Name: how dna structure was discovered
Uploaded: 2023-04-30T10:29:48.000Z
Duration: 1 min 7 s
Channel: JoVE

K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Biology

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms- Structures and Processes

LS.Bio.1.5

The DNA Helix

Desoxyribonukleinsäure oder DNA besteht aus zwei Polynukleotidketten.
Jede dieser Ketten besteht aus vier Arten von Nukleotiduntereinheiten.
Jedes Nukleotid besteht aus einer einzelnen Phosphatgruppe und einer stickstoffhaltigen Base – Adenin, A, Cytosin, C, Guanin, G oder Thymin, T, die an einen Desoxyribosezucker gebunden sind.
Diese Anordnung bildet das Zucker-Phosphat-Rückgrat der DNA-Struktur.
Entlang des Rückgrats jedes Strangs verbinden Phosphodiesterbindungen kovalent das dritte Kohlenstoffatom eines Zuckers mit dem fünften Kohlenstoffatom des nächsten Zuckermoleküls in der Kette.
In den gegenüberliegenden antiparallelen Strängen ist jede Base eindeutig gepaart, C mit G und A mit T, aufgrund der Unterschiede in der Anzahl der Wasserstoffbrückenbindungen, die sich zwischen ihnen bilden.
Diese chemische Polarität sorgt für eine effiziente Packung, indem die beiden Stränge umeinander gewickelt werden, um eine 3-D-Doppelhelix mit zehn Basenpaaren bei jeder vollen Umdrehung zu bilden.

die dna-helix

Desoxyribonukleinsäure oder DNA ist das genetische Material, das bei allen Organismen und den meisten Viren für die Weitergabe von Merkmalen von Generation zu Generation verantwortlich ist. DNA besteht aus zwei Nukleotidsträngen, die sich umeinander winden und eine federartige Struktur bilden, die als Doppelhelix bezeichnet wird. Allerdings ist die Doppelhelix nicht perfekt symmetrisch. Stattdessen kommt es regelmäßig zu Rillen in der Struktur. Die Hauptfurche entsteht dort, wo die Zucker-Phosphat-Grundgerüste relativ weit voneinander entfernt sind. Dieser Raum ermöglicht den Zugang zu DNA-bindenden Proteinen, wie zum Beispiel Transkriptionsfaktoren. Im Gegensatz dazu entsteht die kleine Furche dort, wo die Zucker-Phosphat-Grundgerüste dicht beieinander liegen. Relativ wenige Proteine binden über die kleine Furche an die DNA.

Die Entdeckung der DNA-Struktur: Eine kurze Geschichte

Die Entdeckung der DNA-Struktur erfolgte schrittweise über fast ein Jahrhundert und stellt eine der berühmtesten und fesselndsten Geschichten in der Geschichte der Wissenschaft dar.

Alles begann im Jahr 1869, als der Schweizer Wissenschaftler Friedrich Miescher eine Substanz entdeckte, die er „Nuclein“ nannte. Bei der Proteingewinnung aus weißen Blutkörperchen fand Miescher eine unerwartete Substanz mit relativ hohem Phosphorgehalt. Er wusste nicht, was es war, aber er vermutete, dass es biologisch wichtig sein könnte. Miescher hatte recht, aber es dauerte Jahrzehnte, bis die wissenschaftliche Gemeinschaft seine Erkenntnisse voll und ganz würdigte.

Die nächste entscheidende Entdeckung machte der russische Biochemiker Phoebus Levene. Im Jahr 1919 schlug Levene vor, dass Nuklein, das damals als Nukleinsäure bekannt war, aus Molekülketten bestehe, die er Polynukleotide nannte. Levenes Vorschlag ging auf seine Forschungen zu Hefe zurück, bei denen er herausfand, dass einzelne Nukleotide aus einer Phosphatgruppe, einem Zucker und einer stickstoffhaltigen Base bestehen. Obwohl Levenes Polynukleotidmodell in vielerlei Hinsicht korrekt war, war noch unklar, wie die Basen im DNA-Molekül angeordnet waren.

