DNA information and comparisons
| Stands For: | DeoxyriboNucleic Acid |
| Definition: | A nucleic acid that contains the genetic instructions used in the development and functioning of all modern living organisms. DNA is the primary hereditary material that stores the complete genetic blueprint for an organism. |
| Primary Function: | Long-term storage and transmission of genetic information across generations. Serves as the master blueprint for all cellular functions and organismal characteristics. |
| Structure: | Double-stranded helix with antiparallel strands. Sugar-phosphate backbone with nitrogenous bases. Strands held by hydrogen bonds between complementary base pairs. |
| Sugar Component: | 2-deoxyribose (lacks hydroxyl group at 2' carbon). Absence of 2'-OH group makes it more chemically stable. |
| Nitrogenous Bases: | Adenine (A), Thymine (T), Cytosine (C), Guanine (G). Purines: A and G. Pyrimidines: T and C. |
| Base Pairing Rules: | A pairs with T via 2 H-bonds; C pairs with G via 3 H-bonds. Complementary base pairing enables accurate replication and repair. |
| Helix Geometry: | B-form helix (most common): right-handed, ~10.5 bp/turn, 2 nm diameter, major/minor grooves. Can also form A-form and Z-form (left-handed). |
| Types and Variants: | Nuclear DNA (chromosomal), mitochondrial DNA (mtDNA, circular, maternally inherited), chloroplast DNA (cpDNA in plants, circular), plasmids in bacteria. |
| Cellular Location: | Primarily in nucleus (chromatin with histones). Also in mitochondria and chloroplasts (plants) as circular, histone-free molecules. |
| Molecular Size: | Extremely large. Human genome: ~3.2 billion bp/haploid set. Chromosomes: 50-250 million bp. Mitochondrial DNA: ~16,500 bp. |
| Stability: | Highly stable: deoxyribose lacks reactive 2'-OH, double-strand protects bases, smaller grooves limit enzyme access. Stable in alkaline. Can persist thousands of years (ancient DNA). |
| Chemical Reactivity: | Low reactivity. Absence of 2'-OH prevents nucleophilic attack and self-cleavage. Ideal for long-term stable information storage. |
| Lifespan in Cells: | Permanent in living cells (except cell death). Persists entire organism lifespan. In dead organisms, survives extended periods depending on conditions. |
| Replication/Synthesis: | Self-replicates via DNA polymerase. Needs RNA primers (can't start de novo). Semiconservative replication. Extensive proofreading: ~1 error per 10 billion bases. |
| Catalytic Activity: | No natural catalytic activity. Functions only as information storage. Artificial DNAzymes created in labs for research. |
| Damage and Repair: | Damage from UV (thymine dimers), radiation, oxidation, alkylation. Extensive repair mechanisms: base/nucleotide excision, mismatch repair, double-strand break repair. Thymine (vs uracil) detects cytosine deamination. |
| Modifications: | Modified post-synthesis via methylation. Cytosine methylation (5-mC) regulates gene expression, crucial for epigenetic inheritance. Modifications don't change sequence but affect gene expression. |
| Evolutionary Origin: | Evolved after RNA as more stable storage molecule. Transition from RNA to DNA genomes separated information storage (DNA) from catalysis/transfer (RNA/proteins). |
| Modern Applications: | Genetic testing, forensics (fingerprinting), ancestry/paternity, sequencing (human genome), gene therapy, CRISPR editing, synthetic biology, data storage, personalized medicine, GMO crops, DNA vaccines. |
| Key Biological Significance: | Universal genetic material in cellular life. Stability preserves and transmits genetic info across generations. Mutations provide evolution raw material. Revolutionized medicine, forensics, biotech. |