Name: the genetic code and codons
Uploaded: 2020-09-24T15:06:53.000Z
Duration: 3 min 6 s
Channel: JoVE

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High School

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From Molecules To Organisms: Structures And Processes

HS-LS1-1

From DNA to Protein

El ADN contiene genes, secuencias de nucleótidos, algunos de los cuales son instrucciones que codifican la serie de aminoácidos de una proteína. El flujo de información genética del ADN al ARN y a la proteína es un proceso conocido como El Dogma Central. El primer paso de este proceso es la transcripción, donde una enzima ARN polimerasa sintetiza una copia o transcripción del gen basada en ARN.El ADN se utiliza como plantilla donde cada nueva base de ARN agregada a la transcripción es complementaria a la hebra original de ADN. Algunas transcripciones, llamadas mensajero o ARNm, codifican proteínas, mientras que las no codificantes participan en otros procesos celulares. Por ejemplo, el ARNr ribosómico y el ARNt de transferencia participan en la síntesis de proteínas.El siguiente paso es la traducción, donde se decodifica el ARNm para sintetizar una cadena de aminoácidos. Para leer el ARNm, se utiliza un conjunto de instrucciones conocidas como código genético para leer el ARNm. La mayoría de los organismos usan este mismo código universal compuesto por tres grupos de nucleótidos llamados codones que se traducen en aminoácidos específicos.Hay 64 tripletes de nucleótidos diferentes, pero solo 20 aminoácidos estándar en las proteínas hacen que el código se degenere, es decir, múltiples conjuntos de codones pueden dar la misma instrucción. Sesenta y uno establecen el código para los aminoácidos y tres señalan el final de la traducción. La traducción se produce en el ribosoma, un gran complejo de ARNr y proteínas, con la ayuda del ARNt.El ARNt tiene una estructura de tres bucles en horquilla. Un bucle contiene una secuencia denominada anticodón, que tiene bases complementarias al codón. Un aminoácido correspondiente a esta secuencia se une al final del ARNt, que lo transporta al ribosoma.Las proteínas llamadas factores de iniciación unen la unidad de ribosoma pequeña, un ARNt iniciador y el ARNm. Después del ensamblaje del complejo, el ribosoma se desliza a lo largo del ARNm en busca del sitio de inicio de la traducción. Aquí, el anticodón del ARNt iniciador se une al codón complementario;la unidad de ribosoma grande se une al ensamblaje y se inicia la traducción.Cuando llega el siguiente ARNt, el aminoácido del iniciador se separa y se transfiere al aminoácido vecino, lo que da como resultado una cadena polipeptídica en crecimiento. La adición de aminoácidos continúa hasta que se detecta un codón de parada en el ARNm. Luego, el ribosoma libera la cadena para que pueda plegarse en una proteína funcional.

