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

L'acido desossiribonucleico, o DNA, è costituito da due catene polinucleotidiche.
Ognuna di queste catene è composta da quattro tipi di subunità nucleotidiche.
Ogni nucleotide è costituito da un singolo gruppo fosfato e da una base contenente azoto: adenina, A, citosina, C, guanina, G o timina, T, attaccata a uno zucchero desossiribosio.
Questa disposizione crea la spina dorsale zucchero-fosfato della struttura del DNA.
Lungo la spina dorsale di ogni filamento, i legami fosfodiestere legano covalentemente il terzo atomo di carbonio di uno zucchero al quinto atomo di carbonio della successiva molecola di zucchero nella catena.
Nei filamenti antiparalleli opposti, ogni base è accoppiata in modo univoco, C con G e A con T, a causa delle differenze nel numero di legami idrogeno che si formano tra di loro.
Tale polarità chimica garantisce un impacchettamento efficiente, avvolgendo i due filamenti l'uno attorno all'altro per formare una doppia elica 3D, con dieci coppie di basi ogni giro completo.

l'elica del dna

L’acido desossiribonucleico, o DNA, è il materiale genetico responsabile della trasmissione dei tratti di generazione in generazione in tutti gli organismi e nella maggior parte dei virus. Il DNA è composto da due filamenti di nucleotidi che si avvolgono l'uno attorno all'altro per formare una struttura a molla chiamata doppia elica. Tuttavia, la doppia elica non è perfettamente simmetrica. Invece, ci sono scanalature regolari nella struttura. Il solco principale si verifica dove le strutture portanti zucchero-fosfato sono relativamente distanti. Questo spazio garantisce l'accesso alle proteine che legano il DNA, come i fattori di trascrizione. Il solco minore, al contrario, si verifica dove le strutture portanti zucchero-fosfato sono vicine tra loro. Relativamente poche proteine si legano al DNA attraverso il solco minore.

La scoperta della struttura del DNA: una breve storia

La scoperta della struttura del DNA è avvenuta in modo incrementale nel corso di quasi un secolo, rappresentando una delle storie più famose e avvincenti della storia della scienza.

Tutto ebbe inizio nel 1869 quando lo scienziato svizzero Friedrich Miescher scoprì una sostanza che chiamò "nucleina". Durante il processo di estrazione delle proteine dai globuli bianchi, Miescher trovò una sostanza inaspettata che aveva un contenuto di fosforo relativamente elevato. Non sapeva cosa fosse, ma sospettava che potesse essere biologicamente importante. Miescher aveva ragione, ma ci sono voluti decenni perché la comunità scientifica apprezzasse appieno le sue intuizioni.

La successiva scoperta fondamentale fu fatta dal biochimico russo Phoebus Levene. Nel 1919, Levene propose che la nucleina, allora nota come acido nucleico, fosse composta da catene di molecole che chiamò polinucleotidi. La proposta di Levene derivava dalla sua ricerca sul lievito, in cui scoprì che i singoli nucleotidi erano composti da un gruppo fosfato, uno zucchero e una base contenente azoto. Sebbene il modello polinucleotidico di Levene fosse corretto sotto molti aspetti, non era ancora chiaro come fossero disposte le basi nella molecola del DNA.

Il biochimico austriaco Erwin Chargaff ha ampliato il lavoro di Levene. Lavorando alla fine degli anni Quaranta, Chargaff fece una scoperta fondamentale: la quantità di adenina nel DNA è sempre più o meno uguale alla quantità di timina, e la quantità di guanina è sempre più o meno uguale a quella di citosina. Questo modello divenne noto come Regola di Chargaff e fu una prova chiave che permise la delucidazione finale della struttura del DNA.

All'inizio degli anni '50, il biologo americano James Watson e il fisico inglese Francis Crick stavano gareggiando con il loro principale rivale, l'americano Linus Pauling, per scoprire la struttura tridimensionale del DNA. Basandosi sul lavoro di Chargaff, usarono la conoscenza della fisica, della matematica e della chimica per costruire modelli fisici del DNA. Ma non hanno avuto successo finché non hanno ricevuto un dato fondamentale: una “fotografia” a raggi X del DNA che indicava in dettaglio preciso la sua struttura a doppia elica. Questa fotografia costituiva i dati inediti del fisico Rosalind Franklin e fu data a Watson e Crick all'insaputa di Franklin. Watson e Crick pubblicarono la loro descrizione della struttura del DNA nel 1953 e, insieme a Maurice Wilkins (un collaboratore di Franklin), vinsero nel 1962 il Premio Nobel per la Fisiologia e la Medicina per questa scoperta. Purtroppo, Franklin morì nel 1958 e non poté ricevere il Premio Nobel.

L'elica del DNA

L'acido desossiribonucleico, o DNA, è il materiale genetico responsabile della trasmissione dei tratti di generazione in generazione in tutti gli organismi e nella maggior parte dei virus. DNA...

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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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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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How DNA Structure Was Discovered

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