98 Fun Facts About DNA

What does DNA stand for?

DNA stands for deoxyribonucleic acid; the 'deoxy' refers to its sugar, 2-deoxyribose, which is ribose missing one oxygen atom.

What is the characteristic shape of a DNA molecule?

The double helix looks like a twisted ladder whose rungs are base pairs; Photo 51, an X-ray image from Rosalind Franklin's King's College lab, showed the X-shaped pattern that confirmed it.

Which three components make up a single DNA nucleotide?

The sugars and phosphates alternate to form each strand's backbone, while the bases point inward and pair across the helix.

Which of these nitrogenous bases is found in RNA but is NOT one of DNA's four?

Uracil takes thymine's place in RNA; the two differ only by a single methyl group on the ring.

In a DNA molecule, Adenine (A) always pairs with which other base?

Adenine always pairs with thymine; Erwin Chargaff found in the late 1940s that DNA's amounts of A and T, and of G and C, are always equal, a clue Watson and Crick used.

What is the primary function of DNA in living organisms?

To store and pass on genetic information; some viruses break the rule and use RNA as their genetic material instead.

Which pair published the double-helix model of DNA, using X-ray data from Rosalind Franklin?

James Watson and Francis Crick shared the 1962 Nobel with Maurice Wilkins; Franklin had died in 1958 and could not be nominated.

In what year was the double helix structure of DNA discovered?

The double helix structure of DNA was famously described by James Watson and Francis Crick in a paper published on April 25, 1953.

What is the main difference in the sugar component between DNA and RNA?

The missing hydroxyl group makes DNA far more chemically stable than RNA, which is one reason it serves as the long-term archive.

Unlike DNA, RNA is typically found in what form?

A single RNA strand can still fold back on itself to form short double-stranded hairpins, giving molecules like tRNA their shape.

According to the central dogma of molecular biology, what is the general flow of genetic information?

Information flows DNA → RNA → protein; Francis Crick first stated the idea in 1957, and retroviruses later showed it can also flow from RNA back into DNA.

What is the process by which a cell makes an identical copy of its DNA before dividing?

Replication is semi-conservative: each new double helix keeps one original strand and one freshly built one.

What is the process of synthesizing proteins from an mRNA template called?

Translation is the process where ribosomes in the cytoplasm synthesize proteins after the process of transcription of DNA to RNA.

What is the unit of DNA wound around a core of eight histone proteins called?

A nucleosome wraps about 147 base pairs, nearly two turns of double helix, around eight histones; the beads-on-a-string chain they form is how two metres of DNA fit in each cell.

What type of mutation involves a change in a single nucleotide base in the DNA sequence?

A point mutation alters a single nucleotide; a transition swaps purine for purine (A↔G) or pyrimidine for pyrimidine (C↔T), while a transversion swaps between the two classes.

What are small, circular DNA molecules in bacteria that replicate independently called?

Plasmids are small, extrachromosomal DNA molecules within a cell that are physically separated from chromosomal DNA and can replicate independently, commonly found in bacteria.

Which enzyme relieves the twisting strain that builds up ahead of the replication fork?

Topoisomerases cut and reseal DNA to release the supercoils that build up ahead of the fork; bacterial DNA gyrase is one, and antibiotics such as ciprofloxacin target it.

How many hydrogen bonds hold together an adenine–thymine base pair in DNA?

An adenine–thymine pair is held by two hydrogen bonds, fewer than a guanine–cytosine pair, so DNA rich in A and T melts apart at a lower temperature.

Who first isolated 'nuclein', now known as DNA, from human white blood cells in 1869?

Swiss physiological chemist Friedrich Miescher first identified what he called 'nuclein' in 1869, laying the groundwork for the discovery of DNA.

What is the name for the enzyme that unwinds the DNA double helix during replication?

Helicase enzymes are crucial in DNA replication, as they unwind the double-stranded DNA into two single strands, making them accessible for replication machinery.

What does a 'silent' point mutation refer to?

A silent mutation leaves the encoded amino acid unchanged; because most amino acids are specified by several codons, many third-position (wobble) changes have no effect on the protein.

Which type of RNA carries genetic information from the nucleus to the ribosomes for protein synthesis?

