Final answer:
Nucleotides in DNA are linked together by phosphodiester covalent bonds forming the backbone of the molecule and by hydrogen bonds for base pairing between nitrogenous bases, which contribute to the double helix structure.
Step-by-step explanation:
Nucleotides contribute to the DNA structure primarily through covalent bonds and hydrogen bonds. The phosphate of one nucleotide forms a covalent bond with the sugar of the next nucleotide, creating the backbone of the DNA molecule. This type of covalent bond is known as a phosphodiester bond. Additionally, within the DNA double helix, the nitrogenous bases—adenine (A), thymine (T), cytosine (C), and guanine (G)—form hydrogen bonds with each other. Adenine pairs with thymine (A-T) with two hydrogen bonds, and cytosine pairs with guanine (C-G) with three hydrogen bonds. These hydrogen bonds are responsible for the specific base pairing, which is essential for the DNA's double helical structure and genetic information encoding.
In Figure 14.7, there is a representation of the double helix structure of DNA, phosphodiester bonds (solid lines), and the hydrogen bonds (dotted lines) between the nitrogenous bases. The figure also depicts the major and minor grooves of the DNA molecule, which are important binding sites for DNA-binding proteins during transcription and replication.