After allowing phages grown with bacteria in a medium that contained 32P and 35S, Hershey and Chase used a centrifuge to separat
e the phage ghosts from the infected cell. They then examined the infected cells and found that they contained _____, which demonstrated that _____ is the phage's genetic material. a) labeled DNA .... protein
b) labeled DNA ... labeled protein
c) labeled DNA ... DNA
d) labeled protein .... protein
e) labeled protein ... DNA
Hersey and Chase prepared two separate virus samples and infected the host cell, <em>E. coli</em>, that was present into different culture media. One of them contained a radioactive isotope of phosphorus (³²P) and the other contained a radioactive isotope of sulfur (³⁵S). After a division cycle in bacteria, all the viruses recently formed had one of the two isotopes depending on the culture media in which infected bacteria had grown. Viruses coming from bacteria incubated with ³²P had radioactive DNA whereas viruses coming from bacteria incubated with ³⁵S had radioactive proteins. This was due to the differences between the structures of the DNA and proteins: DNA contains phosphorus, but not sulfur and the proteins contain sulfur in cysteine and methionine, but not phosphorus.
After incubation, the cells were centrifugated to separate any extracellular viral material. Hersey and Chase found out that ³⁵S remained outside of the bacterial cells, in the empty capsids, and that ³²P had entered the cells and was present in the new viruses formed. They concluded that the genetic material was DNA and not the proteins.
DNA is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C). The order of these bases is what determines DNA's instructions, or genetic code.