del adn a la proteína

El flujo de información genética en las células del ADN al ARNm a la proteína se describe por el dogma central, que establece que los genes especifican la secuencia de los ARNm, que a su vez especifican la secuencia de los aminoácidos que componen todas las proteínas. La decodificación de una molécula a otra se realiza mediante proteínas y ARN específicos. Debido a que la información almacenada en el ADN es tan importante para la función celular, tiene sentido intuitivo que la célula haría copias de ARNm de esta información para la síntesis de proteínas, manteniendo el ADN mismo intacto y protegido. La copia de ADN a ARN es relativamente sencilla, con un nucleótido que se añade a la cadena de ARNm para cada nucleótido leído en la cadena de ADN. La traducción a proteína es un poco más compleja porque tres nucleótidos de ARNm corresponden a un aminoácido en la secuencia de polipéptidos. Sin embargo, la traducción proteica es todavía sistemática y colineal, tal que los nucleótidos 1 a 3 corresponden al aminoácido 1, los nucleótidos 4 a 6 corresponden al aminoácido 2, y así sucesivamente.
 El Código genético es degenerado y universal
 Cada aminoácido se define por una secuencia de tres nucleótidos llamada codón o triplete. Dados los diferentes números de “letras” en los “alfabetos” del ARNm y las proteínas, los científicos teorizaron que los aminoácidos individuales deben estar representados por combinaciones de nucleótidos. Los dobletes de nucleótidos no serían suficientes para especificar cada aminoácido porque sólo hay 16 combinaciones posibles de dos nucleótidos (42). En contraste, hay 64 posibles tripletes de nucleótidos (43), que es mucho más que el número de aminoácidos. Los científicos teorizaron que los aminoácidos estaban codificados por tripletes de nucleótidos y que el código genético era “degenerado”. En otras palabras, un aminoácido dado podría ser codificado por más de un triplete de nucleótido. Esto fue confirmado experimentalmente más tarde: Francis Crick y Sydney Brenner usaron el químico mutágeno proflavina para insertar uno, dos o tres nucleótidos en el gen de un virus. Cuando se insertaron uno o dos nucleótidos, no se produjeron las proteínas normales. Cuando se insertaron tres nucleótidos, la proteína fue sintetizada y funcional. Esto demostró que los aminoácidos deben ser especificados por grupos de tres nucleótidos. Estos tripletes de nucleótidos se llaman codones. La inserción de uno o dos nucleótidos cambió completamente el marco de lectura del triplete, alterando así el mensaje para cada aminoácido subsiguiente. Aunque la inserción de tres nucleótidos hizo que se insertara un aminoácido adicional durante la traducción, se mantuvo la integridad del resto de la proteína.
 Además de los codones que instruyen la adición de un aminoácido específico a una cadena de polipéptidos, tres de los 64 codones terminan la síntesis de proteínas y liberan el polipéptido de la maquinaria de traducción. Estos tripletes se llaman codones sin sentido o codones de parada. Otro codón, AUG, también tiene una función especial. Además de especificar el aminoácido metionina, también sirve como codón de inicio para iniciar la traducción. El marco de lectura para la traducción es establecido por el codón de inicio AUG cerca del extremo de 5′ del ARNm. Después del codón de inicio, el ARNm se lee en grupos de tres nucleótidos hasta que se encuentra un codón de parada.
 La especificación de un solo aminoácido por múltiples codones similares se llama "degeneración". Se cree que la degeneración es un mecanismo celular para reducir el impacto negativo de las mutaciones aleatorias. Los codones que especifican el mismo aminoácido normalmente sólo difieren por un nucleótido. Además, los aminoácidos con cadenas laterales químicamente similares están codificados por codones similares. Por ejemplo, el aspartato (Asp) y el glutamato (Glu), que ocupan el bloque GA*, están cargados negativamente. Este matiz del código genético asegura que una mutación de sustitución de un solo nucleótido podría especificar el mismo aminoácido pero no tener ningún efecto o especificar un aminoácido similar, evitando que la proteína se haga completamente no funcional.
 El código genético es casi universal. Con pocas excepciones menores, prácticamente todas las especies utilizan el mismo código genético para la síntesis de proteínas. La conservación de codones significa que un ARNm purificado que codifica la proteína globina en caballos podría ser transferido a una célula de tulipán, y el tulipán sintetizaría la globina de caballo. Que sólo haya un código genético es una poderosa evidencia de que toda la vida en la Tierra comparte un origen común, especialmente considerando que hay cerca de 1084 combinaciones posibles de 20 aminoácidos y 64 codones.
 Este texto ha sido adaptado de<a href="https://openstax.org/books/biology-2e/pages/15-1-the-genetic-code"> Openstax, Biología 2e, Capítulo 15.1:</a><a href="https://openstax.org/books/biology-2e/pages/15-1-the-genetic-code"> El Código Genético</a>.

Del ADN a la Proteína

El flujo de información genética en las células desde el ADN hasta el ARNm y la proteína se describe mediante el dogma central, que establece que los genes especifican la secuencia de ...

