DNA
Deoxyribonucleic acid forms a double helix structure composed of two polynucleotide chains. Each chain contains alternating sugar and phosphate groups creating a backbone. The sugar component is 2-deoxyribose, which distinguishes DNA from RNA that uses ribose. Four nitrogen-containing bases attach to each sugar unit. These bases are cytosine, guanine, adenine, and thymine. Adenine pairs with thymine through two hydrogen bonds. Guanine pairs with cytosine using three hydrogen bonds. This specific pairing creates the rungs of the molecular ladder. The strands run in opposite directions known as antiparallel orientation. One end carries a free hydroxyl group while the other holds a terminal phosphate group. Scientists measure this directionality as five prime to three prime. The molecule coils around itself forming a right-handed spiral. Most DNA exists as B-DNA under physiological conditions inside cells. Some variations include A-DNA or Z-DNA depending on hydration levels. The major groove allows proteins to access base edges easily. The minor groove remains narrower and less accessible for binding interactions.
Cells store genetic information within chromosomes located in the nucleus. Eukaryotic organisms like humans possess approximately six billion base pairs distributed across forty-six chromosomes. Prokaryotes such as bacteria keep their circular DNA in the cytoplasm without a defined nucleus. Before cell division occurs, enzymes replicate the entire genome to ensure daughter cells receive identical instructions. DNA polymerase builds new strands by reading existing templates one nucleotide at a time. The enzyme adds complementary bases following strict pairing rules between adenine and thymine. Another process called transcription copies genes into messenger RNA molecules. Ribosomes then translate these RNA sequences into amino acid chains forming functional proteins. Mitochondria contain their own small circular genomes separate from nuclear DNA. Human mitochondrial DNA contains roughly sixteen thousand five hundred sixty-nine base pairs per molecule. Each mitochondrion typically holds about five copies of this genetic material. An egg cell can contain up to one hundred thousand mitochondria holding millions of genome copies. Telomeres cap chromosome ends preventing damage during replication cycles. These specialized regions consist of repeating TTAGGG sequences forming quadruplex structures. Enzymes called topoisomerases relieve twisting stress introduced during transcription or replication processes.
Friedrich Miescher isolated a microscopic substance from pus on discarded surgical bandages in 1869. He named this material nuclein because it resided within cell nuclei. Albrecht Kossel later identified the non-protein components as nucleic acids in 1878. Phoebus Levene determined the specific building blocks were sugar, phosphate, and four bases by 1909. Nikolai Koltsov proposed that inherited traits traveled via giant hereditary molecules in 1927. Frederick Griffith demonstrated bacterial transformation using Pneumococcus bacteria in 1928. Oswald Avery confirmed DNA carried genetic information alongside colleagues MacLeod and McCarty in 1943. William Astbury produced the first X-ray diffraction patterns showing regular structure in 1937. Raymond Gosling captured Photo 51 at high hydration levels in May 1952 under Rosalind Franklin's supervision. Francis Crick and James Watson used this critical image to build their double helix model. They announced their discovery at The Eagle pub in Cambridge on the 28th of February 1953. Nature published their findings in April 1953 alongside supporting data from Franklin and Wilkins. Linus Pauling had previously proposed an incorrect triple-helix model with phosphates near the axis. Watson, Crick, and Wilkins shared the Nobel Prize in Physiology or Medicine in 1962 after Franklin's death. Scientists concluded in April 2023 that Franklin was an equal contributor to the discovery process.
British geneticist Sir Alec Jeffreys developed DNA profiling techniques in 1984. Police requested his assistance in a UK criminal investigation involving rape-murder suspects in 1986. A suspect confessed to one crime but denied involvement in another similar case three years prior. Jeffreys' testing exonerated the man from both charges revealing cross-contamination issues. Colin Pitchfork became the first person convicted using DNA evidence in the 1988 Enderby murders case. Forensic scientists compare variable sections of repetitive DNA called short tandem repeats between individuals. This method achieves ninety-nine point nine nine percent probability when matching biological parents to children. Blood, semen, skin, saliva, or hair samples provide sufficient material for identification even from minute traces. Environmental DNA concentrations reach eighty-eight micrograms per liter in natural aquatic environments. Researchers use extracellular DNA as survey tools monitoring species presence in water or air. Mass casualty incidents utilize matching procedures to identify victims through family member comparisons. The technique allows re-examination of cases where original trials failed due to insufficient evidence. Strict handling procedures prevent contamination during modern serious crime investigations.
