Final answer:
In a double-stranded DNA molecule with 6.2 kilobase pairs, if thymine is present in 2160 units, then the number of guanine bases will also be 940, following Chargaff's rule of complementary base pairing.
Step-by-step explanation:
The question relates to the structure of DNA and how the amounts of the nucleotide bases adenine (A), thymine (T), guanine (G), and cytosine (C) relate to each other in a linear double-stranded DNA molecule. According to Chargaff's rule, the number of guanine units is equal to the number of cytosine units, and the number of adenine units is equal to the number of thymine units. This pairing occurs because A and T share hydrogen bonds, as do C and G, maintaining the DNA's helical structure.
Given that the DNA in question has 6.2 kilobase pairs and that thymine is present in 2160 units, we can deduce that adenine is also present in 2160 units. Since the amount of guanine must equal the amount of cytosine, and we have the total number of base pairs in the DNA, we can calculate the amount of guanine (and cytosine). The DNA has a total of 6200 base pairs (counting each side of the base pair), so we can subtract twice the amount of adenine (or thymine) to find the amount of guanine (and cytosine).
To find the number of guanine bases:
- Start with the total number of base pairs: 6200.
- Subtract twice the number of thymine bases to account for both adenine and thymine: 6200 - (2 * 2160) = 1880.
- That 1880 number represents both guanine and cytosine bases combined, so half of it will give us the number of guanine bases: 1880 / 2 = 940.
Therefore, the number of guanine bases in this segment of DNA is 940.