DNA fragments introduced into an electrophoresis apparatus...

DNA fragments introduced into an electrophoresis apparatus (see Application, page 390 ) generally carry negative charges equivalent to two extra electrons per base pair of nucleotides in the fragment. The table below shows the forces on several DNA fragments in an electrophoresis apparatus, as a function of the number of base pairs. Plot these data, establish a best-fit line, and use the resulting slope to determine the strength of the electric field in the electrophoresis apparatus. $$ \begin{array}{|l|l|l|l|l|l|l|} \hline \text { Base pairs } & 400 & 800 & 1200 & 2000 & 3000 & 5000 \\ \hline \text { Force }(\mathrm{pN}) & 0.235 & 0.472 & 0.724 & 1.15 & 1.65 & 2.87 \\ \hline \end{array} $$

DNA fragments introduced into an electrophoresis apparatus (see Application, page 390 ) generally carry negative charges equivalent to two extra electrons per base pair of nucleotides in the fragment. The table below shows the forces on several DNA fragments in an electrophoresis apparatus, as a function of the number of base pairs. Plot these data, establish a best-fit line, and use the resulting slope to determine the strength of the electric field in the electrophoresis apparatus.
$$
\begin{array}{|l|l|l|l|l|l|l|}
\hline \text { Base pairs } & 400 & 800 & 1200 & 2000 & 3000 & 5000 \\
\hline \text { Force }(\mathrm{pN}) & 0.235 & 0.472 & 0.724 & 1.15 & 1.65 & 2.87 \\
\hline
\end{array}
$$

Key Concepts

Linear Regression Analysis

Linear regression analysis is a statistical method used to model the relationship between two variables by fitting a best-fit line to the data points. In this context, plotting force against the number of base pairs allows for the extraction of a slope, which is directly related to the electric field strength when considering the proportionality between the number of base pairs (and thus charge) and force.

DNA Charge Distribution

DNA molecules carry a negative charge due to the phosphate backbone in their structure. The charge on DNA increases linearly with the number of base pairs, making longer fragments more strongly influenced by an electric field. This property is fundamental in techniques like electrophoresis where separation based on size is required.

Force on Charged Particles

The force experienced by a charged particle in an electric field is given by the product of the particle's charge and the electric field strength. This relationship, expressed as F = qE, is key to understanding how molecules move in an electrophoretic setup and is used to connect experimental data to the underlying field strength.

Electrophoresis

Electrophoresis is a laboratory technique that uses an electric field to move charged molecules, such as DNA, through a medium like a gel. It is commonly used to separate molecules based on size and charge, allowing for analysis and purification in genetic and biochemical studies.

Electric Field

An electric field is a region around charged particles or objects where other charges experience a force. In the context of electrophoresis, the strength of the electric field directly influences the force exerted on charged molecules, determining their migration speed through the medium.

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