Messenger RNA (mRNA) acts as an intermediary, carrying the transcribed genetic code from DNA in the nucleus to the ribosomes where proteins are synthesized.

What is the primary role of DNA polymerase during DNA replication?

DNA polymerases can only add nucleotides to an existing 3' end, which is why replication needs a short RNA primer to get started.

What is folding DNA into nanoscale shapes using complementary base pairing called?

DNA origami is a technique that uses the specific interactions between complementary base pairs to fold DNA into arbitrary two- and three-dimensional nanoscale shapes.

What are the stretches of DNA that carry the instructions for a protein or an RNA molecule called?

Genes are the DNA stretches that encode a protein or RNA; in humans the protein-coding portion is only about 1–2% of the genome, the rest being regulatory, structural or of unknown function.

How many hydrogen bonds hold together a guanine–cytosine base pair in DNA?

A guanine–cytosine pair is held by three hydrogen bonds, more than an adenine–thymine pair, so GC-rich DNA needs a higher temperature to melt apart into single strands.

What is the process called when RNA is used as a template to synthesize DNA, as retroviruses do?

HIV relies on this step, which is why many antiretroviral drugs are reverse transcriptase inhibitors.

What is the term for the complete set of genetic instructions carried by an organism?

The genome is the complete set of an organism's DNA; the bacterium E. coli carries its whole genome, about 4.6 million base pairs, on a single circular chromosome.

Which type of mutation occurs when a nucleotide substitution results in a premature stop codon?

A nonsense mutation occurs when a point mutation changes a codon that codes for an amino acid into a stop codon, resulting in a truncated protein.

What do you call the DNA-and-histone complex that condenses into chromosomes?

Chromatin is the complex of DNA and proteins, primarily histones, that condenses to form chromosomes in eukaryotic cells.

Which enzyme makes the short RNA primer that starts each new DNA strand?

Primase lays down an RNA primer of about 10 nucleotides because DNA polymerase can only extend an existing 3' end; the primers are later removed and replaced with DNA.

Leonard Adleman's 1994 proof-of-concept DNA computer solved a seven-point instance of what?

Adleman's test-tube experiment found a Hamiltonian path through seven cities, using DNA strands to generate every possible route at once; he is also the 'A' in RSA encryption.

Who coined the term 'nucleic acid' in 1889?

Richard Altmann, a German pathologist, introduced 'nucleic acid' in 1889 after preparing Miescher's nuclein free of protein; the older name faded as the substance's chemistry became clear.

Which mutation type inserts or deletes nucleotides in a number not divisible by three?

A frameshift mutation is an insertion or deletion not divisible by three; because the code is read in triplets, every codon after it is re-grouped and the protein is garbled.

Which enzyme joins DNA fragments, notably Okazaki fragments, during DNA replication?

DNA ligase seals the nicks between Okazaki fragments on the lagging strand, completing the new strand's backbone; it is also the enzyme that glues cut pieces together in genetic engineering.

How many chromosomes does a normal human body cell contain?

Human body cells carry 46 chromosomes in 23 pairs; chimpanzees and gorillas have 48, because two ancestral chromosomes fused to form human chromosome 2.

Which nitrogenous base is a purine?

Guanine, like adenine, is a purine with a fused double ring; cytosine, thymine and uracil are single-ring pyrimidines, and pairing a purine with a pyrimidine keeps the helix a uniform width.

What are the protective caps at the ends of chromosomes that prevent degradation of genetic information?

Telomeres are repetitive nucleotide sequences at each end of a chromosome, which protect the end of the chromosome from deterioration or from fusion with neighboring chromosomes.

Which molecular biology technique uses short DNA primers to amplify a specific segment of DNA?

Polymerase chain reaction (PCR) was invented by Kary Mullis in 1983; it copies a chosen DNA segment through repeated heating and cooling cycles, and Mullis shared the 1993 Nobel Prize in Chemistry for it.

What type of bond links the sugar of one nucleotide to the phosphate of the next in DNA's backbone?

Phosphodiester bonds are strong covalent links; the much weaker hydrogen bonds between the bases are what let the helix unzip.

