03 - Sweet Laboratory: Exploring Food Science with Biotechnology
samples can then be loaded with a micropipet or transfer pipet into wells that were created in the gel by a template during casting. The dense samples sink through the buffer and remain in the wells. A direct current power supply is connected to the electrophoresis apparatus and current is applied. Charged molecules in the sample enter the gel matrix. Molecules having a net negative charge migrate towards the positive electrode (anode) while net positively charged molecules migrate towards the negative electrode (cathode). Within a range, the higher the applied voltage, the faster the samples migrate. The buffer serves as a conductor of electricity and to control the pH. The pH is important to the charge and stability of biological molecules. Agarose is a polysaccharide derived from agar. In this experiment, UltraSpec-Agarose™, a mixture of agarose and hydrocolloids which renders the gel to be both clear and resilient, is used. At first glance, an agarose gel appears to be a solid at room temperature. However, on the molecular level, the gel contains microscopic pores which act as a molecular sieve, allowing the different molecules to pass through. Food dyes are composed of ions. When these charged ions are subjected to an electric field, the molecules will migrate toward the electrode of opposite charge. Positively charged mol- ecules will migrate toward the negative electrode, while those with a negative charge will move toward the positive electrode. Small dye fragments move through these holes easily, but large dye fragments have a more difficult time squeezing through the tunnels. Factors such as charge, size and shape, together with buffer conditions, gel concentrations and voltage, affects the mobility of molecules in gels. Because molecules with dissimilar sizes travel at different speeds, they become separated and form discrete “bands” within the gel. After the current is stopped, the bands can be visualized (Figure 2-2). In this experiment, students will extract several different dyes from food source. The dyes will then be analyzed using agarose gel electrophoresis and their rate of migration will be observed and measured.
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Figure 2-2: Overview of agarose gel electrophoresis.
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