# 2.26 Ribonucleic Acid (RNA) Ribonucleic Acid (RNA) is a vital polymer essential for the expression of genetic information. Its structure and function are distinct from , primarily serving as an intermediary in the synthesis of proteins. ## Chemical Composition Like DNA, RNA is a **polymer of nucleotides**. Each nucleotide contains a ribose sugar, a phosphate group, and a nitrogenous base. ## Structure RNA is generally a **single-stranded** molecule. It does not typically form a stable double helix like DNA. **Secondary Structure:** Despite being single-stranded, some regions of an RNA molecule can fold and pair with complementary regions on the same strand, forming localized **double-stranded structures**. ## Synthesis RNA molecules are produced through a process called **transcription**, where a segment of DNA serves as a template. ## Function and Types There are **three major classes** of RNA. Each class plays a specific and crucial role in the process of **protein synthesis**, which occurs in the . * **Messenger RNA (mRNA):** Carries genetic information from DNA to ribosomes. * **Transfer RNA (tRNA):** Transports amino acids to the ribosomes during protein synthesis. It has a characteristic 'clover-leaf' shape. * **Ribosomal RNA (rRNA):** Along with proteins, it makes up the structure of ribosomes. ## Comparison: RNA vs DNA | Feature | RNA | DNA | | :----------------- | :--------------------- | :--------------------- | | **Strandedness** | Single-stranded | Double-stranded | | **Primary Form** | Linear chain | Two chains coiled around each other | | **Secondary Form** | Localized double-stranded regions | Entire molecule is double-stranded | ## Possible Questions and Answers **Q:** What is the primary structural difference between RNA and DNA? **A:** RNA is generally a single-stranded molecule, while DNA is a double-stranded helix. **Q:** How is RNA synthesized in a cell? **A:** RNA is transcribed using a DNA strand as a template. **Q:** What is the collective function of the major classes of RNA? **A:** The three major classes of RNA are all involved in protein synthesis.