BIOLOGY 283 Lecture 3: Problem Set 1

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Published on 16 Nov 2020
Department
BIO283 SEC 02 Spring 2020 Prof. Moscarella
Name: Michelle Shang SID: 31864094
Problem Set 1
1. In class, I presented a timeline highlighting important landmarks in the research to
determine the nature of the genetic material and the structure of DNA. One of those was
the work of Hershey and Chase. Briefly explain how did they contribute to the conclusion
that DNA was the genetic material? What technique helped them to distinguish between
viral DNA and protein? [4 pts]
Hershey and Chase used radioactive isotopes to trace the movement of DNA and protein during
phage infection of bacteria. This method helped them to distinguish viral DNA and protein
because DNA has phosphorus, not sulfur (using isotope 32P) and vice versa with protein. The
radioactive isotopes allowed for easy detection. They concluded that DNA is the genetic material
since the infected bacteria with the phosphorus isotope showed radioactivity in the progeny
phages and not the progeny phages in the bacteria infected by the sulfur isotope (used on
proteins).
2. Summarize the evidence found by Heinz Fraenkel-Conrat and Bea Singer that showed
that RNA serves as the genetic material in tobacco mosaic virus (TMV). [4 pts]
TMV contains a single molecule of RNA wrapped around by a helically arranged cylinder of
protein molecules. Fraenkel-Conrat separated the RNA and TMV protein and remixed them with
different strains of RNA and TMV protein. Using the mix, they created a hybrid virus to infect
tobacco leaves, where new viral particles were produced. They discovered that the new viral
progeny was identical to the isolated RNA strain and did not show characteristics of the donated
protein strain. From these results, they concluded that RNA carries the genetic information in
TMV.
3. A diploid human cell contains approximately 6.4 billion base pairs of DNA.
a.How many nucleosomes are present in such a cell? Show your work! (Hint: Each nucleosome
encompasses about 200 bp of DNA: 145147 bp of DNA wrapped around the histone core, 20
22 bp of DNA associated with the H1 protein, and another 3040 bp of linker DNA) [2 pts]
6.4 billion bp / 1 nucleosome (or 200 bp) = 32 million nucleosomes
b.Would you expect to find more molecules of the H1 histone or more molecules of the H2A
histone? [1 pt]
You would expect to find more molecules of the H2A histone because each nucleosome core
consists of two copies of the H2A histone and only 1 linker H1 histone.
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