23S+BISC207+Week+4+DNA+Isolation+Question+Set

2 3S BISC207 - Week 4 (Ex. 2) Question Set: D N A Isolation and D N A Structure Instructions: Type your answers directly into this document and change the color/font/bold the text to make your answers stand out. Save the file as a pdf. For Part C (DNA models), insert pictures of pages 13-15 from your lab manual. Make sure the pictures are large enough to be legible! Save your assignment as a PDF and submit it to the appropriate assignment on Canvas, due by 11:59pm, the day after your lab meets. Double check your submission to ensure you uploaded the correct, complete file to the Canvas assignment. You can resubmit the assignment if needed, though the late penalty will apply if you submit after the due date/time. Part A. Isolating DNA 1. Briefly describe the purpose of the following steps/components in the extraction procedure. (2 pts) a. Soap b. Filtering c. Meat tenderizer d. Alcohol 2. Your DNA extraction buffer was a solution of water mixed with soap and sodium chloride. If you accidentally used a buffer solution made of ethanol mixed with soap and sodium chloride, where would your DNA have ended up (assuming you ran the rest of the procedure the same way as you did in lab)? Why? (1.5 pts) 3. DNA dissolves in an aqueous solution. (1.5 pt) a. Which part of the DNA molecule makes it dissolve in water? b. Is that part of the DNA molecule polar or nonpolar? The soap breaks open the cells by disrupting and emulsifying the cell membranes and disrupts nuclear membranes to release chromosomes. The filtering removes most of the large cellular debris such as the cell wall, cell membrane, and organelles. The meat tenderizer contains digestive enzymes that will break apart the histone proteins on the DNA and allow to to be released into a mostly pure form DNA won’t dissolve in the Alcohol and will form clumps which will create distinct layers which will make it easy to extract the DNA. The DNA would have stayed in the filtrate because DNA does not dissolve in ethanol. This is because DNA requires a polar solvent like water in order to dissociate. A) the sugar-phosphate backbone has a negative charge that allows DNA to easily dissolve in water. B) The sugar-phosphate backbone is highly polar.

c. What makes it polar or nonpolar? Part B. Determining the purity of your sample 4. Write the absorbance values for the DNA sample at 260nm and 280nm. Then calculate your A 260 /A 280 ratio. (1 pt) 5. How does your calculated A 260 /A 280 ratio compare to that of a relatively pure sample of DNA (see the lab manual)? What does that suggest about the contents of your sample? (1 pt) 6. What did you use as the “blank” for calibrating the spectrophotometer in this part, and why? If you accidentally used your DNA sample as the blank and then tried to read the absorbance at 260nm and 280nm for the same DNA sample, what absorbance values would you obtain? Why? (1 pt) Part C. Insert pictures of pages 13-15 from the lab manual. Make sure the pictures are large enough to be legible! This section of the assignment is worth 6 points and will be graded full, half, or no credit. Full credit for completing Exercise C in its entirety, including answering questions and labeling diagrams as requested. It is polar because phosphate groups are negatively charged, so they confer with a negative charge to the DNA molecule. 260 nm: 0.622 280 nm: 0.493 0.622/0.493=1.26 A ratio of ~1.8 indicates a pure DNA sample. Since our ratio is 1.26 which is less than 1.8 it indicates that there are impurities in the DNA sample. We used DI water as our blank when calibrating because it will zero out the absorbance of compounds other than the analyze being determined. If we used our DNA as the blank it would add the absorption measurement of the water and the DNA so the absorbance values would be skewed.