer and mixed with a remedy of 1% (w/v) SDS (sodium dodecyl sulphate) which was mixed with sodium hydroxide. The alkaline solution (12. 6PH) triggers the molecular weight boosts this causes it to be like chromosomal DNA. Using alkaline lyses' is dependant on differential denaturation of chromosomal and plasmid DNA to be able to separate the two. The dual stranded plasmid and chromosomal DNA is converted to single stranded DNA due to the lyses of the skin cells which solubilises proteins and denatures the DNA.

Subsequent neutralization is potassium acetate allows only covalently sealed DNA plasmid DNA to reanneal and stay solubilized. Chromosomal and plasmid DNA precipitate in a sophisticated created with potassium and SDS which is removed by centrifugation. Protein dodecyl sulphate complexes are precipitated pass away to it being insoluble in water. When centrifugation neutralizes the lysine it produces to a minuscule supernatant small percentage that contains plasmid DNA a network of chromosomal DNA and protein

Plasmid DNA is targeted by from the supernatant by ethanol precipitation. Plasmid DNA isolated by alkaline lyses is ideal for most analyses and cloning techniques without further purification however if the isolated plasmid DNA is sequenced and extra purification step such as phenol extraction can be used.

(b) The purpose of Agarose gel electrophoresis is to analyse the plasmid DNA that was extracted from the procedure before. The approach of electrophoresis is dependant on the fact that DNA is negatively charged at natural pH because of its phosphate backbone. And like any other natural macromolecules can move in a electrical field. The pace of the DNA decreases when its techniques towards opposing poles due to agarose. The agarose gel is a buffer solution this is utilized to maintain the mandatory pH and sodium awareness. The agarose forms gap or wells in the buffer solution and the DNA placed in through the slots to go toward the positive pole. As mentioned before the agarose gel slows down the speed of DNA so the smaller DNA moves faster than the bigger molecules of DNA as the smaller ones fit through the entire easier. This triggers the DNA to be separated by size and can be seen visually. To make the electrophoresis to function and distinct DNA molecules it must contain an electrophoresis chamber. and power supply, combs that happen to be placed in the chamber this is one way wells are developed when agarose is located in the gel, Trays which has a particular gel that will come in many sizes and and also have UV-properties combs which is how wells are created when agarose is put in the gel, Electrophoresis buffer, Loading buffer, that includes a thick consistancy (e. g. glycerol) so the DNA can be easily located in the wells and a couple of tracking dyes, these travel in the gel and help imagine the way the process has been carried out and moniter what lengths electrophoresis undergone. Ethidium bromide, is a dye used to stain the nucleic acids. . Tran illuminator (an ultraviolet light pack), which is utilized to visualize ethidium bromide-stained DNA in gels.

Method for plasmid isolation

1. 5 ml of culture which has E. coli cells comprising the plasmid pUC118 was placed into an Eppendorf tube.

This was then centrifuged at 13000 rpm for two minutes

The liquid within the Eppendorf tube was discarded carefully by using a pipette and then inverting the tube on the test tube to remove remaining drops of the liquid without getting rid of the bacterial pellet

200 micro-liters of solution A was put into the bacterial pellet. This made certain that the suspension is homogenized (mixtures are well separated

400 micro-liters of solution B was then added and put together well these solutions support the SDS and sodium hydroxide. This neutralizes the solutions

300 micro-liters of solution C which provides the potassium acetate which was also combined and then was incubated on snow for 10 minutes

This concoction was the centrifuged at 13000rpm for 5 minutes

750 micro-liters of the supernatant was used in a fresh Eppendorf tube whilst ensuring nothing of the precipitate was interfered with

10 micro-liters if RNAse solution was added to a duplicate tube and called R+

450 micro-liters of isopropanol was added to each test pipe and blended well

This was then centrifuged at 13000rpm for 5 minutes

The supernatants were then carefully removed and the DNA was retained

400 micro-liters of ethanol was added and allowed to stand for a minute it allow the salts to dissolve the water was carefully removed in order not to remove the DNA precipitate.

The test was then permitted to dry out at room temperature

Each pellet was then dissolved in 10 micro-liters of TE buffer

Q1 The viscosity after 400 micro-liters of solution B was added and combined a low viscosity was seen as it experienced a very watery texture.

Q2 there was no viscosity following the copy of 750 micro-liters of supernatant to a fresh eppendorf

(a) Agarose gel electrophoresis

The sample extracted from the experimental process above were then analyzed using the technique of agarose gel electrophoresis

The RNAse cured and untreated plasmids were analyzed.

10 micro-liters of loading buffer was put into 10 micro-liters of DNA for every single sample

The samples filled with DNA blended with loading buffer were then pipetted into the sample wells, and a present-day was applied. This is carried out for 30 minutes

It was clear that the existing was moving as bubbles were seen to be coming from the electrodes.

