3.04:_Ribosomes

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<p class="lt-bio-3968" style="background-color: unset;">Ribosomes are the protein-synthesizing machines of the cell. They <strong>translate</strong> the information encoded in <a title="3.4: Ribosomes" class="mt-self-link" href="/Sandboxes/johnnyphung/biology/03:_The_Cellular_Basis_of_Life/3.04:_Ribosomes"><strong>messenger RNA</strong></a> (<strong>mRNA</strong>) into a polypeptide.</p>

<span id="Shape.2C_size_and_function"></span><span id="Shape.2C_size_and_function"></span><h2 style="background-color: unset;" class="lt-bio-3968">Shape, size and function</h2>

<p class="lt-bio-3968" style="background-color: unset;">Ribosomes are roughly spherical with a diameter of ~20 nm, they can be seen only with the electron microscope. Figure <mjx-container class="MathJax CtxtMenu_Attached_0" jax="SVG" overflow="linebreak" tabindex="0" ctxtmenu_counter="96" style="font-size: 85%; position: relative;"><svg width="4.652ex" height="1.581ex" role="img" focusable="false" viewbox="0 -677 2056 699" aria-hidden="true" style="vertical-align: -0.05ex;"><defs><path id="MJX-97-NCM-N-33" d="M303 353C369 378 431 441 431 526C431 569 410 604 369 631C333 654 292 666 246 666C201 666 162 654 127 631C88 605 68 571 68 528C68 495 90 472 122 472C154 472 176 495 176 527C176 560 157 578 119 580C145 615 186 633 242 633C302 633 332 598 332 527C332 485 324 450 309 421C282 373 245 364 183 364C171 362 165 357 165 348C165 333 172 333 192 333L235 333C310 333 348 280 348 173C348 88 317 14 241 14C176 14 128 36 99 80C134 79 160 105 160 139C160 173 135 198 101 198C62 198 42 178 42 137C42 88 64 49 108 18C147-9 193-22 244-22C301-22 350-3 393 34C436 71 457 117 457 173C457 267 383 332 303 353Z"></path><path id="MJX-97-NCM-N-2E" d="M192 53C192 82 168 106 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data-semantic-role="sequence" data-semantic-annotation="depth:1" data-semantic-id="5" data-semantic-children="0,1,2,3,4" data-semantic-content="1,3" data-semantic-attributes="latex:\PageIndex{1};texclass:ORD" data-semantic-owns="0 1 2 3 4" data-semantic-level-number="0" data-speech-node="true"><g data-mml-node="mn" data-latex="3" data-semantic-type="number" data-semantic-role="integer" data-semantic-font="normal" data-semantic-annotation="clearspeak:simple;nemeth:number;depth:2" data-semantic-id="0" data-semantic-parent="5" data-semantic-attributes="latex:3" data-semantic-level-number="1" data-speech-node="true"><use data-c="33" href="#MJX-97-NCM-N-33"></use></g><g data-mml-node="TeXAtom" data-mjx-texclass="ORD" data-latex="{.}" transform="translate(500,0)"><g data-mml-node="mo" data-latex="." data-semantic-type="punctuation" data-semantic-role="fullstop" data-semantic-annotation="nemeth:number;depth:2" data-semantic-id="1" data-semantic-parent="5" 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data-semantic-level-number="1" data-speech-node="true"><use data-c="2E" href="#MJX-97-NCM-N-2E"></use></g></g><g data-mml-node="mn" data-latex="1" data-semantic-type="number" data-semantic-role="integer" data-semantic-font="normal" data-semantic-annotation="clearspeak:simple;nemeth:number;depth:2" data-semantic-id="4" data-semantic-parent="5" data-semantic-attributes="latex:1" data-semantic-level-number="1" data-speech-node="true" transform="translate(1556,0)"><use data-c="31" href="#MJX-97-NCM-N-31"></use></g></g></g></g></svg><mjx-assistive-mml unselectable="on" display="inline"><math data-latex="\PageIndex{1}" data-semantic-structure="(5 0 1 2 3 4)"><mrow data-mjx-texclass="ORD" data-latex="1}" data-semantic-type="punctuated" data-semantic-role="sequence" data-semantic-annotation="depth:1" data-semantic-="" data-semantic-children="0,1,2,3,4" data-semantic-content="1,3" data-semantic-attributes="latex:\PageIndex{1};texclass:ORD" data-semantic-owns="0 1 2 3 4" data-semantic-level-number="0" data-speech-node="true"><mn data-latex="3" data-semantic-type="number" data-semantic-role="integer" data-semantic-font="normal" data-semantic-annotation="clearspeak:simple;nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:3" data-semantic-level-number="1" data-speech-node="true">3</mn><mrow data-mjx-texclass="ORD" data-latex="{.