RNA information and comparisons
| Stands For: | RiboNucleic Acid |
| Definition: | A versatile nucleic acid that plays multiple roles in coding, decoding, regulation, and expression of genes. RNA acts as the intermediary between genetic information and functional proteins, while also performing catalytic and regulatory functions. |
| Primary Function: | Transfers genetic info from DNA to ribosomes (mRNA), decodes instructions (tRNA), forms ribosome catalytic core (rRNA), regulates gene expression (miRNA, siRNA, lncRNA). |
| Structure: | Usually single-stranded but folds into complex 3D structures (hairpins, loops, pseudoknots). Structural versatility enables catalytic and regulatory functions. |
| Sugar Component: | Ribose (has hydroxyl group at 2' carbon). The 2'-OH group makes RNA more reactive but enables catalytic activity. |
| Nitrogenous Bases: | Adenine (A), Uracil (U), Cytosine (C), Guanine (G). Purines: A and G. Pyrimidines: U and C. Uracil replaces thymine, lacks a methyl group. |
| Base Pairing Rules: | In double-stranded regions: A pairs with U via 2 H-bonds; C pairs with G via 3 H-bonds. Can also form non-Watson-Crick base pairs in complex structures. |
| Helix Geometry: | A-form helix: right-handed, ~11 bp/turn, wider and shorter than B-form, deeper major groove. More compact and stable for single strands forming local double-stranded regions. |
| Types and Variants: | mRNA, tRNA, rRNA, miRNA, siRNA, lncRNA, snRNA, piRNA, circRNA. |
| Cellular Location: | Synthesized in nucleus, transported to cytoplasm. Found in cytoplasm, ribosomes, nucleus, and various compartments depending on RNA type and function. |
| Molecular Size: | Much smaller than genomic DNA. mRNA: hundreds to tens of thousands of nucleotides. tRNA: 76-90 nt. rRNA: ~120 nt (5S) to ~5,000 nt (28S). miRNA: 21-23 nt. |
| Stability: | Less stable: 2'-OH causes base-catalyzed hydrolysis, single-strand exposes bases, wider grooves allow RNase access. Unstable in alkaline. Instability allows rapid cellular response. |
| Chemical Reactivity: | Higher reactivity. 2'-OH acts as nucleophile, attacking phosphodiester bond, causing self-cleavage. Enables ribozyme catalysis but requires continuous synthesis. |
| Lifespan in Cells: | Temporary and dynamic. Continuously synthesized, used, degraded. Half-life: minutes (some mRNAs) to days (rRNA in non-dividing cells). Rapid turnover enables quick cellular adjustment. |
| Replication/Synthesis: | Synthesized from DNA via RNA polymerase. Can initiate de novo (no primers needed). Not self-replicating except RNA viruses. Lower fidelity: ~1 error per 10,000-100,000 bases. |
| Catalytic Activity: | Many RNAs are catalytic (ribozymes). Examples: ribosomal peptidyl transferase, self-splicing introns, RNase P. Dual role as info carrier and catalyst supports RNA World hypothesis. |
| Damage and Repair: | More resistant to UV thymine dimers (uses uracil). Susceptible to oxidation and hydrolysis. Damaged RNA degraded and replaced, not repaired. Uracil vs thymine is metabolically efficient since RNA is disposable. |
| Modifications: | 170+ post-transcriptional modifications: pseudouridine, m6A, m5C, inosine, others. Regulate stability, localization, translation efficiency. Modified nucleosides in tRNA essential for codon recognition. |
| Evolutionary Origin: | RNA World hypothesis: RNA predated DNA and proteins, serving as genetic material and catalyst. Supported by RNA catalysis, ribosome role, RNA nucleotides as DNA precursors. Some viruses still use RNA genomes. |
| Modern Applications: | mRNA vaccines (COVID-19), RNAi therapeutics (siRNA drugs like patisiran), antisense oligonucleotides, CRISPR guide RNAs, RNA aptamers, RNA-seq, single-cell sequencing. |
| Key Biological Significance: | Bridges genetic info and functional proteins (Central Dogma: DNA→RNA→Protein). Regulates nearly all gene expression. Discovery of catalytic/regulatory RNAs transformed understanding of regulation and life origins. |