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KEY TERMS AND CONCEPTS

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the genetic code and codons

The genetic code and codons explain how cells turn DNA information into proteins. Genes first direct the sequence of mRNA, and mRNA then directs the sequence of amino acids that make up proteins. Specific proteins and RNAs carry out this decoding. Cells copy DNA into mRNA so the original DNA stays protected while the cell uses the message for protein synthesis.

Copying DNA to RNA is relatively simple. One nucleotide is added to the mRNA strand for every nucleotide read on the DNA strand. Translating mRNA into protein is more complex because three mRNA nucleotides correspond to one amino acid. Even so, the process is orderly and stays collinear. Nucleotides 1 to 3 specify amino acid 1, nucleotides 4 to 6 specify amino acid 2, and the pattern continues in the same way.

Each amino acid is defined by a three-nucleotide codon, also called a triplet codon. Scientists proposed this idea because the mRNA and protein alphabets are different sizes. Two-nucleotide combinations would not be enough, since there are only 16 possible doublets. Three-nucleotide combinations provide 64 possible triplets, which is far more than the number of amino acids. This led to the idea that the code is degenerate, meaning one amino acid can be encoded by more than one codon.

Francis Crick and Sydney Brenner tested this idea with the chemical mutagen proflavin. They inserted one, two, or three nucleotides into a virus gene. Inserting one or two nucleotides prevented normal proteins from being made. Inserting three nucleotides still allowed a functional protein to be synthesized. This showed that amino acids are read in groups of three. One- or two-nucleotide insertions shift the reading frame and change every later amino acid, while a three-nucleotide insertion adds one amino acid but preserves the rest of the protein.

Some codons do not add amino acids. Three of the 64 codons are stop codons, also called nonsense codons, and they end protein synthesis. Another codon, AUG, has two roles. It codes for methionine and also acts as the start codon that begins translation. The AUG start codon near the 5' end of the mRNA sets the reading frame. After that, the mRNA is read in groups of three until a stop codon appears.

Degeneracy may help reduce the effects of random mutations. Codons that specify the same amino acid usually differ by only one nucleotide. Amino acids with similar side chains are also often encoded by similar codons. For example, aspartate and glutamate are both negatively charged and fall in the GA* codon block. This means a single-nucleotide substitution may have no effect, or it may lead to a similar amino acid instead of a harmful change.

The genetic code is nearly universal. With a few minor exceptions, most species use the same code to make proteins. This shared code means a purified mRNA for horse globin could be placed in a tulip cell, and the tulip would make horse globin. The near-universal code is also strong evidence that life on Earth shares a common origin, especially since there are about 10^84 possible combinations of 20 amino acids and 64 triplet codons.

The Genetic Code and Codons

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The genetic code and codons explain how cells turn DNA information into proteins. Genes first direct the sequence of mRNA, and mRNA then directs the sequence of amino acids that make up proteins. Specific proteins and RNAs carry out this decoding. Cells copy DNA into mRNA so the original DNA stays protected while the cell uses the message for protein synthesis. Copying DNA to RNA is relatively simple. One nucleotide is added to the mRNA strand for every nucleotide read on the DNA strand.

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Learn how codons, stop signals, and the AUG start codon guide protein synthesis, and why the genetic code is nearly universal across species.

The Genetic Code and Codons | JoVE K12

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JoVE Core Química da vida a los conceptos de química general mediante lecciones de vídeo basadas en animaciones, concisas y fáciles de entender. Además, en los vídeos de científicos en acción, se muestran experimentos de investigación clásicos y originales realizados en laboratorios de todo el mundo.

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New York State Science Learning Standards

Life Science

Structure and Function

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Matter and Energy in Organisms and Ecosystems

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DNA Packaging

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RNA Structure

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HS-LS1-2

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HS-LS1-3

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HS-LS1-4

The Genetic Code and Codons

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