Which non-coding region of a gene is cut out of messenger RNA during splicing in eukaryotes?

Intron is short for 'intragenic region'; the pieces that survive splicing, the exons, are what get translated.

What is the deliberate alteration of an organism's genes using laboratory technology called?

The first genetically engineered organism was a bacterium in 1973, and insulin made by engineered E. coli reached patients in 1982.

In a eukaryotic cell, where is most of the DNA kept, packed into chromosomes?

The nucleus holds nearly all of it; mitochondria carry a small circular genome of their own, inherited from the mother.

What technique is used to determine the exact order of nucleotide bases in a DNA molecule?

DNA sequencing is the laboratory technique used to determine the precise order of nucleotides (adenine, guanine, cytosine, and thymine) within a DNA molecule.

What is DNA made by splicing together fragments from different organisms, such as a human gene in a bacterium?

Recombinant DNA is how insulin is made today: the human gene goes into bacteria, which churn out the hormone in vats.

Which enzyme copies a DNA strand's sequence into RNA during transcription?

RNA polymerase builds the RNA strand 5' to 3' from a DNA template; eukaryotes use three kinds, with RNA polymerase II transcribing protein-coding genes into mRNA.

Which amino acid does the start codon AUG specify?

AUG codes for methionine and doubles as the start signal, so nearly every newly made protein begins with it; bacteria use a modified form, formylmethionine, to start.

Which human cell type has no nucleus and so carries no nuclear DNA?

Mature red blood cells eject their nucleus before entering the bloodstream, leaving room for haemoglobin; white blood cells keep theirs, which is why forensic DNA from blood comes from them.

What kind of point mutation swaps one amino acid for another in the resulting protein?

A missense mutation causes sickle cell disease: one base change turns a glutamic acid into a valine in haemoglobin.

Who took Photo 51, the famous X-ray diffraction image of DNA, in May 1952?

Gosling was Franklin's PhD student at King's College London. It got its name simply because it was the 51st diffraction photograph he had taken.

In 1869, DNA was first isolated from pus collected from what?

The Swiss physician who found it called the phosphorus-rich substance 'nuclein'. Its genetic role would not be accepted for another 75 years.

Which duo used E. coli's lactose system to show how cells switch enzymes on and off?

The lac operon became the textbook model of gene regulation and earned the French duo a share of the 1965 Nobel.

The international project to sequence all human DNA was declared complete in which year?

It was declared complete on 14 April 2003, two years ahead of schedule, yet covered only about 92% of the sequence; the last gaps were closed years later.

Which UK leader joined Bill Clinton to announce the draft human DNA sequence in 2000?

The joint announcement came on 26 June 2000. A working draft followed in February 2001, with the finished sequence mapped in April 2003.

Craig Venter launched which firm in 1998 to race the publicly funded human DNA project?

Venter bet on shotgun sequencing to move faster than the government effort. The two sides ended up announcing their drafts together.

Roughly how many base pairs make up the human reference genome, the haploid set?

3.1 billion, and each of your cells carries two copies, so about 6.2 billion base pairs in total.

Roughly how many protein-coding genes does the human reference sequence contain?

Early guesses ran past 100,000. The real figure, 19,000 to 20,000, is close to that of a roundworm, which says a lot about how much regulation matters.

Which human chromosome is the smallest, and present in three copies in Down syndrome?

It is both the smallest autosome and the smallest chromosome overall, at about 46.7 million base pairs.

Mitochondrial DNA is normally inherited from which parent?

The mother, because mitochondria travel in the egg cell; 'Mitochondrial Eve' is the woman all living humans trace back to this way.

How many genes does human mitochondrial DNA carry?

Thirteen code for proteins, 22 for tRNAs and 2 for rRNAs, all on a circle of just 16,569 base pairs.

Where was Alec Jeffreys working when he discovered DNA fingerprinting in 1984?

Alec Jeffreys was at the University of Leicester; his 'eureka moment' came on 10 September 1984 from an X-ray film showing family resemblances in his technician's DNA.

Who was the first person convicted of murder using DNA profiling, sentenced in 1988?

The same profiling first cleared an innocent suspect who had confessed. Pitchfork was caught after persuading a colleague to give a blood sample in his place.

