3.17:_Chloroplasts

view live ↗

<p class="lt-bio-3995" style="background-color: unset;">A typical plant cell (e.g., in the palisade layer of a leaf) might contain as many as 50 chloroplasts.</p>

<figure><img class="internal" alt="Diagram of a chloroplast showing an outer membrane, intermembrane space, inner membrane, stroma, granum, thylakoid membrane, and thylakoid lumen." loading="lazy" src="https://bio.libretexts.org/@api/deki/files/6081/chloroplast1.gif?revision=1" /><figcaption>Figure 3.17.1 Typical Chloroplast</figcaption></figure>

<p class="lt-bio-3995" style="background-color: unset;">The chloroplast is made up of 3 types of membrane:</p>

<ul>
    <li class="lt-bio-3995" style="background-color: unset;">A smooth <strong>outer membrane</strong> which is freely permeable to molecules.</li>
    <li class="lt-bio-3995" style="background-color: unset;">A smooth <strong>inner membrane</strong> which contains many <strong>transporters</strong>: integral membrane proteins that regulate the passage in an out of the chloroplast of
    <ul>
        <li class="lt-bio-3995" style="background-color: unset;">small molecules like sugars</li>
        <li class="lt-bio-3995" style="background-color: unset;">proteins synthesized in the cytoplasm of the cell but used within the chloroplast</li>
    </ul>
    </li>
    <li class="lt-bio-3995" style="background-color: unset;">A system of <strong>thylakoid membranes</strong></li>
</ul>

<span id="Thylakoids"></span><span id="Thylakoids"></span><h2 style="background-color: unset;" class="lt-bio-3995">Thylakoids</h2>

<p class="lt-bio-3995" style="background-color: unset;">The thylakoid membranes enclose a lumen: a system of vesicles (that may all be interconnected). At various places within the chloroplast these are stacked in arrays called <strong>grana</strong> (resembling a stack of coins). Four types of protein assemblies are embedded in the thylakoid membranes: These carry out the so-called light reactions of photosynthesis including:</p>

<ol>
    <li class="lt-bio-3995" style="background-color: unset;"><strong>Photosystem I</strong> which includes chlorophyll and carotenoid molecules</li>
    <li class="lt-bio-3995" style="background-color: unset;"><strong>Photosystem II</strong> which also contains chlorophyll and carotenoid molecules</li>
    <li class="lt-bio-3995" style="background-color: unset;"><strong>Cytochromes b</strong> and <strong>f</strong></li>
    <li class="lt-bio-3995" style="background-color: unset;"><strong>ATP synthase</strong></li>
</ol>

<p class="lt-bio-3995" style="background-color: unset;">The thylakoid membranes are surrounded by a fluid <strong>stroma,</strong> which contains all the enzymes, e.g., RUBISCO, needed to carry out the &quot;dark&quot; reactions of photosynthesis; that is, the conversion of CO<sub><font size="2">2</font></sub> into organic molecules like glucose. A number of identical molecules of DNA, each of which carries the complete chloroplast genome. The genes encode some &mdash; but not all of the molecules needed for chloroplast function. The others are</p>

<ul>
    <li class="lt-bio-3995" style="background-color: unset;">transcribed from genes in the <strong>nucleus</strong> of the cell</li>
    <li class="lt-bio-3995" style="background-color: unset;">translated in the cytoplasm and</li>
    <li class="lt-bio-3995" style="background-color: unset;">transported into the chloroplast.</li>
</ul>

<figure><img class="internal" alt="Black and white electron microscope image of a bacterial cell labeled with green text Mesosomes, Bacterial Cytoplasm, and red text Bacterial Structure." loading="lazy" src="https://bio.libretexts.org/@api/deki/files/6069/Shumway.jpg?revision=1" width="200" height="331" />
<figcaption>Figure 3.17.2 Chloroplast from a corn cell courtesy of Dr. L. K. Shumway</figcaption>
</figure>

<figure><img class="internal" alt="Close-up of textured, gray surface with a grid-like pattern and irregular white patches, resembling snow or frost." loading="lazy" src="https://bio.libretexts.org/@api/deki/files/6073/Miller_K.jpg?revision=1" />
<figcaption>Figure 3.17.3 Inner surface of thylakoid courtesy of Kenneth R. Miller</figcaption>
</figure>

<p class="lt-bio-3995" style="background-color: unset;">The electron micrograph in Figure 3.17.3 shows the inner surface of a thylakoid membrane. Each particle may represent one photosystem II complex. In the functioning chloroplast, these particles may not be as highly ordered as seen here.</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/03:_The_Cellular_Basis_of_Life/3.17:_Chloroplasts">3.17: Chloroplasts</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