Graphing DNA Concentration Data
I have attached the DNA content and the graph. I just need help with creating the graph!! Here are the instructions:
2. Let’s convert this data into a graph which we will then take a picture of. You may print the graph on the page below or you may use a sheet of graph paper of your own.
If you use blank graph paper, set up your graph as shown below.
3. The graph will need horizontal and vertical axes as shown below. The horizontal axis should be the values you have control over (the independent variable): the concentration of DNA in the tubes. Use the blank box below the horizontal axis to label the axis using the column heading above. Include the units in the box.
4. The vertical axis is labeled with the values over which you have no control (the dependent variable): the Absorbance values. Notice in the table above that the Absorbance values do not have units.
5. On the horizontal axis below, you have 24 squares to distribute 200 μg of DNA over. Place a “200” on the 24th line, just below the axis line. Back up 12 squares and place a “100” on the 12th line. Place the “50” and “20” values appropriately. (Your graph paper make vary from this, adjust your spacing accordingly.)
6. Use 30 of the 31 lines on the vertical axis to place your Absorbance values. Notice that the values do not correspond neatly to the μg values for the known DNA solutions. It is probably better to divide up the 30 vertical lines across 0.5 Absorbance units. Place 0.5 on the 30th line. Then use the numbers 0.4, 0.3, 0.2 and 0.1 spaced evenly down the vertical axis.
7. Now use the table above to plots the points on your graph. Your first point will lie directly above 200 μg on the horizontal axis and across and slightly below the 0.5 Absorbance value on the vertical axis. Remember that your control tube (0.0 μg of DNA with 0.0 Absorbance is a real point and should be plotted.
8. Once you’ve plotted your 5 points, you are ready to draw a line connecting them. (This is when a clear plastic ruler is useful). You want to draw a straight line that comes nearest to all five points. As you draw the line you are producing what is called a “standard curve” and it makes quite a bold statement. It says that you now know what the concentration of DNA is in any tube of interest to you. Your line relates a long sequence of possible Absorbance values to a corresponding long sequence of DNA concentrations.
9. Let’s assume that your own DNA sample is run through the diphenylamine test and it
has a value of 0.21. Without doing any calculations at all, just look at your graph. Go up the vertical axis and find 0.21. Now use the curve (line) you drew to discover what
the DNA concentration was in your tube. (What was it?) Write it in the lower right hand corner of your graph