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Chapter 12 : DNA Goes to the Races

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DNA Goes to the Races, Page 1 of 2

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Abstract:

In the laboratory, scientists separate DNA fragments by a process called gel electrophoresis so that they can look at the results of restriction digests. Under normal circumstances, the phosphate groups in the backbone of DNA are negatively charged. In electrical society, opposites do attract, so DNA molecules are very much attracted to anything that is positively charged. The electric field makes the DNA molecules move, but to cause them to separate and be easy to look at later on, the whole process is carried out in a gel. Since the plan for agarose gels is usually to add DNA to them, scientists place a device called a comb in the liquid agarose after it has been poured into the desired dish and let the agarose harden around the comb. When the comb is removed from the hardened agarose gel, a row of holes in the gel remains. For electrophoresis, the entire gel is placed in a tank of buffer. An electric current is applied across the tank so that it flows through the salt water and the gel. All of the DNA in the gel migrates through the gel toward the positive pole, but the gel material makes it more difficult for larger DNA molecules to move than smaller ones. After a time, the electric current is turned off and the entire gel is placed into a DNA staining solution. After being stained, the DNA can be seen.

Citation: Kreuzer H, Massey A. 2008. DNA Goes to the Races, p 190-193. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch12

Key Concept Ranking

Agarose Gel Electrophoresis
0.5678362
DNA Restriction Enzymes
0.44720498
0.5678362
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Figures

Image of Figure 12.1
Figure 12.1

Casting an agarose gel. (A) To make a gel, hot liquid agarose solution is poured into a casting tray (any shallow container) and the comb is put in place. (B) After the agarose cools and hardens, the comb is removed, leaving behind pits in the gel called sample wells. Samples are loaded into the wells prior to electrophoresis.

Citation: Kreuzer H, Massey A. 2008. DNA Goes to the Races, p 190-193. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch12
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Image of Figure 12.2
Figure 12.2

In electrophoresis, the gel is placed in a tank of salt solution, and an electric current is applied. The DNA migrates toward the positive pole.

Citation: Kreuzer H, Massey A. 2008. DNA Goes to the Races, p 190-193. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch12
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Image of Figure 12.3
Figure 12.3

A scientist is using a micropipette to load a DNA sample into an agarose gel. The gel is in an electrophoresis chamber full of buffer. The power supply for the chamber is on the laboratory bench behind the chamber.

Citation: Kreuzer H, Massey A. 2008. DNA Goes to the Races, p 190-193. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch12
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Image of Figure 12.4
Figure 12.4

In electrophoresis races, the small DNA always wins!

Citation: Kreuzer H, Massey A. 2008. DNA Goes to the Races, p 190-193. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch12
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Download as Powerpoint
Image of Figure 12.5
Figure 12.5

Gel electrophoresis is used to separate products of restriction digestion. (A) Restriction map, with fragment sizes in base pairs. (B) View of gel after electrophoresis.

Citation: Kreuzer H, Massey A. 2008. DNA Goes to the Races, p 190-193. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch12
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Download as Powerpoint

References

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