Analysis of Lambda DNA by Gel Electrophoresis

Summary and Results 

Figure 1

Our gel successfully separated DNA fragments creating unique banding patterns for each restriction enzyme used. Fig 1 illustrates our final stained gel showing separation of DNA fragments and digital analysis of distance traveled on left.  We used the HindiIII bands (bottom well) as a molecular

weight ruler or marker as we knew the size of these fragments.  We then estimated the length of unknown DNA band sizes by constructing a a standard curve( figure 2) based upon the measurements obtained from the known DNA HindIII bands. Using Excel's trend line function, we found the relationship between fragment size and distance traveled to be

                fragment size in base pairs = 54892e^(-0.172*distance in mm)

This regression line has a high coefficient of determination of 0.9975 (between 0 and 1.0, used to describe how well a regression line fits a set of data).

Figure 2

Procedure

Gels are placed in electrophoresis chamber which is filled with buffer which helps current flow.

DNA digests are loaded into wells at negative end of the gel. 

From left: uncut lamda DNA, Pstl restriction digest, EcoRI restriction digest

HindiIII restriction digest

running the gels

the loading dye moved across the gel and can be observed easily

pouring the staining solution over the gel to help visualize the DNA bands.

destaining the gels before analysis

DNA Extraction Lab

We used strawberries as the source for our nucleic acids. Strawberries yield more DNA than any other fruit because they are octoploid - they have 8 copies of each chromosome. 

we prepared a solution containing detergent which disrupts the phospholipid membrane around the cells and the nucleus. Sodium chloride  disrupts histones that bind DNA. It also helps to 

keep the proteins dissolved in the aqueous layer so they don’t precipitate in the alcohol 

along with the DNA. 

the strawberry was pulverized by smashing it in a plastic bag with our detergent and salt solution to chemically break apart the cells.

 The solution was then filtered to get rid of strawberry skin and remaining chunks of flesh.

We added an equal volume of 70% ethanol. DNA is not soluble in isopropyl alcohol and  causes the DNA to precipitate and clump together into long strands.  These were captured by swirling a stick at the interface between the two layers. The DNA was transfered to a rube containing alcohol.