Der österreichische Biochemiker Erwin Chargaff erweiterte die Arbeit von Levene. Ende der 1940er Jahre machte Chargaff eine wichtige Entdeckung: Die Menge an Adenin in der DNA entspricht immer ungefähr der Menge an Thymin, und die Menge an Guanin entspricht immer ungefähr der Menge an Cytosin. Dieses Muster wurde als Chargaff-Regel bekannt und war ein wichtiger Beweis, der die endgültige Aufklärung der DNA-Struktur ermöglichte.

In den frühen 1950er Jahren lieferten sich der amerikanische Biologe James Watson und der englische Physiker Francis Crick einen Wettlauf mit ihrem Hauptkonkurrenten, dem Amerikaner Linus Pauling, um die dreidimensionale Struktur der DNA zu entdecken. Aufbauend auf der Arbeit von Chargaff nutzten sie Kenntnisse in Physik, Mathematik und Chemie, um physikalische DNA-Modelle zu konstruieren. Doch sie blieben erfolglos, bis sie ein entscheidendes Datenelement erhielten: ein Röntgenfoto der DNA, das deren Doppelhelixstruktur in präzisen Details erkennen ließ. Bei diesem Foto handelte es sich um unveröffentlichte Daten der Physikerin Rosalind Franklin, die ohne Franklins Wissen an Watson und Crick weitergegeben wurden. Watson und Crick veröffentlichten 1953 ihre Beschreibung der DNA-Struktur und gewannen zusammen mit Maurice Wilkins (einem Mitarbeiter von Franklin) 1962 für diese Entdeckung den Nobelpreis für Physiologie oder Medizin. Leider starb Franklin 1958 und hatte daher keinen Anspruch auf einen Nobelpreis.

Die DNA-Helix

Desoxyribonukleinsäure oder DNA ist das genetische Material, das für die Weitergabe von Merkmalen von Generation zu Generation in allen Organismen und den meisten Viren verantwortlich ist. DNS...

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Cells, Genomes, and Evolution

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KEY TERMS AND CONCEPTS

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how dna structure was discovered

DNA is the genetic material that passes traits from one generation to the next in organisms and most viruses. It is made of two strands of nucleotides that twist into a spring-like double helix. The shape is not perfectly even. It also has repeating grooves called the major groove and the minor groove.

The major groove forms where the sugar-phosphate backbones are farther apart. This wider space gives DNA-binding proteins, including transcription factors, better access to the bases. The minor groove forms where the backbones are closer together. Relatively few proteins bind to DNA through the minor groove.

The story of DNA structure unfolded over nearly a century. It began in 1869, when Swiss scientist Friedrich Miescher found a phosphorus-rich substance in white blood cells and called it nuclein. He did not know what it was, but he suspected it had biological importance. Later work showed that his idea was right.

In 1919, Russian biochemist Phoebus Levene proposed that nucleic acid was made of chains of molecules called polynucleotides. His yeast studies showed that each nucleotide contains a phosphate group, a sugar, and a nitrogen-containing base. This model was useful, but it still did not explain how the bases were arranged in DNA. In the late 1940s, Erwin Chargaff added a key clue by showing that adenine is roughly equal to thymine and guanine is roughly equal to cytosine.

That evidence helped James Watson and Francis Crick build their DNA models in the early 1950s. They were competing with Linus Pauling and used ideas from physics, mathematics, and chemistry. They succeeded only after seeing an X-ray photograph of DNA that showed the double helix in detail. The image came from Rosalind Franklin’s unpublished data and was shared without her knowledge. Watson and Crick published their description in 1953, and with Maurice Wilkins they received the 1962 Nobel Prize in Physiology or Medicine. Franklin died in 1958, so she was not eligible for the prize.

How DNA Structure Was Discovered

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key terms and concepts

Explore how scientists uncovered DNA’s double helix, from Miescher’s nuclein to Chargaff’s rule, Franklin’s X-ray image, and Watson and Crick.

How DNA Structure Was Discovered | JoVE K12

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Inheritance and Variation of Traits

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How DNA Structure Was Discovered

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