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Questions and Answers
What was the primary goal of the Hershey and Chase experiment in 1952?
What was the primary goal of the Hershey and Chase experiment in 1952?
- To identify the genetic material responsible for heredity (correct)
- To study the structure of bacteriophages
- To demonstrate the transformation of E. coli cells
- To prove that proteins are the blueprint of life
What was radiolabeled with radioactive sulfur-35 in the first experiment?
What was radiolabeled with radioactive sulfur-35 in the first experiment?
- The DNA inside the bacteriophage
- The E. coli cells
- The bacteriophage's outer membrane
- The protein capsid of the bacteriophage (correct)
What was the result of centrifugation in the first experiment?
What was the result of centrifugation in the first experiment?
- The E. coli cells formed a pellet at the bottom of the test tube (correct)
- The bacteriophage components formed a pellet at the top of the test tube
- The pellet contained the radioactive sulfur
- The supernatant contained the E. coli cells
What did the first experiment conclude about the protein capsid?
What did the first experiment conclude about the protein capsid?
What was radiolabeled with radioactive sulfur-32 in the second experiment?
What was radiolabeled with radioactive sulfur-32 in the second experiment?
What was the conclusion drawn from the experiment where radioactive phosphorus was used to infect bacteria?
What was the conclusion drawn from the experiment where radioactive phosphorus was used to infect bacteria?
What is the nature of the bond between sugar molecules in a DNA strand?
What is the nature of the bond between sugar molecules in a DNA strand?
Which of the following base pairs is characterized by triple hydrogen bonds?
Which of the following base pairs is characterized by triple hydrogen bonds?
What is the term for the ends of a DNA strand that are waiting for a phosphate group to attach?
What is the term for the ends of a DNA strand that are waiting for a phosphate group to attach?
What is the term for the areas of DNA that code for proteins?
What is the term for the areas of DNA that code for proteins?
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Study Notes
Hershey and Chase Experiment (1952)
- The Hershey and Chase experiment provided definitive proof that DNA is the blueprint of life
- The experiment consisted of two phases, using E. coli and bacteriophages (viruses that infect bacteria)
Phase 1: Radiolabeling the Protein Capsid
- Researchers radiolabeled the protein capsid of the bacteriophage with radioactive sulfur (Sulfur 35)
- They allowed the bacteriophage to infect E. coli, and then centrifuged the mixture
- The result: no radioactivity was present in the cells, indicating that the protein was not the transforming molecule (genetic material)
Phase 2: Radiolabeling the DNA
- Researchers radiolabeled the DNA inside the bacteriophage with radioactive phosphorus (Phosphorus 32)
- They allowed the bacteriophage to infect E. coli, and then centrifuged the mixture
- The result: the transformed bacteria were radioactive, indicating that DNA, not protein, was the transforming molecule (genetic material)
Basic Structure of DNA
Double Helix Structure
- DNA has a double helix structure, twisting because of the way the components connect to each other
- Each strand unwinds and zips open to reveal a single strand
Sugar and Phosphate Backbone
- The backbone of DNA consists of sugar (pentose) and phosphate groups
- Phosphate groups connect to the 5th carbon of the sugar
- Phosphodiester bonds connect sugars via the 3rd carbon
Nitrogenous Bases and Hydrogen Bonds
- The nitrogenous bases (Adenine, Thymine, Uracil, Guanine, and Cytosine) connect via hydrogen bonds
- Adenine only forms bonds with Thymine or Uracil (double bonds)
- Guanine only forms bonds with Cytosine (triple bonds)
- GC bonds are more difficult to unzip and open up than ATU bonds
- ATU regions often code for proteins
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