Study Of Martha Chase And Hershey Experiment
Hershey and Chase Experiment
In 1953, Alfred Hershey and Martha Chase confirmed DNA's preeminent role in genetics by demonstrating that DNA is the genetic material of a virus called phage T2.
The phage, which infects E. coli, consists of a head, sheath, tail, and base plate made of different proteins. DNA is packaged within the head of the virus.
When T2 comes in contact with E. coli, the phage attaches to the bacterium by its tail. Next, the phage injects genetic material into the cell. The genetic material directs bacterial enzymes to produce viral offspring.
When the life cycle is complete, 100 to 200 progeny phages have been assembled inside each bacterium. The bacterium breaks open, or lyses, and the phages are released
Since T2 consists …show more content…
coli cell into a T2-producing factory that releases phages when the cell ruptures.
To determine the source of genetic material in the phage, Hershey and Chase designed an experiment in which they could label protein or DNA and then track which entered the E. coli cell during infection.
They grew one batch of T2 phage in the presence of radioactive sulfur, marking the proteins but not DNA.
They grew another batch in the presence of radioactive phosphorus, marking the DNA but not proteins.
They allowed each batch to infect separate E. coli cultures.
Shortly after the onset of infection, they spun the cultured infected cells in a blender, shaking loose any parts of the phage that remained outside the bacteria.
The mixtures were spun in a centrifuge, which separated the heavier bacterial cells in the pellet from lighter free phages and parts of phage in the liquid supernatant.
They then tested the pellet and supernatant of the separate treatments for the presence of radioactivity.
Hershey and Chase found that when the bacteria had been infected with T2 phages that contained radiolabeled proteins, most of the radioactivity was in the supernatant that contained phage particles, not in the pellet with the …show more content…
CHAGRAFF https://www.youtube.com/watch?v=HvJlnujmYcg By 1947, Erwin Chargaff had developed a series of rules based on a survey of DNA composition in organisms.
He already knew that DNA was a polymer of nucleotides consisting of a nitrogenous base, deoxyribose, and a phosphate group.
The bases could be adenine (A), thymine (T), guanine (G), or cytosine (C).
Chargaff noted that the DNA composition varies from species to species.
In any one species, the four bases are found in characteristic, but not necessarily equal, ratios.
He also found a peculiar regularity in the ratios of nucleotide bases that are known as Chargaff’s rules.
In all organisms, the number of adenines was approximately equal to the number of thymines (%T = %A).
The number of guanines was approximately equal to the number of cytosines (%G = %C).
Human DNA is 30.9% adenine, 29.4% thymine, 19.9% guanine, and 19.8% cytosine.
The basis for these rules remained unexplained until the discovery of the double
In 1953, Alfred Hershey and Martha Chase confirmed DNA's preeminent role in genetics by demonstrating that DNA is the genetic material of a virus called phage T2.
The phage, which infects E. coli, consists of a head, sheath, tail, and base plate made of different proteins. DNA is packaged within the head of the virus.
When T2 comes in contact with E. coli, the phage attaches to the bacterium by its tail. Next, the phage injects genetic material into the cell. The genetic material directs bacterial enzymes to produce viral offspring.
When the life cycle is complete, 100 to 200 progeny phages have been assembled inside each bacterium. The bacterium breaks open, or lyses, and the phages are released
Since T2 consists …show more content…
coli cell into a T2-producing factory that releases phages when the cell ruptures.
To determine the source of genetic material in the phage, Hershey and Chase designed an experiment in which they could label protein or DNA and then track which entered the E. coli cell during infection.
They grew one batch of T2 phage in the presence of radioactive sulfur, marking the proteins but not DNA.
They grew another batch in the presence of radioactive phosphorus, marking the DNA but not proteins.
They allowed each batch to infect separate E. coli cultures.
Shortly after the onset of infection, they spun the cultured infected cells in a blender, shaking loose any parts of the phage that remained outside the bacteria.
The mixtures were spun in a centrifuge, which separated the heavier bacterial cells in the pellet from lighter free phages and parts of phage in the liquid supernatant.
They then tested the pellet and supernatant of the separate treatments for the presence of radioactivity.
Hershey and Chase found that when the bacteria had been infected with T2 phages that contained radiolabeled proteins, most of the radioactivity was in the supernatant that contained phage particles, not in the pellet with the …show more content…
CHAGRAFF https://www.youtube.com/watch?v=HvJlnujmYcg By 1947, Erwin Chargaff had developed a series of rules based on a survey of DNA composition in organisms.
He already knew that DNA was a polymer of nucleotides consisting of a nitrogenous base, deoxyribose, and a phosphate group.
The bases could be adenine (A), thymine (T), guanine (G), or cytosine (C).
Chargaff noted that the DNA composition varies from species to species.
In any one species, the four bases are found in characteristic, but not necessarily equal, ratios.
He also found a peculiar regularity in the ratios of nucleotide bases that are known as Chargaff’s rules.
In all organisms, the number of adenines was approximately equal to the number of thymines (%T = %A).
The number of guanines was approximately equal to the number of cytosines (%G = %C).
Human DNA is 30.9% adenine, 29.4% thymine, 19.9% guanine, and 19.8% cytosine.
The basis for these rules remained unexplained until the discovery of the double