5.02:_The_Hershey_-_Chase_Experiments

view live ↗

<p class="lt-bio-4740" style="background-color: unset;">In 1952 (seven years after Avery's demonstration that genes were DNA), two geneticists: A. D. Hershey and Martha Chase, provided further proof. They worked with a DNA virus, called <strong>T2</strong>, which infects <em>E. coli</em> (and so is a bacteriophage). Figure 5.2.1 shows the essential elements of the infective cycle of DNA bacteriophages like T2. The virions attach to the surface of their host cell <strong>(a)</strong>. The proteins of the capsid inject the <strong>DNA core</strong> into the cell <strong>(b)</strong>. Once within the cell, some of the bacteriophage genes (the &quot;early&quot; genes) are transcribed (by the host's RNA polymerase) and translated (by the host's ribosomes, tRNA, etc.) to produce enzymes that will make many copies of the phage DNA and will turn off (even destroy) the host's DNA.</p>

<figure><img class="internal" alt="Diagram showing the process of bacteriophage replication: attachment, penetration, biosynthesis, maturation, and release, with viruses infecting and emerging from bacterial cells." loading="lazy" src="https://bio.libretexts.org/@api/deki/files/6521/T4.gif?revision=1" /><figcaption>Figure 5.2.1: The Hershey - Chase Experiment</figcaption></figure>

<p class="lt-bio-4740" style="background-color: unset;">As fresh copies of phage DNA accumulate, other genes (the &quot;late&quot; genes) are transcribed and translated to form the proteins of the capsid <strong>(c)</strong>. The stockpile of DNA cores and capsid proteins are assembled into complete virions <strong>(d)</strong>. Another &quot;late&quot; gene is transcribed and translated into molecules of lysozyme. The lysozyme attacks the peptidoglycan wall (from the inside, of course). Eventually the cell ruptures and releases its content of virions ready to spread the infection to new host cells <strong>(e)</strong>.</p>

<p class="lt-bio-4740" style="background-color: unset;">Bacteriophages produced within bacteria growing in radioactive culture medium will themselves be radioactive. If radioactive sulfur atoms (<sup><small><font size="1">35</font></small></sup>S) are present, they will be incorporated into the protein coats of the bacteriophages since two of the amino acids &mdash; cysteine and methionine &mdash; contain sulfur (Figure 5.2.2). However, the DNA will be nonradioactive because there are no sulfur atoms in DNA. If radioactive phosphorus (<sup><small><font size="1">32</font></small></sup>P) is used instead, the DNA become radioactive &mdash; because of its many phosphorus atoms &mdash; but not the proteins.</p>

<figure><img height="408" width="516" class="internal" alt="Diagram showing the Hershey-Chase experiment with bacteriophages. Red labels protein; green indicates DNA. Steps include infection, blending, and centrifugation, highlighting genetic material transfer." loading="lazy" src="https://bio.libretexts.org/@api/deki/files/6517/Hershey_Chase_experiment.png?revision=1" /><figcaption>Figure 5.2.2: Diagram of the Hershey Chase experiment.  (GFDL; Thomasione )</figcaption></figure>

<p class="lt-bio-4740" style="background-color: unset;">Hershey and Chase found that when bacteriophages containing <sup><small><font size="1">32</font></small></sup>P (radioactive), were allowed to infect nonradioactive bacteria, all the infected cells became radioactive and, in fact, much of the radioactivity was passed on to the next generation of bacteriophages. However, when the bacteria were infected with bacteriophages labeled with <sup><small><font size="1">35</font></small></sup>S, and then the virus coats removed (by whirling them in an electric blender), practically no radioactivity could be detected in the infected cells. From these experiments, it was clear that the DNA component of the bacteriophages is injected into the bacterial cell while the protein component remains outside. However, it is the injected component &mdash; DNA &mdash; that is able to direct the formation of new virus particles <strong>complete</strong> with protein coats. So here is further proof that <strong>genes are DNA</strong>.</p>

function loadMathJaxScript() {
    try {
    	const script = document.createElement('script');
      script.id = "mathjax-script";
    	script.src = "https://cdn.jsdelivr.net/npm/mathjax@4/tex-mml-svg.js";
    	script.type = "text/javascript";
      script.defer = true;

document.head.appendChild(script);
    } catch (err) {
        console.error(err);
    }
}

document.addEventListener('DOMContentLoaded', (e) => {
	loadMathJaxScript();
});

if (window.PageName !== 'Realtime MathJax'){
MathJax = {
  options: {
    ignoreHtmlClass: "tex2jax_ignore",
    processHtmlClass: "tex2jax_process",
    menuOptions: {
      settings: {
        zscale: "150%",
        zoom: "Double-Click",

assistiveMml: true, // true to enable assitive MathML
        collapsible: false, // true to enable collapsible math
      },
    },
  },
  output: {
    scale: 0.85,
    mtextInheritFont: false,
    displayOverflow: "linebreak",
    linebreaks: {
      width: "100%",
    },
  },
  startup: {
    pageReady: () => {
      if (window.activateBeeLine) {
        window.activateBeeLine();
      }
      return MathJax.startup.defaultPageReady();
    },
  },
  chtml: {
    matchFontHeight: true,
  },
  tex: {
    tags: "all",
    tagformat: {
      number: (n) => {
        if (window.InitialOffset) {
          const offset = Number(window.InitialOffset);
         	if(!offset) {
          	return front + n; // If offset is falsy (nan, undefined, etc.)
          }
          const added = Number(n) + offset;
          return front + added;
        } else {
          return front + n;
       	}
      },
    },
    macros: {
      eatSpaces: ['#1', 2, ['', ' ', '\\endSpaces']],
      PageIndex: ['{' + front.replace(/\./g, '{.}') + '\\eatSpaces#1 \\endSpaces}', 1],
      test: ["{" + front + "#1}", 1],
      mhchemrightleftharpoons: "{\\unicode{x21CC}\\,}",
      xrightleftharpoons: ['\\mhchemxrightleftharpoons[#1]{#2}', 2, '']
    },
    packages: {
      "[+]": [
        "mhchem",
        "color",
        "cancel",
        "ams",
        "tagformat"
      ],
    },
  },
  loader: {
    '[tex]/mhchem': {
      ready() {
        const {MapHandler} = MathJax._.input.tex.MapHandler;
        const mhchem = MapHandler.getMap('mhchem-chars');
        mhchem.lookup('mhchemrightarrow')._char = '\uE42D';
        mhchem.lookup('mhchemleftarrow')._char = '\uE42C';
      }
    },
    load: [
      "[tex]/mhchem",
      "[tex]/color",
      "[tex]/cancel",
      "[tex]/tagformat",
    ],
  },
};
};
///*]]>*/</script>

<hr class="autoattribution-divider" /><div class="autoattribution"><p>This page titled <a target="_blank" class="internal mt-self-link" href="/Sandboxes/johnnyphung/biology/05:_DNA/5.02:_The_Hershey_-_Chase_Experiments">5.2: The Hershey - Chase Experiments</a> is shared under a <a rel="nofollow" href="https://creativecommons.org/licenses/by/3.0" target="_blank">CC BY  3.0</a>  license and was authored, remixed, and/or curated by <a rel="nofollow" target="_blank" href="http://www.biology-pages.info/">John W. Kimball</a> via <a rel="nofollow" href="https://www.biology-pages.info/" target="_blank">source content</a> that was edited to the style and standards of the LibreTexts platform.</p></div>

Reset