Nucleic Acids: Structure and Functions

Nucleic Acids

Nucleic acids are crucial biomolecules involved in storing and expressing genetic information in all cells and viruses. They consist of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

DNA and RNA Structure

Both DNA and RNA are constructed from nucleotides, which are organized in long chains called polynucleotides. Each nucleotide contains a nitrogenous base, a sugar, and a phosphate group. The nitrogen-containing ring structures of nucleotides are called nucleobases, with DNA having adenine (A), guanine (G), cytosine (C), and thymine (T), while RNA substitutes thymine with uracil (U).

Nucleotides create phosphodiester bonds, linking one sugar molecule to another, forming a backbone. These backbones differ between DNA and RNA: DNA uses 2′-deoxyribose, while RNA utilizes ribose. Additionally, the 2′-hydroxyl group present in ribose is absent in 2′-deoxyribose.

Forms of RNA

There are various types of RNA, each with unique functions:

• Messenger RNA (mRNA): Carries genetic information from DNA to ribosomes to produce proteins.
• Transfer RNA (tRNA): Binds to amino acids and brings them to ribosomes during protein synthesis.
• Ribosomal RNA (rRNA): Structural component of ribosomes, which facilitate translation of mRNA into proteins.
• MicroRNA (miRNA) and short interfering RNA (siRNA): Regulate gene expression by binding to mRNA, preventing protein production.

Nucleotide Synthesis

Nucleotides are synthesized from precursors in the cell. For example, the ribose phosphate portion of purine and pyrimidine nucleotides originates from glucose through the pentose phosphate pathway.

The 2′-hydroxyl group in ribose is removed to create deoxyribonucleoside diphosphate, which eventually becomes DNA. To generate deoxyribonucleoside triphosphate, an additional phosphate group from adenosine triphosphate (ATP) is incorporated by a specific enzyme, akin to the creation of RNA from ribonucleoside triphosphate.

Degradation and Salvage Pathways

Normal cellular activity includes continuous RNA production and breakdown. Nucleotides derived from RNA can be recycled through various salvage pathways, preserving existing genetic material.