}"><mo data-latex="." data-semantic-type="punctuation" data-semantic-role="fullstop" data-semantic-annotation="nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:{.};texclass:ORD" data-semantic-operator="punctuated" data-semantic-level-number="1" data-speech-node="true">.</mo></mrow><mn data-latex="4" data-semantic-type="number" data-semantic-role="integer" data-semantic-font="normal" data-semantic-annotation="clearspeak:simple;nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:4" data-semantic-level-number="1" data-speech-node="true">4</mn><mrow data-mjx-texclass="ORD" data-latex="{.}"><mo data-latex="." data-semantic-type="punctuation" data-semantic-role="fullstop" data-semantic-annotation="nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:{.};texclass:ORD" data-semantic-operator="punctuated" data-semantic-level-number="1" data-speech-node="true">.</mo></mrow><mn data-latex="1" data-semantic-type="number" data-semantic-role="integer" data-semantic-font="normal" data-semantic-annotation="clearspeak:simple;nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:1" data-semantic-level-number="1" data-speech-node="true">1</mn></mrow></math></mjx-assistive-mml></mjx-container> is an electron micrograph showing clusters of ribosomes. These clusters, called polysomes, are held together by messenger RNA (mRNA). They can make up 25% of the dry weight of cells (e.g., pancreas cells) and specialize in protein synthesis. A single pancreas cell can synthesize 5 million molecules of protein per minute.</p>

<figure><img class="internal" alt="Close-up view of a textured surface with clusters of small, rough, and rocky formations scattered across it. The surface appears black and white with varying shades of gray." loading="lazy" src="https://bio.libretexts.org/@api/deki/files/5373/ribosomes.jpg?revision=2" width="414" height="173" />
<figcaption>Figure <mjx-container class="MathJax CtxtMenu_Attached_0" jax="SVG" overflow="linebreak" tabindex="0" ctxtmenu_counter="97" style="font-size: 85%; position: relative;"><svg width="4.652ex" height="1.581ex" role="img" focusable="false" viewbox="0 -677 2056 699" aria-hidden="true" style="vertical-align: -0.05ex;"><defs><path id="MJX-98-NCM-N-33" d="M303 353C369 378 431 441 431 526C431 569 410 604 369 631C333 654 292 666 246 666C201 666 162 654 127 631C88 605 68 571 68 528C68 495 90 472 122 472C154 472 176 495 176 527C176 560 157 578 119 580C145 615 186 633 242 633C302 633 332 598 332 527C332 485 324 450 309 421C282 373 245 364 183 364C171 362 165 357 165 348C165 333 172 333 192 333L235 333C310 333 348 280 348 173C348 88 317 14 241 14C176 14 128 36 99 80C134 79 160 105 160 139C160 173 135 198 101 198C62 198 42 178 42 137C42 88 64 49 108 18C147-9 193-22 244-22C301-22 350-3 393 34C436 71 457 117 457 173C457 267 383 332 303 353Z"></path><path id="MJX-98-NCM-N-2E" d="M192 53C192 82 168 106 139 106C110 106 86 82 86 53C86 24 110 0 139 0C168 0 192 24 192 53Z"></path><path id="MJX-98-NCM-N-34" d="M353 677C344 677 336 672 330 663L28 199L28 163L289 163L289 81C289 63 285 51 278 46C271 41 252 39 219 39L194 39L194 0C223 2 269 3 331 3C393 3 439 2 468 