Final answer:
Hydrogen bonds are what hold the new and old nitrogen bases together in DNA, ensuring correct base pairing between adenine and thymine, as well as cytosine and guanine.
Step-by-step explanation:
The type of bond that keeps the new nitrogen bases attached to the old nitrogen bases in DNA is called a hydrogen bond. These hydrogen bonds are responsible for the specific pairing between nucleotides: adenine (A) always pairs with thymine (T), forming two hydrogen bonds, and cytosine (C) pairs with guanine (G), forming three hydrogen bonds. This complementary base pairing ensures the DNA double helix structure is maintained, with the base pairs forming the 'steps' of the helical 'staircase'.
While hydrogen bonds are individually weak, the collective strength of numerous hydrogen bonds along the length of the DNA molecule contributes to the overall stability of the double helix structure. This bonding mechanism allows for the precise and faithful transmission of genetic information during cellular processes.