Hershey and Chase Exp 2025

Entry Task

  • Copy/Drag the OneNote Tab: DNA and Protein Synthesis to your Name in the IB Bio OneNote Homework.

  • Pg. 2 Nucleic Acids Web Assignment.

  • Learning Target (LT): I can explain how Hershey & Chase identified DNA as the genetic material.

Agenda Today

  1. Pg 1: Hershey & Chase Experiment Notes.

  2. Nucleic Acids Web Assignment.

Hershey and Chase Experiment Overview

  • Confirmed DNA as hereditary material, not protein.

  • Participants: Alfred Hershey and Martha Chase (1953).

  • Significance in understanding genetic material.

Key Concepts

Building Blocks of Genetic Material

  • DNA comprises nucleic acids; there are four types of nucleic acids.

  • Proteins consist of 20 different amino acids.

  • Central question of the era: Do proteins or DNA carry genetic material?

Initial Assumptions

  • Proteins appeared to be better candidates for genetic diversity encoding due to:

    • Larger variety of building blocks (20 vs. 4).

    • Ability to store more complex information.

Experimental Design

Use of Bacteriophages

  • Bacteriophages: viruses that infect bacteria and replicate inside them.

  • Ideal model for testing genetic material due to:

    • Injection of genetic material into host cells.

    • Presence of both protein and DNA in the virus structure.

Experiment Methodology

  • Tagging techniques:

    • Virus protein coat labeled with radioactive sulfur.

    • Viral DNA labeled with radioactive phosphorus.

  • Objective: Determine if injected material was protein or DNA.

Observations and Findings

  • Post-experiment analysis yielded:

    • Presence of phosphorus in host cells after infection.

    • Absence of sulfur, indicating it was not injected into the bacteria.

    • Phosphorus must be linked to genetic material, reinforcing that DNA is the genetic material.

Experimental Details

Results of the Experiment

  • Bacteriophages had:

    • An external protein coat.

    • Internal DNA core.

  • Specified process:

    1. Infection of bacteria by bacteriophages.

    2. Blending of components to separate protein and DNA.

    3. Centrifugation to analyze components.

Conclusions Drawn

  • Findings indicated:

    • No sulfur detecting in cells (reinforces protein did not enter cells).

    • Detection of phosphorus in the cells supports the conclusion that nucleic acid is the genetic material, not protein.

Experimental Hypothesis

Hypotheses Overview

  • Hypothesis A: If protein is genetic material, then baby phages would have radioactive protein.

  • Hypothesis B: If nucleic acid is genetic material, then baby phages would have radioactive DNA.

Observations

  • Outcome: Observations led to the acceptance of Hypothesis B – nucleic acids being the genetic material.

  • Conclusion emphasized that despite proteins being perceived as more complex than DNA, the experiments strongly supported DNA as the genetic carrier.