How many thymidyl nucleotides are there in a DNA fragment if 18 cytidyl nucleotides are found in it, which is 10% of the total number of nucleotides in this DNA fragment?
1) Find the total number of nucleotides in a given fragment of the DNA molecule:
18 cytidyl nuclerotides correspond to 10%,
x – 100%, x = 180 nucleotides (A + T + G + C).
2) According to Chargaff’s rule: C + G = 10% + 10% = 20% (or 36 nucleotides).
This means that T + A accounts for: 100% – 20% = 80% (40% each) or 72 nucleotides each:
180 – 100%
x – 40%,
x = 72 nucleotides.
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