Video Experimental Relacionado
Updated: Aug 11, 2026
17:03
Direct Observation of Enzymes Replicating DNA Using a Single-molecule DNA Stretching Assay
Published on: March 24, 2010
El estiramiento excesivo del B-ADN: la respuesta elástica de las moléculas individuales de ADN de doble cadena y de
S B Smith1, Y Cui, C Bustamante
1Institute of Molecular Biology, University of Oregon, Eugene 97403, USA.
Science (New York, N.Y.)
|February 9, 1996
Resumen
El estiramiento del ADN de doble cadena (dsDNA) con pinzas láser reveló una forma estable y sobreestirada a 65 pN. Esta transición reversible, influenciada por la fuerza iónica, puede afectar la energía de recombinación del ADN.
Área de la Ciencia:
- Biología Molecular Biología Molecular
- La biofísica es la biofísica.
- La bioquímica es la bioquímica.
Sus antecedentes:
- Comprender la mecánica del ADN es crucial para la biología molecular.
- El ADN existe en varias formas estructurales más allá de la forma B canónica.
- Las propiedades mecánicas del ADN influyen en sus funciones biológicas.
Objetivo del estudio:
- Para investigar las propiedades mecánicas del ADN de doble cadena (dsDNA) bajo fuerza.
- Para caracterizar la transición a un estado de ADN sobreestirado.
- Para explorar los factores que afectan a esta transición del ADN.
Principales métodos:
- Utilizó pinzas láser de medición de fuerza para estirar moléculas de ADN individuales.
- Se aplicó una tensión longitudinal controlada al dsDNA en un tampón acuoso.
- Cambios medidos en la longitud del ADN y la reversibilidad de las transiciones estructurales.
Principales resultados:
- dsDNA sufre una transición cooperativa a una forma estable y sobreestirada a ~65 piconewtons (pN).
- Este ADN sobreestirado es un 70% más largo que el dsDNA de forma B, con un aumento de 5,8 angstroms por par de bases.
- La transición es reversible tras la relajación del estrés e influenciada por la fuerza iónica y la actividad del agua.
Conclusiones:
- La forma de ADN sobreestirado es un estado estable, inducido mecánicamente.
- Los factores ambientales como la fuerza iónica modulan las transiciones mecánicas del ADN.
- La conformación sobreestirada del ADN puede ser significativa en las energías de recombinación del ADN.
Videos de Conceptos Relacionados
01:02The DNA Replication Fork
An organism’s genome needs to be duplicated in an efficient and error-free manner for its growth and survival. The replication fork is a Y-shaped active region where two strands of DNA are separated and replicated continuously. The coupling of DNA unzipping and complementary strand synthesis is a characteristic feature of a replication fork. Organisms with small circular DNA, such as E. coli, often have a single origin of replication; therefore, they have only two replication forks, one in...
02:02DNA Topoisomerases
Topoisomerases are enzymes that relax overwound DNA molecules during various cell processes, including DNA replication and transcription. These enzymes regulate positive and negative DNA supercoiling without changing the nucleotide sequence. DNA overwinding in a clockwise direction results in positively supercoiled DNA, whereas underwinding in a counterclockwise direction produces negatively supercoiled DNA.
Types and Mechanism of action
Topoisomerases are divided into two main types. Type I...
Types and Mechanism of action
Topoisomerases are divided into two main types. Type I...
02:04Fixing Double-strand Breaks
The double-stranded structure of DNA has two major advantages. First, it serves as a safe repository of genetic information where one strand serves as the back-up in case the other strand is damaged. Second, the double-helical structure can be wrapped around proteins called histones to form nucleosomes, which can then be tightly wound to form chromosomes. This way, DNA chains up to 2 inches long can be contained within microscopic structures in a cell. A double-stranded break not only damages...
02:31Homologous Recombination
The basic reaction of homologous recombination (HR) involves two chromatids that contain DNA sequences sharing a significant stretch of identity. One of these sequences uses a strand from another as a template to synthesize DNA in an enzyme-catalyzed reaction. The final product is a novel amalgamation of the two substrates. To ensure an accurate recombination of sequences, HR is restricted to the S and G2 phases of the cell cycle. At these stages, the DNA has been replicated already and the...
01:03Single-Strand DNA Binding Proteins
For successful DNA replication, the unwinding of double-stranded DNA must be accompanied by stabilization and protection of the separated single strands of the DNA. This crucial task is performed by single-strand DNA-binding (SSB) proteins. They bind to the DNA in a sequence-independent manner, which means that the nitrogenous bases of the DNA need not be present in a specific order for binding of SSB proteins to it. The binding of SSB proteins straightens single-stranded DNA (ssDNA) and makes...
02:04Fixing Double-strand Breaks
The double-stranded structure of DNA has two major advantages. First, it serves as a safe repository of genetic information where one strand serves as the back-up in case the other strand is damaged. Second, the double-helical structure can be wrapped around proteins called histones to form nucleosomes, which can then be tightly wound to form chromosomes. This way, DNA chains up to 2 inches long can be contained within microscopic structures in a cell. A double-stranded break not only damages...