0L468 39L443 39C410 39 391 41 384 46C377 51 373 63 373 81L373 163L471 163L471 202L373 202L373 660C373 670 366 677 353 677M295 553L295 202L67 202Z"></path><path id="MJX-98-NCM-N-31" d="M269 666C228 624 168 603 89 603L89 564C141 564 184 572 217 588L217 82C217 64 213 52 204 47C195 42 170 39 130 39L95 39L95 0C120 2 174 3 257 3C340 3 394 2 419 0L419 39L384 39C343 39 318 42 310 47C302 52 297 64 297 82L297 636C297 660 295 666 269 666Z"></path></defs><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math" data-latex="\PageIndex{1}" data-semantic-structure="(5 0 1 2 3 4)"><g data-mml-node="TeXAtom" data-mjx-texclass="ORD" data-latex="1}" data-semantic-type="punctuated" 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data-semantic-level-number="0" data-speech-node="true"><mn data-latex="3" data-semantic-type="number" data-semantic-role="integer" data-semantic-font="normal" data-semantic-annotation="clearspeak:simple;nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:3" data-semantic-level-number="1" data-speech-node="true">3</mn><mrow data-mjx-texclass="ORD" data-latex="{.}"><mo data-latex="." data-semantic-type="punctuation" data-semantic-role="fullstop" data-semantic-annotation="nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:{.};texclass:ORD" data-semantic-operator="punctuated" data-semantic-level-number="1" data-speech-node="true">.</mo></mrow><mn data-latex="4" data-semantic-type="number" data-semantic-role="integer" data-semantic-font="normal" data-semantic-annotation="clearspeak:simple;nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:4" data-semantic-level-number="1" data-speech-node="true">4</mn><mrow data-mjx-texclass="ORD" data-latex="{.}"><mo data-latex="." data-semantic-type="punctuation" data-semantic-role="fullstop" data-semantic-annotation="nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:{.};texclass:ORD" data-semantic-operator="punctuated" data-semantic-level-number="1" data-speech-node="true">.</mo></mrow><mn data-latex="1" data-semantic-type="number" data-semantic-role="integer" data-semantic-font="normal" data-semantic-annotation="clearspeak:simple;nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:1" data-semantic-level-number="1" data-speech-node="true">1</mn></mrow></math></mjx-assistive-mml></mjx-container>: An electron micrograph of polysomes held together with mRNA. Image courtesy of Alexander Rich.</figcaption>
</figure>

<p class="lt-bio-3968" style="background-color: unset;">In eukaryotes, ribosomes that synthesize proteins for use within the cytosol (e.g., enzymes of glycolysis) are suspended in the cytosol. The specific ribosomes that synthesize proteins destined for secretion (by exocytosis), the plasma membrane (e.g., cell surface receptors), and lysosomes. These ribosomes are attached to the cytosolic face of the membranes of the endoplasmic reticulum. As the polypeptide is synthesized, it is extruded into the interior (lumen) of the endoplasmic reticulum. Then, before these proteins reach their final destinations, they undergo a series of processing steps in the Golgi apparatus.</p>

<p class="lt-bio-3968" style="background-color: unset;">Ribosomes that synthesize 13 of the proteins destined for the inner membrane of mitochondria are found within the mitochondrion itself and are quite different in structure from the others. The ribosomes of bacteria, eukaryotes, and mitochondria differ in many details of their structure (Table <mjx-container class="MathJax CtxtMenu_Attached_0" jax="SVG" overflow="linebreak" tabindex="0" ctxtmenu_counter="98" style="font-size: 85%; position: relative;"><svg width="4.652ex" height="1.581ex" role="img" focusable="false" viewbox="0 -677 2056 699" aria-hidden="true" style="vertical-align: -0.05ex;"><defs><path id="MJX-99-NCM-N-33" d="M303 353C369 378 431 441 431 526C431 569 410 604 369 631C333 654 292 666 246 666C201 666 162 654 127 631C88 605 68 571 68 528C68 495 90 472 122 472C154 472 176 495 176 527C176 560 157 578 119 580C145 615 186 633 242 633C302 633 332 598 332 527C332 485 324 450 309 421C282 373 245 364 183 364C171 362 165 357 165 348C165 333 172 333 192 333L235 333C310 333 348 280 348 173C348 88 317 14 241 14C176 14 128 36 99 80C134 79 160 105 160 139C160 173 135 198 101 198C62 198 42 178 42 137C42 88 64 49 108 18C147-9 193-22 244-22C301-22 350-3 393 34C436 71 457 117 457 173C457 267 383 332 303 353Z"></path><path id="MJX-99-NCM-N-2E" d="M192 53C192 82 168 106 139 106C110 106 86 82 86 53C86 24 110 0 139 0C168 0 192 24 192 53Z"></path><path id="MJX-99-NCM-N-34" d="M353 677C344 677 336 672 330 663L28 199L28 163L289 163L289 81C289 63 285 51 278 46C271 41 252 39 219 39L194 39L194 0C223 2 269 3 331 3C393 3 439 2 468 0L468 39L443 39C410 39 391 41 384 46C377 51 373 63 373 81L373 163L471 163L471 202L373 202L373 660C373 670 366 677 353 677M295 553L295 202L67 202Z"></path><path id="MJX-99-NCM-N-31" d="M269 666C228 624 168 603 89 603L89 564C141 564 184 572 217 588L217 82C217 64 213 52 204 47C195 42 170 39 130 39L95 39L95 0C120 2 174 3 257 3C340 3 394 2 419 0L419 39L384 39C343 39 318 42 310 47C302 52 297 64 297 82L297 636C297 660 295 666 269 666Z"></path></defs><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math" data-latex="\PageIndex{1}" data-semantic-structure="(5 0 1 2 3 4)"><g 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data-semantic-attributes="latex:{.};texclass:ORD" data-semantic-operator="punctuated" data-semantic-level-number="1" data-speech-node="true"><use data-c="2E" href="#MJX-99-NCM-N-2E"></use></g></g><g data-mml-node="mn" data-latex="1" data-semantic-type="number" data-semantic-role="integer" data-semantic-font="normal" data-semantic-annotation="clearspeak:simple;nemeth:number;depth:2" data-semantic-id="4" data-semantic-parent="5" data-semantic-attributes="latex:1" data-semantic-level-number="1" data-speech-node="true" transform="translate(1556,0)"><use data-c="31" href="#MJX-99-NCM-N-31"></use></g></g></g></g></svg><mjx-assistive-mml unselectable="on" display="inline"><math data-latex="\PageIndex{1}" data-semantic-structure="(5 0 1 2 3 4)"><mrow data-mjx-texclass="ORD" data-latex="1}" data-semantic-type="punctuated" data-semantic-role="sequence" data-semantic-annotation="depth:1" data-semantic-="" data-semantic-children="0,1,2,3,4" data-semantic-content="1,3" data-semantic-attributes="latex:\PageIndex{1};texclass:ORD" data-semantic-owns="0 1 2 3 4" data-semantic-level-number="0" data-speech-node="true"><mn data-latex="3" data-semantic-type="number" data-semantic-role="integer" data-semantic-font="normal" data-semantic-annotation="clearspeak:simple;nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:3" data-semantic-level-number="1" data-speech-node="true">3</mn><mrow data-mjx-texclass="ORD" data-latex="{.}"><mo data-latex="." data-semantic-type="punctuation" data-semantic-role="fullstop" data-semantic-annotation="nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:{.};texclass:ORD" data-semantic-operator="punctuated" data-semantic-level-number="1" data-speech-node="true">.</mo></mrow><mn data-latex="4" data-semantic-type="number" data-semantic-role="integer" data-semantic-font="normal" data-semantic-annotation="clearspeak:simple;nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:4" data-semantic-level-number="1" data-speech-node="true">4</mn><mrow data-mjx-texclass="ORD" data-latex="{.