Hershey and Chase: is it DNA or protein?
"Hershey and Chase: is it DNA or protein?" is a free, interactive Class 12 Biology simulation for NEET, built on the NCERT section "The search for genetic material" in Molecular Basis of Inheritance. Label phage protein with ³⁵S or DNA with ³²P, infect, blend, centrifuge, and see where radioactivity ends up. NEET has asked about this idea 2 times in 10 years of papers.
From the lesson The search for genetic material in Molecular Basis of Inheritance. Change the values and watch what happens.
What it shows
NCERT § The Search for Genetic Material
Label phage protein with ³⁵S or DNA with ³²P, infect, blend, centrifuge, and see where radioactivity ends up.
Controls
4 to try
- Togglelabel — ³⁵S / ³²P
- Buttoninfect → blend → centrifuge
- Toggleskip blending
- Readoutradioactivity in pellet (bacteria) vs supernatant
Try this
Run the version of the experiment whose pellet is radioactive and say what that labels.
Common mistake
Believing ³⁵S entered the bacteria.
In NEET
10 years of papers
Asked 2 times in 10 years of NEET.
See the past questions: DNA Double Helix, Molecular Basis of Inheritance (chapter)
The idea behind it
NCERT § "The Search for Genetic Material"
- Griffith (1928) used Streptococcus pneumoniae. The S strain has a smooth, shiny mucous (polysaccharide) coat and is virulent; the R strain has rough colonies, lacks the coat and is harmless to mice.
- Mice died from live S but not from live R or heat-killed S. Yet a mixture of live R with heat-killed S killed the mice, and live S bacteria were recovered from them.
- Griffith concluded that R bacteria had been transformed by some 'transforming principle' from the dead S cells, which let them make the coat and become virulent. He did not identify the chemical.
- Between 1933 and 1944, Oswald Avery, Colin MacLeod and Maclyn McCarty purified the biochemicals from heat-killed S cells. Transformation continued in the presence of proteases and RNases but was stopped by DNase, showing DNA to be the transforming substance. Not every biologist accepted this.
- Alfred Hershey and Martha Chase (1952) grew bacteriophages either with radioactive phosphorus, which labels DNA (proteins lack P), or with radioactive sulphur, which labels protein (DNA lacks S).
- The phages infected E. coli; blending then removed the viral coats and centrifugation separated the bacteria from the free virus particles.
- Bacteria infected by ³²P phages were radioactive, while those infected by ³⁵S phages were not, the ³⁵S staying in the supernatant. So DNA, not protein, enters the bacterium and is the genetic material.
Questions
4 answers
- What does the "Hershey and Chase: is it DNA or protein?" simulation show?
- Label phage protein with ³⁵S or DNA with ³²P, infect, blend, centrifuge, and see where radioactivity ends up.
- What mistake does the "Hershey and Chase: is it DNA or protein?" simulation fix?
- A common mistake it clears up: believing ³⁵S entered the bacteria.
- Has NEET asked about this idea?
- Yes. NEET has asked about this idea 2 times in 10 years of papers.
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "The search for genetic material" in Molecular Basis of Inheritance (Class 12 Biology).
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