Final answer:
A reagent that breaks hydrogen bonds in DNA disrupts its secondary structure, separating the two strands of the double helix into single-stranded DNA.
Step-by-step explanation:
The level of structure in DNA that would be disrupted by a reagent that breaks apart hydrogen bonds is the secondary structure. The secondary structure refers to the specific arrangement of the double helix where two DNA strands are held together by hydrogen bonds between paired bases. When these hydrogen bonds are disrupted, the double helix denatures, resulting in the separation of the two DNA strands into single-stranded DNA (ssDNA).
The hydrogen bonds are critical to the integrity of DNA's double helix and are responsible for the specific pairing between the nitrogenous bases: adenine (A) with thymine (T), and guanine (G) with cytosine (C). Breaking these hydrogen bonds through heat or chemical reagents leads to the process known as denaturation. This is important in many biotechnological applications, where controlled denaturation and renaturation are utilized for procedures such as DNA sequencing and polymerase chain reaction (PCR).