During the replication of a DNA molecule, separation of the DNA molecule will normally occur when hydrogen bonds are broken between (1) thymine and thymine (2) guanine and ura- cil (3) adenine and cytosine (4) cytosine and guanine

During the replication of a DNA molecule, separation of the DNA molecule will normally occur when hydrogen bonds are broken between (1) thymine and thymine (2) guanine and ura- cil (3) adenine and cytosine (4) cytosine and guanine.

The correct answer is (3) adenine and cytosine.

Explanation:

1. Thymine and thymine: Thymine only pairs with adenine, not with another thymine. Therefore, hydrogen bonds between thymine and thymine are not broken during DNA replication.
2. Guanine and uracil: Uracil is not present in DNA. It is found in RNA instead. Therefore, hydrogen bonds between guanine and uracil are not relevant to DNA replication.
3. Adenine and cytosine: Adenine pairs with thymine, and cytosine pairs with guanine. During DNA replication, the hydrogen bonds between adenine and thymine are broken, as well as the hydrogen bonds between cytosine and guanine. This allows the DNA molecule to separate into two strands.
4. Cytosine and guanine: As mentioned above, hydrogen bonds between cytosine and guanine are broken during DNA replication, but this is not the main reason for the separation of the DNA molecule.