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12 Cards in this Set
- Front
- Back
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What was the purpose of the first experiment? |
This convinced scientists that DNA did carry out the genetic code. |
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What did they use for this experiment? |
Bacteriophages. |
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What are bacteriophages? |
A virus
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What do bacteriophages do? |
They bind to the surface of bacteria and pass DNA into the cell. The protein remains outside the cell. The viral DNA then uses amino acids, nucleotides and ribosomes in the cell to make new viruses. The new viruses then break out of the cell and destroy it.
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What did scientists do in the experiment? |
They made viruses with DNA that contained a radioactive isotope of phosphorous and proteins with a radioactive isotope of sulphur in them. The viruses were allowed to infect bacteria and then the bacteria were tested to see whether or not they had taken up DNA or protein. |
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What did they observe and what did this tell them? |
The radioactive sulphur was only found outside the cell, whereas the phosphorous was found inside the cell. This indicates that it's the viral DNA which carries the genetic code and not the proteins which remained outside of the cell. |
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Why didn't they use a radioactive isotope of carbon? |
Both proteins and DNA contain carbon so they'd be indistinguishable. Sulphur is used in proteins as they sometime contain sulphur. Phosphorous was used because DNA contains phosphorous. |
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What was the purpose of experiment 2?
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It was to decipher the RNA code |
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How was this done? |
A cytoplasm extract was treated with DNAase to remove any existing DNA which may have made its own mRNA. They then added all 20 amino acids attached to tRNA but labelled phenylalanine with a radioactive isotope of carbon. They then placed synthetic mRNA of 3 types into the mixture. |
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What were the results? |
The sequences of just A and just C showed minimal background radiation. The mRNA sequence with just U showed the most radiation in the polypeptide. |
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What did this do? |
This allowed them to figure out which amino acids were produced by the different mRNA codons.
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Why isn;t it possible to decipher all codons this way? |
Some have a mixture of bases |