Kirk Bloodsworth, the first death-row inmate exonerated by DNA, was convicted where?

Bloodsworth, a former Chesapeake Bay waterman, was convicted in Maryland in 1985 of a Baltimore County child murder, freed in 1993 after DNA testing, and the DNA later identified the real killer.

In which year did Barry Scheck and Peter Neufeld found the Innocence Project?

Scheck and Neufeld founded the Innocence Project in 1992 at Cardozo School of Law in New York; both later joined O. J. Simpson's 'Dream Team' defence, where DNA evidence was front and centre.

Investigators identified the Golden State Killer in 2018 using which genealogy website?

Investigators uploaded a crime-scene profile to GEDmatch, the free open-upload site, and worked back from distant relatives sharing ancestors from the early 1800s to Joseph DeAngelo.

Which US agency created and maintains CODIS, the national DNA database?

The national tier went live in October 1998; the FBI gave its software free to state and local labs to keep everyone on one system.

Kary Mullis invented PCR in 1983 while working as a DNA chemist for which company?

The idea reportedly struck him on a night drive through Mendocino County. Cetus paid him a $10,000 bonus; the patent later sold for $300 million.

Kary Mullis shared the 1993 Nobel Prize in Chemistry for PCR with which scientist?

Smith was honoured for site-directed mutagenesis. Mullis, a keen surfer, was also awarded the Japan Prize that same year.

Frederick Sanger shared his second Chemistry Nobel, in 1980, with Paul Berg and whom?

Walter Gilbert and Sanger were honoured for DNA-sequencing methods; Sanger's first Nobel, in 1958, was for sequencing insulin, making him one of a handful of double laureates in a single category.

The 1958 Meselson–Stahl experiment labelled DNA with a heavy isotope of which element?

E. coli grown on nitrogen-15 then switched to nitrogen-14 produced hybrid-density DNA, confirming that each new molecule keeps one old strand.

The 1952 Hershey–Chase phage experiments are also known by what appliance nickname?

A blender was used to shear phage coats off infected bacteria. Hershey shared the 1969 Nobel with Delbrück and Luria.

In the Hershey–Chase experiment, radioactive sulfur-35 was used to label what?

Sulfur sits in protein but not DNA, while phosphorus-32 tagged the DNA. Only the phosphorus label turned up in the next phage generation.

Avery, MacLeod and McCarty showed DNA is the 'transforming principle' in which year?

Their 1944 paper purified the substance that turned a harmless bacterial strain deadly and showed it was DNA, not protein; Avery was nominated for a Nobel for decades but never won.

Griffith's 1928 transformation experiment in mice used which bacterium?

Griffith used Streptococcus pneumoniae: heat-killed smooth (virulent) cells mixed with live rough (harmless) cells still killed the mice, hinting that something passed between them.

Z-DNA, named for its zigzag backbone, differs from the common B form by winding in which direction?

Left-handed, unlike the right-handed B-DNA; Alexander Rich's lab at MIT solved its crystal structure in 1979.

In B-DNA, roughly how many base pairs make up one full turn of the helix?

About 10.5 base pairs per turn in solution, a rise of roughly 3.4 nanometres per turn, with the whole molecule only 2 nanometres wide.

Most sequence-reading proteins bind B-DNA through which structural feature?

The major groove is wider because the two strands' attachment points are not directly opposite; it exposes more base edges, so most sequence-reading proteins bind there.

Which six-letter repeat does telomerase add to vertebrate chromosome ends?

Telomerase adds TTAGGG repeats using its own built-in RNA template, extending the 3' end that ordinary copying would leave short.

Blackburn and Greider shared the 2009 Nobel for telomerase with which scientist?

Szostak and Blackburn showed that chromosome-end sequences from a pond ciliate could protect artificial minichromosomes inside yeast.

Transposable elements, or 'jumping genes', make up about what share of human DNA?

Transposable elements make up about 45% of human DNA, mostly retrotransposons such as the million-plus Alu copies; by contrast, protein-coding sequence is only around 1 to 2 percent.

Histones are rich in which two positively charged amino acids?

