The specific pairing of nitrogenous bases in DNA - adenine with thymine and guanine with cytosine - is fundamental to the processes of replication and transcription. During DNA replication, the enzyme DNA helicase unwinds the double helix, exposing the bases. DNA polymerase then synthesizes a new complementary strand for each original strand by adding nucleotides according to the base pairing rules: A pairs with T, and G pairs with C. This complementary base pairing ensures that each new DNA molecule is an exact copy of the original, preserving the genetic information accurately through generations.

In transcription, a similar principle applies. RNA polymerase synthesizes an RNA strand using one of the DNA strands as a template. The base pairing rules in transcription are slightly different, with uracil (U) in RNA pairing with adenine (A) in DNA, while cytosine (C) still pairs with guanine (G). This complementary base pairing ensures that the genetic information in DNA is accurately transcribed into RNA, which then directs protein synthesis. Thus, the specific pairing of nitrogenous bases is crucial for the fidelity of genetic information transfer, both in the duplication of DNA and in the synthesis of RNA.

Hydrogen bonds play a crucial role in the structure and properties of nucleic acids. In DNA, hydrogen bonds are responsible for the specific pairing between nitrogenous bases: adenine pairs with thymine via two hydrogen bonds, and guanine pairs with cytosine via three hydrogen bonds. These bonds are not as strong as covalent bonds, making them ideal for the temporary binding needed during processes like DNA replication and transcription. The hydrogen bonding in DNA ensures a consistent distance between the two strands of the helix, contributing to the stability of the double helix structure. This stability is vital for DNA's function as a long-term storage of genetic information.

In RNA, hydrogen bonds also play a significant role. Although RNA is primarily single-stranded, regions within the RNA strand can form hydrogen bonds with each other. This intramolecular bonding allows RNA to fold into various three-dimensional shapes, essential for its functions. For example, in tRNA, hydrogen bonding helps create the distinctive cloverleaf structure necessary for its role in protein synthesis. In rRNA, hydrogen bonding contributes to the formation of the complex structure of the ribosome. Thus, hydrogen bonds are key to both the structural integrity and the functional versatility of nucleic acids.

The presence of an OH group at the 2' position of ribose in RNA, as opposed to the H in DNA's deoxyribose, has significant implications for the molecule's function and stability. This OH group makes RNA more chemically reactive and less stable than DNA. Because of this instability, RNA is typically found in shorter lengths compared to DNA. This reactivity and instability are beneficial for RNA's roles in the cell. For instance, the ability of RNA to fold into complex three-dimensional structures is partly due to the presence of this OH group, enabling it to form hydrogen bonds within the same molecule. These structures are essential for the various functions of RNA, including catalyzing biochemical reactions (as seen in ribozymes), binding to other molecules in the cell, and carrying genetic information from DNA to ribosomes for protein synthesis. Therefore, the OH group at the 2' position of ribose is a key factor in enabling the diverse functions of RNA molecules in cells.

Phosphate groups in nucleic acids are pivotal for both structure and function. Structurally, they form part of the sugar-phosphate backbone, linking the sugar of one nucleotide to the sugar of the next via phosphodiester bonds. This linkage creates a stable, repeating backbone that supports the entire nucleic acid structure. Functionally, the negative charge of the phosphate groups imparts an overall negative charge to nucleic acids. This charge is significant for several reasons. First, it influences the interaction of nucleic acids with positively charged ions and proteins, which is crucial in cellular processes like DNA replication and RNA transcription. Second, the negative charge contributes to the solubility of nucleic acids in water, as it promotes interactions with the polar water molecules. Finally, the repulsion between the negatively charged phosphate groups helps to maintain the nucleic acids in their correct three-dimensional structure, which is essential for their biological function.

The sugar-phosphate backbones of DNA and RNA play a critical role in determining the stability and overall molecular shape of these nucleic acids. In both DNA and RNA, the sugar (deoxyribose in DNA and ribose in RNA) and phosphate groups form a strong covalent bond, creating a robust backbone that provides structural support for the entire molecule. This backbone is responsible for the nucleic acid’s overall polarity and directionality, with a 5’ end (bearing a phosphate group) and a 3’ end (bearing a hydroxyl group). In DNA, this backbone contributes to the stability of the double helix structure, where two strands run in opposite directions (antiparallel) and are held together by hydrogen bonds between complementary bases. The rigidity and regularity of the backbone enable the precise twisting of the DNA strands into the helical structure, which is essential for compact storage of genetic information in the nucleus. In RNA, although it is primarily single-stranded, the backbone allows RNA molecules to fold into various three-dimensional shapes, crucial for their diverse functions, such as mRNA's role in conveying genetic information and tRNA's role in protein synthesis. The backbone’s stability and flexibility are therefore key to the diverse structures and functions of DNA and RNA.