IB Biology HL Year 2: Hershey-Chase Experiment Review

Questions and Answers

In 1952, which two scientists showed that DNA (not protein) was the genetic material of cells?

Rosalind Franklin & Linus Pauling

Gregor Mendel & Charles Darwin

James Watson & Francis Crick

Alfred Hershey & Martha Chase (correct)

What did Alfred Hershey and Martha Chase show in their experiment?

DNA (not protein) was the genetic material of cells

How was evidence derived in the Hershey-Chase experiment?

Evidence was derived from studies that tracked viral infections of bacteria

____ consist of DNA (or RNA) enclosed by a protective coat of protein.

Viruses Signup and view all the answers

Viruses consist of _ (or _) enclosed by a protective coat of protein.

DNA (or RNA) Signup and view all the answers

What is a bacteriophage?

A category of viruses that infect bacteria cells Signup and view all the answers

In the Hershey-Chase experiment, T2 phage infected what bacteria cells?

E. coli Signup and view all the answers

Hershey-Chase designed an experiment where they were able to ______ the viral protein or DNA & then tracked which entered the E coli cell during infection.

Radiolabel Signup and view all the answers

Hershey-Chase designed an experiment where they were able to radiolabel the _ or _ & then tracked which entered the E coli cell during infection.

Viral protein or DNA Signup and view all the answers

What did radio labeling allow for in the Hershey-Chase experiment?

Allowed them to track the protein & track the DNA Signup and view all the answers

What was the hypothesis of Hershey and Chase for their experiment?

Whichever molecule (DNA or protein) enters into the bacteria must be responsible for allowing the virus to replicate & is thus the genetic material Signup and view all the answers

How did the virus replicate in the Hershey-Chase experiment?

The virus injects its genetic material into a host cell. The host cell then replicates the viral genetic material to make new viruses Signup and view all the answers

What elements make up DNA?

C, N, O, P, & no sulfur Signup and view all the answers

What elements make up protein?

C, N, O, S, & no phosphorus Signup and view all the answers

During the Hershey-Chase experiment, they grew one batch of T2 phage in the presence of radioactive _____, marking the proteins, but not the DNA.

Sulfur Signup and view all the answers

During the Hershey-Chase experiment, they grew a second batch of T2 phage in the presence of radioactive _____, marking the DNA, but not the proteins.

Phosphorus Signup and view all the answers

During the Hershey-Chase experiment, why was the blended mixture put into a centrifuge?

The centrifuge separated the heavier bacterial cells in the pellet from lighter free phages in a liquid supernatant Signup and view all the answers

What is a centrifuge?

Machine that spins & separates the contents inside based on density Signup and view all the answers

Define supernatant.

Liquid at the top of the tube Signup and view all the answers

In the Hershey-Chase experiment, was the viral coat found in the supernatant or the pellet?

Supernatant Signup and view all the answers

In the Hershey-Chase experiment, was the bacteria found in the supernatant or the pellet?

Pellet Signup and view all the answers

Define pellet.

Sediment at the bottom of the tube Signup and view all the answers

After the centrifuge, what were Hershey & Chase looking for in the pellet & the supernatant of the separate treatments?

The presence of radioactivity Signup and view all the answers

What was the result of the Hershey-Chase experiment?

They found that when the bacteria had been infected with T2 phages that contained radioactive DNA, the radioactivity was found in the bacterial pellet. Signup and view all the answers

Study Notes

Hershey-Chase Experiment Overview

Conducted in 1952 by Alfred Hershey and Martha Chase.
Determined that DNA, not protein, serves as the genetic material in cells.

Viruses

Composed of DNA or RNA encased in a protein coat.
Bacteriophages, or phages, specifically target bacterial cells.

Methodology

T2 phage was used to infect E. coli bacteria.
Experiment involved radiolabeling viral components (protein or DNA).

Radiolabeling Techniques

Proteins were marked with radioactive sulfur, avoiding labeling DNA.
DNA was marked with radioactive phosphorus, avoiding labeling proteins.
Allowed tracking of the respective viral material during infection.

Infection Process

Viruses inject their genetic material into the host.
The host cells then replicate the viral DNA to produce new viruses.

Experiment Steps

Infected cultures were subjected to blending to release any unabsorbed phage components.
Mixtures were then centrifuged to separate bacteria (pellet) from free phages (supernatant).

Centrifugation

Centrifuge spins mixtures, separating contents based on density.
Supernatant is the liquid portion, while the pellet consists of denser bacterial cells.

Results Analysis

Viral coats were found in the supernatant.
Bacteria remained in the pellet.
Radioactivity tests were conducted on both fractions to ascertain which viral components entered the bacteria.

Conclusions

Results confirmed that DNA, labeled with phosphorus, entered the bacterial cells.
Findings supported the hypothesis that DNA is the genetic material necessary for viral replication.

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Description

This quiz covers the discoveries made during the Hershey-Chase experiment, conducted by Alfred Hershey and Martha Chase in 1952. It reviews how this pivotal experiment demonstrated that DNA is the genetic material of cells, not proteins. Test your knowledge on the key concepts and findings associated with this significant scientific milestone.