3.17:_Chloroplasts

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<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-2"></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="Electron micrograph of a chloroplast with grana and stroma labeled." loading="lazy" src="https://bio.libretexts.org/@api/deki/files/6069/Shumway.jpg?revision=1" width="200" height="331" aria-describedby="remedy-description-7f5c252146b512c8" /><span id="remedy-description-7f5c252146b512c8" data-remedy-image-description="7f5c252146b512c8" style="display: block; white-space: pre-line;">An elongated chloroplast occupies most of the image. Green pointer lines labeled Grana identify dense stacks of internal membranes. An orange line labeled Stroma points to the lighter material between the stacks. A boundary encloses the organelle; no scale bar is visible.</span>
<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>

<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 (creativecommons.org)</a>  license and was authored, remixed, and/or curated by <a rel="nofollow" target="_blank" href="http://www.biology-pages.info/">John W. Kimball (biology-pages.info)</a> via <a rel="nofollow" href="https://www.biology-pages.info/" target="_blank">source content (biology-pages.info)</a> that was edited to the style and standards of the LibreTexts platform.</p></div>

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