Life may have existed for four billion years before DNA became the primary genetic material. Early organisms likely used RNA molecules capable of both transmitting information and catalyzing reactions. Pyrimidine bases found in meteorites suggest extraterrestrial origins for building blocks like adenine and guanine. Complex organic compounds including uracil formed under conditions mimicking outer space environments. Ancient DNA survives less than one million years in solution before degrading into fragments. Scientists recovered viable bacteria from salt crystals dated two hundred fifty million years old though claims remain controversial. Extinct woolly mammoths provided genomes observable over millions of years allowing direct genome evolution studies. Phylogenetics compares sequences within species to trace population histories across ecological genetics fields. Human mitochondrial DNA contains unique circular structures distinct from nuclear chromosomes. Some viruses use reverse transcriptase enzymes copying RNA back into DNA forms. The transition from RNA world to DNA-based life remains unclear without direct fossil evidence. Modern research suggests ancient genetic systems traded replication accuracy against catalytic efficiency using fewer base types.
Deoxyribozymes discovered in 1994 function as single-stranded DNA catalysts enhancing reaction rates up to ten billion times. These artificial nucleobases include S, B, P, and Z forming Hachimoji DNA analogues. Researchers create self-assembling branched complexes used as structural materials rather than information carriers. Two-dimensional lattices form through tile-based methods or DNA origami techniques. Three-dimensional polyhedra structures template gold nanoparticles and streptavidin proteins for nanoscale engineering. Environmental DNA concentrations reach eighty-eight micrograms per liter in aquatic environments serving as survey tools. Synthetic oligonucleotide ligands called aptamers target specific molecules for biotechnology applications. DNA storage devices offer higher density compared to electronic memory despite slow read-write speeds. String searching algorithms developed for bioinformatics identify homologous sequences locating mutations distinguishing organisms. Data sets representing entire genomes enable complex evolutionary event examination across species boundaries. Chemical modifications like methylation alter gene expression patterns influencing chromatin structure accessibility. Enzymatic processes such as restriction endonucleases cut DNA at specific six-base sequences enabling molecular cloning. The NaA43 DNAzyme demonstrates over ten thousand-fold selectivity for sodium ions within cellular environments.
Up Next
Continue Browsing
Common questions
What is the chemical structure of DNA and how do its components interact?
Deoxyribonucleic acid forms a double helix structure composed of two polynucleotide chains with alternating sugar and phosphate groups creating a backbone. The sugar component 2-deoxyribose distinguishes DNA from RNA that uses ribose while four nitrogen-containing bases attach to each sugar unit. Adenine pairs with thymine through two hydrogen bonds and guanine pairs with cytosine using three hydrogen bonds to create the rungs of the molecular ladder.
When did scientists discover the double helix model of DNA and who announced it first?
Francis Crick and James Watson used Photo 51 captured by Raymond Gosling in May 1952 under Rosalind Franklin's supervision to build their double helix model. They announced their discovery at The Eagle pub in Cambridge on the 28th of February 1953 before Nature published their findings in April 1953 alongside supporting data from Franklin and Wilkins. Scientists concluded in April 2023 that Franklin was an equal contributor to the discovery process after Watson Crick and Wilkins shared the Nobel Prize in Physiology or Medicine in 1962 following her death.
How does DNA profiling work and what is its accuracy rate for matching biological parents to children?
Forensic scientists compare variable sections of repetitive DNA called short tandem repeats between individuals to achieve ninety-nine point nine nine percent probability when matching biological parents to children. Blood semen skin saliva or hair samples provide sufficient material for identification even from minute traces while environmental DNA concentrations reach eighty-eight micrograms per liter in natural aquatic environments. Colin Pitchfork became the first person convicted using DNA evidence in the 1988 Enderby murders case after British geneticist Sir Alec Jeffreys developed DNA profiling techniques in 1984.
What are the differences between nuclear DNA and mitochondrial DNA in human cells?
Eukaryotic organisms like humans possess approximately six billion base pairs distributed across forty-six chromosomes within the nucleus while mitochondria contain their own small circular genomes separate from nuclear DNA. Human mitochondrial DNA contains roughly sixteen thousand five hundred sixty-nine base pairs per molecule with each mitochondrion typically holding about five copies of this genetic material. An egg cell can contain up to one hundred thousand mitochondria holding millions of genome copies which allows researchers to trace population histories across ecological genetics fields through unique circular structures distinct from nuclear chromosomes.
How long does ancient DNA survive before degrading into fragments and what is the oldest viable bacteria recovery date?
Ancient DNA survives less than one million years in solution before degrading into fragments while scientists recovered viable bacteria from salt crystals dated two hundred fifty million years old though claims remain controversial. Extinct woolly mammoths provided genomes observable over millions of years allowing direct genome evolution studies and phylogenetics compares sequences within species to trace population histories across ecological genetics fields. Life may have existed for four billion years before DNA became the primary genetic material as early organisms likely used RNA molecules capable of both transmitting information and catalyzing reactions.