I'm basically confused about the directions of this slide. Can someone help me?

If I am understanding correctly, the first thing they are asking you to do is match nitrogen bases.

Adenine (A) always pairs with thymine (T), and guanine (G) always pairs with cytosine (C).

Then, whichever are the double strands, cut them out and put them into you notebook. (I am not sure where the notebook is, but I am assuming you know)

Then in the speech bubble next to the picture of Chargaff- talk about his rule.

What does the rule mean?

What does the rule explain?

How is the rule demonstrated?

Lastly, finding percents. What percent of the pairs has Adenine in them?

For example:

If I look at this pairing below

A →T

T→ A

G →C

C→ G

50% of the pairs include Adenine.

Hope I helped! Comment if you have questions about my answer :)

If the sequence of nitrogenous bases of a DNA strand is ATCTAGGCCG, the complementary strand would be TAGATCCGGC, with a percentage of guanine 30%, cytosine 30%, adenine 20% and thymine 20%, according to Chargaff's rule.

Explanation:

DNA is made up of sequences of nitrogenous bases, which are adenine (A), guanine (G), thymine (T) and cytosine (C).  The bases of one strand are matched with the bases of another, according to the complementarity of nitrogenous bases, where:

The image shows a DNA chain whose chain is complementary:

DNA Strand given      Complementary Strand

    Adenine                                Thymine

    Thymine                                Adenine

    Cytosine                                Guanine

    Thymine                                Adenine

    Adenine                                Thymine

    Guanine                                 Cytosine

    Guanine                                 Cytosine

    Cytosine                                Guanine

    Cytosine                                Guanine

    Guanine                                 Cytosine

Therefore, in a DNA molecule there is as much adenine as thymine, and an equal amount of cytosine and guanine. In this example there are 4 molecules of adenine, 4 molecules of thymine, 6 guanines and 6 cytosines.

The proportion or percentages of nitrogenous bases can be calculated according to Chargaff's rule.

Chargaff was able to establish that in a DNA molecule the ratio of purine:pyrimidine of 1:1, so there must be the same amount of thymine as adenine and a similar amount of guanine for the cytosine, according to the complementarity of bases.

Taking into account the law of the base pair, if in a DNA chain there is 30% of Adenine, in the molecule there is:

Guanine 30%

Cytosine 30%

Adenine 20%

Thymine 20%

Total 100%