Dna (English)
Páginas: 4 (812 palabras)
Publicado: 15 de octubre de 2012
How do we know that DNA is the genetic material?
The genetic material of an organism is the substance that contains the information specifying the inherited characteristics of that organism.When Mendel first postulated the existence of genes, he did not know the identity of the molecule that allows them to store and transmit inherited information. But a few years later, this molecule wasdiscovered by Miescher, a Swiss physician. The substance is now knows as DNA.
In his initial experiments, Miescher isolated nuclei from white blood cells obtained from pus found on surgicalbandages. Upon extracting these nuclei with alkali, he discovered an unusual substance, which is rich in phosphorus but unlike proteins contains no sulphur, which he called “nuclein”, which we now call DNA.Miescher rejected this idea after experimenting on fish, because his measuring incorrectly suggested that egg cells contain more DNA than sperm cells. Reasoning that the sperm and egg must contributeequal amounts of hereditary information to the offspring, it seemed to him that DNA could not be carrying hereditary information.
Around 1910 to the 1940’s, most scientists believed that genes weremade of protein rather than the DNA. Proteins seemed the logical choice at the time. Inherited traits exhibit extreme diversity so surely genes are very complex.
No single experiment, performed inany laboratory, led to the identification of DNA as the genetic material, until two lines of evidence resolved the matter in favour of DNA as the genetic material, as it’s described next.Griffith’s transformation experiment
Griffith was working with a bacterium that caused human pneumonia. He discovered that this bacterium exists in two forms called the S strain and the R strain. The IIIScauses disease and the IIR didn’t.
When injected into a mice, S-strain (not R-strain) bacteria trigger a fatal pneumonia. When it was injected with a mixture of live R-strain bacteria and dead...
The genetic material of an organism is the substance that contains the information specifying the inherited characteristics of that organism.When Mendel first postulated the existence of genes, he did not know the identity of the molecule that allows them to store and transmit inherited information. But a few years later, this molecule wasdiscovered by Miescher, a Swiss physician. The substance is now knows as DNA.
In his initial experiments, Miescher isolated nuclei from white blood cells obtained from pus found on surgicalbandages. Upon extracting these nuclei with alkali, he discovered an unusual substance, which is rich in phosphorus but unlike proteins contains no sulphur, which he called “nuclein”, which we now call DNA.Miescher rejected this idea after experimenting on fish, because his measuring incorrectly suggested that egg cells contain more DNA than sperm cells. Reasoning that the sperm and egg must contributeequal amounts of hereditary information to the offspring, it seemed to him that DNA could not be carrying hereditary information.
Around 1910 to the 1940’s, most scientists believed that genes weremade of protein rather than the DNA. Proteins seemed the logical choice at the time. Inherited traits exhibit extreme diversity so surely genes are very complex.
No single experiment, performed inany laboratory, led to the identification of DNA as the genetic material, until two lines of evidence resolved the matter in favour of DNA as the genetic material, as it’s described next.Griffith’s transformation experiment
Griffith was working with a bacterium that caused human pneumonia. He discovered that this bacterium exists in two forms called the S strain and the R strain. The IIIScauses disease and the IIR didn’t.
When injected into a mice, S-strain (not R-strain) bacteria trigger a fatal pneumonia. When it was injected with a mixture of live R-strain bacteria and dead...
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