16-3TYU - Campbell Biology

Question

In analyzing the number of different bases in a DNA sample, which would be consistent with the base-pairing rules?

 

1. A=G
2. A+G=C+T. 
3. A+T=G+C.
4. A=C.

Step-by-Step Solution

Answer

1. The option “A=G” is false.
2. The option “A+G=C+T” is true.
3. The option “A+T=G+C” is false.
4. The option “A=C” is false.

Step 1: Genetic material and DNA

DNA is a molecule made of two strands, such as a leading strand and a lagging strand. It is otherwise known as a double-helical structure. 

 

In the DNA, the sugar molecules are attached to the nucleic acids’ bases to form nucleotide bases that are continuously connected to form the DNA sequence. 

Step 2: Explanation of option (A)

A=G shows that the number of adenine is equal to the number guanine. In the DNA, the adenine pairs with the thymine bases. 

 

A=G is not correct as per the base-pairing rules. Chargaff rule states there is an equal amount of adenine and thymine present in the DNA.

Therefore, the given statement is false.

Step 3: Explanation of option (B)

A+G=C+T shows the exact base pairings of the DNA. The amount of adenine and guanine equalizes the amount of cytosine and thymine.

 

According to the base-pairing rule, the number of bases present in the DNA sample balances the number of bases such as A and G, C and T.

Therefore, the given statement is true.

Step 4: Explanation of option (C)

A+T=G+C is the wrong base pairing as per the base-pairing rule. The amount of adenine and thymine does not equalize the amount of guanine and cytosine. 

 

The number of bases present in the DNA is not consistent with the A+T=G+C. 

Therefore, the given statement is false.

Step 5: Explanation of option (D)

The adenine does not have an equal number compared to the cytosine. The amount of cytosine equalizes with the guanine, not with the adenine, as per the Chargaff rule.

 

A=C does not give the correct number of bases present in the DNA. 

Therefore, the given statement is false.