Lysine and arginine carry positive charges that grip DNA's negative phosphate backbone; adding acetyl groups to lysines loosens that grip and opens up the DNA.

The first Denisovan was identified in 2010 from DNA extracted from what kind of remains?

The finger bone, from a juvenile, came from Denisova Cave in Siberia's Altai Mountains, dug up in 2008; its mtDNA revealed an entirely new human group.

Svante Pääbo won the Nobel in Physiology or Medicine for ancient-DNA work in which year?

Pääbo's 2022 prize honoured the founding of paleogenetics; he led the Neanderthal genome sequencing effort at the Max Planck Institute for Evolutionary Anthropology in Leipzig.

Dolly the sheep was cloned from a cell taken from which part of an adult ewe?

The mammary-gland origin is why she was named for Dolly Parton; born 5 July 1996 at the Roslin Institute, she was the first mammal cloned from an adult body cell.

In the acronym CRISPR, what does the 'P' stand for?

The full name is clustered regularly interspaced short palindromic repeats, a bacterial antiviral defence repurposed as molecular scissors.

Reverse transcriptase was discovered in 1970 by David Baltimore and, independently, who?

Temin found it in Rous sarcoma virus at Wisconsin; Baltimore at MIT. The enzyme lets retroviruses such as HIV write RNA back into DNA.

Nirenberg's 1961 poly-U RNA experiment produced a chain of which amino acid?

Poly-U made polyphenylalanine, so UUU codes for phenylalanine, the first word of the genetic code to be read; Nirenberg shared the 1968 Nobel with Khorana and Holley.

The stop signal UAG is nicknamed 'amber' after a surname meaning amber in which language?

Bernstein is German for amber; the name honours Harris Bernstein, a friend of the discoverers, and the other two stop signals were then dubbed ochre and opal to keep the colour theme.

Which physicist founded the RNA Tie Club in 1954 to puzzle out the genetic code?

George Gamow's club had 20 members, one for each amino acid, with Watson and Crick among them; Crick's unpublished 'adaptor hypothesis' of 1955 was written for it.

In which Cambridge pub did Francis Crick announce in 1953 that he and Watson had found 'the secret of life'?

The Eagle, on Bene't Street, bears a plaque marking the lunchtime interruption of 28 February 1953, when Crick walked in and announced the discovery.

James Watson's Nobel medal sold at Christie's in 2014 for roughly how much?

The hammer price was $4.1 million, about $4.8 million with fees; the buyer, Russian billionaire Alisher Usmanov, returned the medal to Watson, who had said he felt like an 'unperson' after his controversial remarks.

Rosalind Franklin died of ovarian cancer in 1958 at what age?

She died the day before she was due to unveil the structure of tobacco mosaic virus in Brussels, four years before the DNA Nobel was awarded.

Maurice Wilkins, who shared the 1962 Nobel for DNA's structure, was born in which country?

Wilkins was born in Pongaroa, New Zealand, in 1916 and moved to England at six; he worked on isotope separation for the Manhattan Project at Berkeley before turning to X-ray studies of DNA.

Who identified deoxyribose as the sugar in DNA in 1929?

Levene also proposed the mistaken 'tetranucleotide hypothesis', which made DNA look too monotonous to carry genetic information.

UV light damages DNA chiefly by forming which kind of cross-link between adjacent bases?

Adjacent thymines fuse into thymine dimers that kink the helix; cells fix them with repair enzymes, and people with xeroderma pigmentosum, who lack that repair, burn after minutes in sunlight.

Who produced the first X-ray diffraction patterns of DNA's regular structure, in 1937?

Working in Leeds, Astbury also popularised the term 'molecular biology'. Franklin's far sharper images came 15 years later.

The 2017 'DNA Fountain' method stored data at what density per gram of DNA?

Yaniv Erlich and Dina Zielinski reached 215 petabytes per gram by borrowing 'fountain codes' from streaming video, packing data close to DNA's theoretical limit.

Who first detected fetal DNA in a pregnant woman's blood plasma in 1997?

Dennis Lo, in Hong Kong, spotted Y-chromosome sequences in the plasma of mothers carrying boys; that cell-free fetal DNA underpins non-invasive prenatal blood tests for Down syndrome.