The negatively priced DNA migrated towards the positive electrode at the distal end, (which is usually coloured red)

It was analyzed that small DNA substances travelled quickly through the gel which exhibited that the task was completed efficiently as the DNA was separated relating to size

Results/ Discussion

(a) Isolation of DNA plasmid

The DNA plasmid was effectively extracted from the E. coli skin cells and then the DNA was the efficiently separated regarding to size utilizing the agarose gel electrophoresis method.

Solution A is made up of 25 mM of Tris-HCL (pH 8. 0)50 EDTA. Tris is a buffering agent this preserves a continuous pH. The EDTA can be used to protect the DNA from DNAses that are degradative enzymes; the EDTA also binds divalent cations that are necessary for DNAse activity. The answer B has SDS which is a detergent and NaOH. This neutralizes the solution, the alkaline concoction also causes the skin cells to rupture and the SDS the lipid membrane is damaged apart and the cellular protein are solubilized, NaOH converts the DNA into a single strands which is brought on by denaturation. The perfect solution is C is made up of potassium acetate (pH 4. 3) the acetic acid neutralizes the pH, allowing the DNA strands to renature. The potassium acetate is added its causes the SDS to precipitate, along with the cellular dust. The E. coli chromosomal DNA is also precipitated. The plasmid DNA remains in the answer. The viscosity of this is very high as they have a very gel like feel.

When the supernatant is positioned in a new eppendorf tube after five minutes of centrifuge this causes the plasmid DNA to split up from the cellular particles and chromosomal DNA in the pellet.

The isopropanol is then added this pulls the plasmid out and triggers it to precipitate nucleic acids. After centrifuge a little white pellet was witnessed at the bottom of the pipe following the supernatant was carefully removed this further purifies the plasmid DNA from pollutants.

400microliters of ethanol was added this cleaned the residual salt and SDS from the DNA.

All these changes that were observed following the addition of these solutions were expected because they are what help us draw out the DNA plasmid for a finish product.

(b) Agarose gel electrophoresis

After placing the DNA plasmid in the wells electrophoresis was carried out. The results were then obtained and noted.

The size of the DNA fragment is set from its electrophoretic flexibility. The DNA fragments of know molecular weight markers are run on the gel and a graph of log MW against migration distance is drawn.

There are three different forms of agarose DNA first there's the available round plasmid DNA this is actually the first band occurring on the picture. The circular plasmid is a double-stranded circular DNA molecule that is nicked in one of the strands to allow the discharge of any super-helical turns present in the molecule. The open up circular plasmid migrates more slowly but surely when compared to a linear or super-coiled molecule of the same size this is due to associated distinctions in conformation, or condition, of the molecules. this is excatly why it's the first band occurring on the picture consequence.

Linear DNA has free ends, either because both strands have been trim, or because the DNA was linear in vivo. The speed of migration for small linear fragments is immediately proportional to the voltage applied at low voltages. At a given, low voltage, the migration rate of small linear DNA fragments is a function of their size. Large linear fragments (over 20kb or so) migrate at a certain set rate no matter length. This is because the molecules 'resperate', with the bulk of the molecule following a leading end through the gel matrix. Limitation digests are frequently used to analyse purified plasmids. These enzymes specifically break the DNA at certain brief sequences. The ensuing linear fragments form 'rings' after gel electrophoresis. It is possible to purify certain fragments by cutting the bands out of the gel and dissolving the gel release a the DNA fragments. This is neither fast nor poor in comparison to the other DNA plasmid.

The super-coiled Plasmid DNA normally occurs naturally, there is certainly super-coiling in DNA only when there's a replication of your DNA plasmid which occurs for a small space of time that is certainly removed by lowering the DNA by specific enzymes, this is part of DNA replication mechinary. This type of DNA plasmid is the most effective as it is the last music group shown from the three this is Because of its limited conformation.

The picture above shows the results from the agarose gel electrophoresis. The lane numbers are designated above the wells. The street before street 1 that is titled "M" is the molecular weight marker.

All three types of plasmid DNA exists in this final result, the open round, the linear and the supercoiled. There can be an extra band of RNA present however not obviously visible this is because the RNA fragments migrated before dye front as diffuse a strap, the ribonuclease eliminates this group, a blue tracking dye cause the dark-colored smudge under the DNA plasmid and beneath that is the barley visable RNA. RNA is very unpredictable under these conditions, therefore RNA can be completely degraded befor the ribonuclease has been added.

It is seen that DNA is present more in one group then another, however the one with the less amount would have a larger fragment. There appears to be logarithmic relationship between your size of the DNA fragment and the length it trips on the gel. A standered curve can be produced if we measure the length the bands in various lanes travelled if the fragment sizes are known. The greater points plotted and the bigger the separation you can find on the gel, the results could be more accurate.


The experimental strategies completed were a success, the DNA plasmid was obtained and the agarose gel electrophoresis resulted with in a clear picture as shown and layed out above, of the DNA being effectively separated.

The uses of purified plasma in DNA research is for molecular cloning.

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