Before Alfred Hershey and Martha Chase convinced the worldthat DNA actually stor
ID: 5085 • Letter: B
Question
Before Alfred Hershey and Martha Chase convinced the worldthat DNA actually stores genetic information, the macromoleculethat was suspected of being the potential source of geneticinformation was ________________. To differentiate between DNA and this macromolecule, Hersheyand Chase produced phages with radioactive ____________ in theirDNA and radioactive ___________ in thier ________. Watson and Crick proposed that in DNA _______ is always pairedwith _______(use the letters), and __________ is always paired with________(use the letters). This pairing scheme was based on___________ rules (name researcher who described it). WILL RATE lifesaver if all are correct-much Thanks! Before Alfred Hershey and Martha Chase convinced the worldthat DNA actually stores genetic information, the macromoleculethat was suspected of being the potential source of geneticinformation was ________________. To differentiate between DNA and this macromolecule, Hersheyand Chase produced phages with radioactive ____________ in theirDNA and radioactive ___________ in thier ________. Watson and Crick proposed that in DNA _______ is always pairedwith _______(use the letters), and __________ is always paired with________(use the letters). This pairing scheme was based on___________ rules (name researcher who described it). WILL RATE lifesaver if all are correct-much Thanks!Explanation / Answer
answer
protein
radioactive sulfur or radioactive phosphorus.
chargraff rule
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The experiment that Hershey and Chase devised to differentiatebetween these possibilities was simple and took advantage of thedifferences in the composition of protein and DNA.Protein contains sulfur, DNA doesn't. Protein contains a smallamount of phosphorus; DNA contains a lot of phosphorus.
Hershey and Chase added bacteriophage to cultures containingeither radioactive sulfur or radioactive phosphorus. Thebacteriophages grown in the cultures with radioactive sulfur pickedit up and incorporated it into their protein. The bacterial virusesgrown in the culture with radioactive phosphorus picked that up,incorporating a little of it into the protein, but most of it intotheir DNA. Hershey and Chase now had two types of bacteriophages:one with a radioactive external protein coat, the other with highlyradioactive DNA. They were ready to begin their experiment.
Each of the two types of radioactive bacteriophage was added toa separate culture of bacteria. The bacteriophages were allowed toinfect the bacteria, then the cultures were whirled in a kitchenblender, causing any part of the bacteriophages that hadn't gotinside the bacteria to fall off. Next the cultures were spun in acentrifuge, which separates materials suspended in liquid accordingto their weights. The heavier bacterial cells fell to the bottomand formed a pellet, the lighter bacteriophages and loose phageparts remained in the liquid.
Where was the radioactivity now? It depended on whichradioactive element you looked for. In the cultures infected bybacteriophages with radioactive sulfur (with labeled protein), mostof the radioactivity was in the liquid with the phages. In thecultures infected by bacteriophages with radioactive phosphorus(with most of the label in their DNA), most of the radioactivitywas in the pellet of infected bacteria. Thus, the radioactiveprotein hadn't entered the bacterial cells, but the DNA had.
The final proof that DNA, not protein, was the genetic materialwas provided by the offspring of the phosphorus-labeledbacteriophages. They had radioactive DNA, passed down from theirparents, but no radioactive protein. These experiments convincedthe scientific community that DNA alone was the material ofheredity, and inspired Watson and Crick to begin their efforts todiscover its structure.
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