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Unformatted text preview: t into mice, the mice did not get
pneumonia. When he injected heat-killed smooth and live rough, there was a transformation
and the mice got pneumonia (the heat-killed smooth transformed the rough into the virulent
smooth strain). Showed that some type of genetic material was surviving the heat-killing.
● Oswald Avery- Treated smooth virulent bacteria with protease (digests proteins), RNase
(digests RNA), and DNase (digests DNA). Mice stayed healthy only with the smooth bacteria
treated with DNase, so DNA is genetic material.
● Hershey-Chase- Used a virus that infects bacterial cells (bactereophage T2). Protein contains
sulfur and don’t contain phosphorus, DNA is opposite. They radioactively labeled the virus
and had it attack another cell to reproduce. The shell of the virus had sulfur, and the injected
material had phosphorus, so they knew the injected material was DNA.
What information did Watson and Crick have at their disposal that allowed them to
elucidate the structure of DNA?
● knew that DNA consists of monomers called nucleotides and that each nucleotide consists of
a nitrogenous base, a deoxyribose sugar, and a phosphate group.
● knew Chargaff's Rule- the amount of Guanine= the amount of Cytosine and the amount of
Adenine= the amount of Thymine (sticky letter, sticky letter, curvy letter, curvy letter)
● knew about Rosalind Franklin's X-ray diffraction which proved that DNA had a helical
What was it about Watson and Crick’s model of DNA that revealed how it stored
genetic information, and could pass that information from generation to generation?
The specific nucleotide base pairing in their model suggested a copying mechanism for genetic
Describe the experiment that showed that DNA replication was semi-conservative, as
the Watson and Crick model suggested?
Matthew Meselson and Franklin Stahl designed an experiment to determine the mechanism of DNA
replication. They reasoned that they could determine the method of replication by tracing the
origins of replicated DNA. Meselson and Stahl predicted the following:
● If the replication method were conservative, one round of replication would yield a DNA
molecule that contained two strands of parental DNA, and a second DNA molecule that
contained two new strands.
● If the replication method were semi-conservative, one round of replication would yield two
DNA molecules that each contained one strand of parental DNA and one strand of new DNA.
● If the replication method were dispersive, one round of replication would yield two DNA
molecules each containing mixtures of fragments of the original DNA as well as new
fragments of DNA.
They developed a way to tag the DNA strands using isotopes of nitrogen, 14N and 15N. By following the
tagged DNA through two rounds of replication, they were able to distinguish between the three
Meselson and Stahl's experiment confirmed that DNA replication follows the semi-conservative
model. According to the semiconservative model, each strand of the parent DNA molecule serves as
a template to produce a new complementary daughter strand. The resulting DNA molecule contains
one parent strand and one new daughter strand.
Describe the process of DNA r...
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