The structural differences between DNA and RNA have significant impacts on their respective roles in protein synthesis. DNA's stability and double-stranded nature make it an ideal repository for genetic information. Its structure ensures that the genetic code is maintained accurately over time. DNA serves as a template for the synthesis of mRNA during transcription. In contrast, RNA's structure, specifically its single-stranded nature and the presence of ribose, makes it more versatile and dynamic, suitable for various roles in protein synthesis. mRNA, a type of RNA, carries the genetic information from DNA to the ribosome, where it is translated into proteins. The single-stranded structure of mRNA allows it to temporarily bind to DNA during transcription and to ribosomes during translation. tRNA, another type of RNA, recognizes specific sequences on the mRNA and brings the appropriate amino acids for protein assembly. The structural differences between DNA and RNA are, therefore, integral to their distinct but complementary roles in the process of protein synthesis.

The antiparallel structure of DNA, where one strand runs in a 5' to 3' direction and the other in a 3' to 5' direction, is essential for its function in storing and retrieving genetic information. This orientation is crucial for DNA replication and repair. During replication, DNA polymerase enzymes synthesize new DNA strands by adding nucleotides to the 3' end of the growing strand. The antiparallel structure allows one strand (the leading strand) to be synthesized continuously, while the other strand (the lagging strand) is synthesized in short segments called Okazaki fragments. This ensures efficient and accurate duplication of the DNA. Additionally, the antiparallel arrangement facilitates complementary base pairing, ensuring that each strand serves as a template for the creation of its counterpart. This complementary nature is key to the accurate transmission of genetic information from one generation to the next, as it allows for the preservation of the sequence of bases, which is the fundamental element of genetic coding.

RNA can form double-stranded structures, although these are generally not as extensive or stable as the double helix of DNA. These double-stranded regions occur when RNA folds back on itself, allowing complementary base pairing within the same molecule or between two RNA molecules. These structures are crucial for various RNA functions. In some RNA molecules, such as certain viral genomes and transfer RNAs (tRNAs), double-stranded regions help stabilize the molecule's three-dimensional shape, which is essential for their function. In other instances, double-stranded RNA (dsRNA) plays a role in regulating gene expression. For example, in the process of RNA interference (RNAi), dsRNA is processed into short interfering RNAs (siRNAs) which guide cellular machinery to degrade specific messenger RNA (mRNA) molecules, thus preventing their translation into proteins. This mechanism is important for controlling gene expression and defending against viral infections. Therefore, while less common than in DNA, double-stranded structures in RNA have important roles in RNA stability, function, and regulation of gene expression.

RNA's reduced stability compared to DNA is primarily due to its ribose sugar and single-stranded structure. The ribose in RNA contains a hydroxyl (-OH) group at the 2' carbon, making it more reactive and susceptible to hydrolysis. This chemical instability means RNA is not suitable for long-term genetic storage but is ideal for short-term tasks. This instability is advantageous for RNA's functions, which include acting as a messenger (mRNA) for protein synthesis, a regulator of gene expression, and a participant in various cellular processes. The transient nature of RNA ensures that messages it carries are not permanently stored, allowing for dynamic regulation of gene expression. Furthermore, RNA's single-stranded structure allows it to fold into complex three-dimensional shapes, enabling it to bind to other molecules and participate in various biochemical processes. These include acting as a catalyst in ribosomes (rRNA) and carrying amino acids for protein synthesis (tRNA).

Uracil in RNA replaces thymine, which is found in DNA. This substitution has significant implications for RNA's structure and function. Structurally, uracil is a smaller molecule than thymine, lacking a methyl group present in thymine. This slight difference affects how RNA nucleotides interact with each other and with other molecules. Functionally, the presence of uracil makes RNA more prone to degradation, fitting its role in transient processes like protein synthesis and gene regulation. Uracil's chemical properties also facilitate the formation of temporary hydrogen bonds with adenine during transcription, allowing RNA to easily detach from DNA following the transcription process. Additionally, the incorporation of uracil in RNA instead of thymine is an evolutionary adaptation. It provides a mechanism to distinguish between uracil-containing RNA and thymine-containing DNA, which is important in cellular processes like DNA repair, where enzymes need to differentiate between RNA and DNA.