Final answer:
The correct bonds that link the two strands of DNA together are hydrogen bonds. These bonds occur between the nitrogenous bases, forming the internal rungs of the DNA double helix, while the sugar-phosphate backbones of each strand are connected by phosphodiester bonds.
Step-by-step explanation:
The bonds linking the two DNA strands together are known as hydrogen bonds. These hydrogen bonds form between the nitrogenous bases of the two DNA strands. According to the Watson-Crick model of DNA structure, each base pairs with its complementary base (adenine with thymine and guanine with cytosine) through specific hydrogen bonding patterns. Adenine and thymine form two hydrogen bonds, while cytosine and guanine form three. It is this base pairing, held together by hydrogen bonds, that forms the rungs of the DNA 'ladder' and keeps the double helix structure stable.
The sugar-phosphate backbone of each DNA strand is held together by phosphodiester bonds, which occur as part of the sugar-phosphate backbone and play a crucial role in giving DNA its structural integrity. These bonds are distinct from the hydrogen bonds that connect the two DNA strands. Figuratively shown in various figures, hydrogen bonds connect the base pairs internally, leading to the iconic double-helix formation of DNA.