Final answer:
Adding NaCl helps stabilize the hydrogen bonds between complementary DNA bases by neutralizing negative charges on the DNA strands, thereby promoting renaturation. This reduces electrostatic repulsion, allowing the strands to reassociate and return to the double helical structure.
Step-by-step explanation:
When double-stranded DNA (dsDNA) is placed into distilled water, it can denature, which means the hydrogen bonds between the complementary bases of the DNA strands are broken, yielding single-stranded DNA (ssDNA). However, adding sodium chloride (NaCl) aids in the renaturation of DNA. The correct answer to why DNA renatures with the addition of NaCl is: B) NaCl stabilizes hydrogen bonds between complementary bases, promoting renaturation.
NaCl contributes to the stabilization of the DNA molecule by neutralizing the negative charges on the phosphate backbone of DNA strands. The negative charges cause electrostatic repulsion between the strands, which can prevent the strands from coming back together, or renaturing, after they have been denatured. By shielding these charges, NaCl decreases the electrostatic repulsion, thus helping the complementary strands to come close enough to reestablish the hydrogen bonds and allowing the DNA to return to its double helix structure.
Therefore, NaCl does not disrupt hydrogen bonds, as suggested in option A, but rather plays a role in ensuring that the DNA strands can reassociate effectively. It is the presence like those from NaCl, that is critical for the reformation of the double helix. Hence, the addition of NaCl after denaturation helps in the renaturation process by stabilizing the hydrogen bonds that form between complementary bases.