}"><mo data-latex="." data-semantic-type="punctuation" data-semantic-role="fullstop" data-semantic-annotation="nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:{.};texclass:ORD" data-semantic-operator="punctuated" data-semantic-level-number="1" data-speech-node="true">.</mo></mrow><mn data-latex="1" data-semantic-type="number" data-semantic-role="integer" data-semantic-font="normal" data-semantic-annotation="clearspeak:simple;nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:1" data-semantic-level-number="1" data-speech-node="true">1</mn></mrow></math></mjx-assistive-mml></mjx-container>). However, despite these differences, the basic operations of bacterial, eukaryotic, and mitochondrial ribosomes are very similar.</p>

<table class="mt-responsive-table" align="center" border="1" cellpadding="1" cellspacing="2">
    <thead>
        <tr>
            <th align="center" colspan="1" scope="col"> </th>
            <th align="center" scope="col">Bacterial (70S)</th>
            <th align="center" scope="col">Eukaryotic (80S)</th>
            <th align="center" scope="col">Mitochondrial (55S)</th>
        </tr>
    </thead>
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data-semantic-level-number="0" data-speech-node="true"><mn data-latex="3" data-semantic-type="number" data-semantic-role="integer" data-semantic-font="normal" data-semantic-annotation="clearspeak:simple;nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:3" data-semantic-level-number="1" data-speech-node="true">3</mn><mrow data-mjx-texclass="ORD" data-latex="{.}"><mo data-latex="." data-semantic-type="punctuation" data-semantic-role="fullstop" data-semantic-annotation="nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:{.};texclass:ORD" data-semantic-operator="punctuated" data-semantic-level-number="1" data-speech-node="true">.</mo></mrow><mn data-latex="4" data-semantic-type="number" data-semantic-role="integer" data-semantic-font="normal" data-semantic-annotation="clearspeak:simple;nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:4" data-semantic-level-number="1" data-speech-node="true">4</mn><mrow data-mjx-texclass="ORD" data-latex="{.}"><mo data-latex="." data-semantic-type="punctuation" data-semantic-role="fullstop" data-semantic-annotation="nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:{.};texclass:ORD" data-semantic-operator="punctuated" data-semantic-level-number="1" data-speech-node="true">.</mo></mrow><mn data-latex="1" data-semantic-type="number" data-semantic-role="integer" data-semantic-font="normal" data-semantic-annotation="clearspeak:simple;nemeth:number;depth:2" data-semantic-="" data-semantic-parent="5" data-semantic-attributes="latex:1" data-semantic-level-number="1" data-speech-node="true">1</mn></mrow></math></mjx-assistive-mml></mjx-container>: Comparison of Ribosome Structure in Bacteria, Eukaryotes, and Human Mitochondria</caption>
    <tbody>
        <tr>
            <td align="center" class="lt-bio-3968" colspan="1" style="background-color: unset;"><strong>Large Subunit</strong></td>
            <td align="center" class="lt-bio-3968" data-th="Bacterial (70S)" style="background-color: unset;"><strong>50S</strong></td>
            <td align="center" class="lt-bio-3968" data-th="Eukaryotic (80S)" style="background-color: unset;"><strong>60S</strong></td>
            <td align="center" class="lt-bio-3968" data-th="Mitochondrial (55S)" style="background-color: unset;"><strong>39S</strong></td>
        </tr>
        <tr>
            <td align="center" class="lt-bio-3968" colspan="1" rowspan="3" style="background-color: unset;"><strong>rRNAs</strong><br />
            (1 of each)</td>
