Practical 5 - PCR & Restriction Enzymes & Gel Electrophoresis Worksheet

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May 8, 2024

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BIOL1020 Practical 5 Worksheet PCR2 & Restriction Enzymes & Gel Electrophoresis Make sure you show your tutor your completed worksheet before you leave WORKSHEET TASK 1: 1. Based on the taste test, which version(s) of the TAS2R38 gene do you think you have? BOTH ALLELES CUT ONE ALLELE CUT NO ALLELES CUT taster/taster taster/non-taster non-taster/non-taster X 2. Was your digested sample (tube 3) different from the undigested one (tube 2)? WORKSHEET TASK 2: 1. What is a DNA ladder? DNA fragments of known lengths. 2. Explain fully how you use one to determine the size of a DNA fragment in an agarose gel? The DNA ladder will determine the size of fragments through their relative position. Large fragments will be near the bottom, while small fragments will be near the top. 3. Why do some bands in a gel appear brighter than others? They may have different concentrations than others, thus causing un-uniform staining of bands and therefore difference in appearance when light shines through. 4. How would you approximate the amount of DNA in a sample in a gel if you had a reference ladder in an adjacent lane of the gel containing 1.0 µg DNA in each band? The size and brightness of the DNA in the sample will correspond to the 1 µg DNA ladder. Using brightness, the size amount can be approximated through comparison. 5. Complete the table below. DNA ladder Adjacent lane: Band brightness Adjacent lane: Band weight(µg) 1µg DNA Same brightness 1 µg 1µg DNA Half as bright 0.5 µg 1µg DNA Twice as bright 2 µg
Make sure you show your tutor your completed worksheet before you leave WORKSHEET TASK 3: 1. The λ (lambda) linear DNA is 48,502 base pairs long. From the genome map (in the practical manual p48), calculate the lengths of the fragments when cut (digested) with HindIII. 2. If you load a sample containing DNA fragments 564, 2027, 4361 and 6557 base pairs long into an agarose gel, where would those fragment lengths appear within this gel lane (right) relative to the DNA ladder? Why? Because of their size, each fragment would be moving at different speeds and would thus be in different places (as drawn). 3. The gel you ran was made with a 2.5% w/v solution of agarose. How do you think your results would have differed if the gel had been made using a 4% agarose solution? Why? More concentrated gel would make it more difficult for DNA fragments to pass through due to the increased amount of molecules. Thus, the fragments would most likely not travel as far. 4. Which fragment would travel furthest on the gel? Why? The smallest fragment would travel fastest as they can pass through the gel easier. 5. Which direction do the DNA fragments travel in a gel? Why? DNA is negativey charged so it moves towards the positive electrod due to attracted charges.
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