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Archive for the ‘Bio-Rad Tutorial’ Category

What the heck is a coefficient of variation?

 :: Posted by American Biotechnologist on 06-25-2012

Statistics is probably one of the most important tools you will use in your research career. Stats have the ability to turn your seemingly beautiful data into a pile of useless junk, or to convert questionable data into an award winning publication.

Like many molecular biologists, I am statistically challenged. I’ve tried and tried again to learn the meaning behind important terms such a “p-value,” “ANOVA test” and “correlation coefficient” all to no avail. I am a stats flunkie. When I asked my supervisor about my learning disability he told me that I am a molecular biologist and that really there is not hope.

The best we can shoot for is p<0.05 and call it significant.

For many years, I was resigned to the fact that I’d never understand stats and that’s why the position of in-house statistician existed. To help, (if not to make fun of), people like me. Fortunately, there is new hope. Bio-Rad Laboratories has now produced a series of video tutorials geared towards helping those who have less fortunate statistical skills.

In the video below, Bio-Rad experts explain how to calculate a coefficient of variation. I found the video to be pretty clear and it has somewhat clarified this murky term for me. What about you?

Keeping it constant: A lesson in protein transfer

 :: Posted by American Biotechnologist on 05-22-2012

Power supplies that are used for electrophoresis hold one parameter constant (either voltage, current, or power). The PowerPac™ HC and PowerPac Universal power supplies also have an automatic crossover capability that allows the power supply to switch over to a variable parameter if a set output limit is reached. This helps prevent damage to the transfer cell.
During transfer, if the resistance in the system decreases as a result of Joule heating, the consequences are different and depend on which parameter is held constant.

Transfers Under Constant Voltage
If the voltage is held constant throughout a transfer, the current in most transfer systems increases as the resistance drops due to heating (the exception is most semi-dry systems, where current actually drops as a result of buffer depletion). Therefore, the overall power increases during transfer, and more heating occurs. Despite the increased risk of heating, a constant voltage ensures that field strength remains constant, providing the most efficient transfer possible for tank blotting methods. Use of the cooling elements available with the various tank blotting systems should prevent problems with heating.

Transfers Under Constant Current
If the current is held constant during a run, a decrease in resistance results in a decrease in voltage and power over time. Though heating is minimized, proteins are transferred more slowly due to decreased field strength.

Transfers Under Constant Power
If the power is held constant during a transfer, changes in resistance result in increases in current, but to a lesser degree than when voltage is held constant. Constant power is an alternative to constant current for regulating heat production during transfer.

The above information was adapted from Bio-Rad’s protein blotting guide. For more great information, be sure to download the Protein Blotting Guide from Bio-Rad Laboratories.

Running a great 2D gel from start to finish

 :: Posted by American Biotechnologist on 04-02-2012

Great proteomics tutorial from Bio-Rad Laboratories.

Introduction to High Resolution Melt Analysis

 :: Posted by American Biotechnologist on 03-05-2012

In our last post we told you about how Bio-Rad Laboratories very own Sean Taylor and Francisco Bizouarn were crowned the kings of MIQE. Today we’d like to bring you another classic from his majesty Frank. In the slideshow below, you will learn the basics of High Resolution Melt Analysis (HRM), applications, important considerations, assay design and optimization and analysis software. Enjoy. And all hail the king!

A primer on fluorescence detection

 :: Posted by American Biotechnologist on 01-31-2012

Yesterday we told you about how to get more data from your western blots by utilizing multiplex fluorescent detection. Today, we will provide you with a primer on fluorescent detection taken from the Bio-Rad Laboratories Protein Blotting Guide.

In fluorescence, a high-energy photon (ℎVex) excites a fluorophore, causing it to leave the ground state (S0) and enter a higher energy state (S’1). Some of this energy dissipates, allowing the fluorophore to enter a relaxed excited state (S1). A photon of light is emitted (ℎVem), returning the fluorophore to the ground state. The emitted photon is of a lower energy
(longer wavelength) due to the dissipation of energy while in the excited state.

When using fluorescence detection, consider the following optical characteristics of the fluorophores to optimize the signal:

  • Quantum yield — efficiency of photon emission after absorption of a photon. Processes that return the fluorophore to the ground state but do not result in the emission of a fluorescence photon lower the quantum yield.Fluorop hores with higher quantum yields are generally brighter

  • Extinction coefficient — measure of how well a fluorophore absorbs light at a specific wavelength. Since absorbance depends on path length and concentration (Beer’s Law), the extinction coefficient is usually expressed in cm–1 M–1. As with quantum yield, fluorophores with higher extinction coefficients are usually brighter

  • Stokes shift — difference in the maximum excitation and emission wavelengths of a fluorophore. Since some energy is dissipated while the fluorophore is in the excited state, emitted photons are of lower energy (longer wavelength) than the light used for excitation. Larger Stokes shifts minimize overlap between the excitation and emission wavelengths, increasing the detected signal

  • Excitation and emission spectra — excitation spectra are plots of the fluorescence intensity of a fluorophore over the range of excitation wavelengths; emission spectra show the emission wavelengths of the fluorescing molecule. Choose fluorophores that can be excited by the light source in the imager and that have emission spectra that can be captured by the instrument. When performing multiplex western blots, choose fluorophores with minimally overlapping spectra to avoid channel crosstalk
  • For more information be sure to download the Protein Blotting Guide from Bio-Rad Laboratories.