            <td class="mt-align-center lt-bio-3968" data-th="Bacterial (70S)" style="background-color: unset;">23S (2904 nts)</td>
            <td class="mt-align-center lt-bio-3968" data-th="Eukaryotic (80S)" style="background-color: unset;">28S (4700 nts)</td>
            <td align="center" class="lt-bio-3968" data-th="Mitochondrial (55S)" style="background-color: unset;">16S (1560 nts)</td>
        </tr>
        <tr>
            <td class="mt-align-center lt-bio-3968" data-th="Bacterial (70S)" style="background-color: unset;">5S (120 nts)</td>
            <td class="mt-align-center lt-bio-3968" data-th="Eukaryotic (80S)" style="background-color: unset;">5S (120 nts)</td>
            <td align="center" class="lt-bio-3968" data-th="Mitochondrial (55S)" rowspan="2" style="background-color: unset;">&nbsp;</td>
        </tr>
        <tr>
            <td align="center" class="lt-bio-3968" data-th="Bacterial (70S)" style="background-color: unset;">&nbsp;</td>
            <td align="center" class="lt-bio-3968" data-th="Eukaryotic (80S)" style="background-color: unset;">5.8S (160 nts)</td>
        </tr>
        <tr>
            <td align="center" class="lt-bio-3968" colspan="1" style="background-color: unset;"><strong>Proteins</strong></td>
            <td align="center" class="lt-bio-3968" data-th="Bacterial (70S)" style="background-color: unset;">35</td>
            <td align="center" class="lt-bio-3968" data-th="Eukaryotic (80S)" style="background-color: unset;">47</td>
            <td align="center" class="lt-bio-3968" data-th="Mitochondrial (55S)" style="background-color: unset;">50</td>
        </tr>
        <tr>
            <td align="center" class="lt-bio-3968" colspan="1" style="background-color: unset;"><strong>Small Subunit</strong></td>
            <td align="center" class="lt-bio-3968" data-th="Bacterial (70S)" style="background-color: unset;"><strong>30S</strong></td>
            <td align="center" class="lt-bio-3968" data-th="Eukaryotic (80S)" style="background-color: unset;"><strong>40S</strong></td>
            <td align="center" class="lt-bio-3968" data-th="Mitochondrial (55S)" style="background-color: unset;"><strong>28S</strong></td>
        </tr>
        <tr>
            <td align="center" class="lt-bio-3968" colspan="1" style="background-color: unset;"><strong>rRNA</strong></td>
            <td align="center" class="lt-bio-3968" data-th="Bacterial (70S)" style="background-color: unset;">16S (1542 nts)</td>
            <td align="center" class="lt-bio-3968" data-th="Eukaryotic (80S)" style="background-color: unset;">18S (1900 nts)</td>
            <td align="center" class="lt-bio-3968" data-th="Mitochondrial (55S)" style="background-color: unset;">12S (950 nts)</td>
        </tr>
        <tr>
            <td align="center" class="lt-bio-3968" colspan="1" style="background-color: unset;"><strong>Proteins</strong></td>
            <td align="center" class="lt-bio-3968" data-th="Bacterial (70S)" style="background-color: unset;">20</td>
            <td align="center" class="lt-bio-3968" data-th="Eukaryotic (80S)" style="background-color: unset;">33</td>
            <td align="center" class="lt-bio-3968" data-th="Mitochondrial (55S)" style="background-color: unset;">30</td>
        </tr>
        <tr>
            <td class="lt-bio-3968" colspan="4" data-th="Mitochondrial (55S)" style="background-color: unset;"><strong>S</strong> values are the sedimentation coefficient: a measure of the rate at which the particles are spun down in the ultracentrifuge. S values are not additive. nts = nucleotides.</td>
        </tr>
    </tbody>
</table>

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