In human genome project, scientist notices that one strand of the DNA molecule contains 20 thymine (T), 25 cytosine (C), 30 guanine (C) and 22 adenine (A) residues. How many of each of the bases are found in the complete double-stranded molecule?
**Core Concept**
The human genome project involves understanding the structure and composition of DNA, including the base pairing rules: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). The given DNA strand composition can be used to determine the composition of the complementary strand.
**Why the Correct Answer is Right**
Since A pairs with T and G pairs with C, the complementary strand will have 22 A (to pair with 22 T on the other strand, but given 20 T, it means 20 A will pair with 20 T and the rest of the A will pair with the rest of the T, implying an error in the question as it seems to imply 22 A will pair with 20 T which is incorrect, however, considering the base pairing rules for the given quantities: 20 T will pair with 20 A, 25 C will pair with 25 G, and the remaining bases will pair accordingly), 25 G (to pair with 25 C), 30 is incorrectly stated as C when it should be G to maintain the base pairing rule, and 20 T (to pair with 20 A). Thus, for a complete double-stranded molecule, the correct counts should reflect base pairing rules.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect due to misunderstanding of base pairing rules.
**Option B:** Incorrect as it does not follow the base pairing principle correctly.
**Option C:** Incorrect due to the same reasons as above.
**Clinical Pearl / High-Yield Fact**
Remember, in DNA, A always pairs with T, and G always pairs with C. This 1:1 ratio is crucial for understanding genetic material structure and function.
**Correct Answer:** D. 20 A, 30 G, 25 C, 20 T and the complementary strand will have 20 T, 25 G, 30 C, 22 is an error and should be 20 A.