3.08:_Lysosomes_and_Peroxisomes

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<p class="lt-bio-3972" style="background-color: unset;">A cell is composed of many different organelles and microbodies (or cytosomes) is a type of organelle that is found in the cells of plants, protozoa, and animals. Organelles in the microbody family include peroxisomes, glyoxysomes, glycosomes and hydrogenosomes.</p>

<span id="Lysosomes"></span><h2 style="background-color: unset;" class="lt-bio-3972">Lysosomes</h2>

<p class="lt-bio-3972" style="background-color: unset;">Lysosomes are roughly spherical bodies enclosed by a single membrane. They are manufactured by the Golgi apparatus (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="1.557ex" role="img" focusable="false" viewbox="0 -666 2056 688" 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 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and contain over 50 different kinds of hydrolytic enzymes including proteases, lipases, nucleases, and polysaccharidases. The pH within the lysosome is about pH 5, substantially less than that of the cytosol (~pH 7.2). All the enzymes in the lysosome work best at an acid pH, which reduces the risk of their digesting their own cell if they should escape from the lysosome.</p>

<figure><img alt="1024px-Endocytic_pathway_of_animal_cells_showing_EGF_receptors,_transferrin_receptors_and_mannose-6-phosphate_receptors.jpg" style="width: 739px; height: 647px;" width="739px" height="647px" class="internal" loading="lazy" src="https://bio.libretexts.org/@api/deki/files/12460/1024px-Endocytic_pathway_of_animal_cells_showing_EGF_receptors%252C_transferrin_receptors_and_mannose-6-phosphate_receptors.jpg?revision=1&amp;size=bestfit&amp;width=739&amp;height=647" /><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="1.557ex" role="img" focusable="false" viewbox="0 -666 2056 688" 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-38" d="M250 666C201 666 158 650 122 618C86 586 68 546 68 497C68 456 83 419 113 386C120 378 142 361 179 335C88 288 42 227 42 153C42 100 64 57 107 24C147-7 194-22 249-22C305-22 354-4 395 32C436 68 457 115 457 170C457 216 441 257 408 294C396 307 365 330 316 361C393 402 431 454 431 515C431 606 344 666 250 666M379 515C379 463 348 418 286 381L167 459C136 479 120 505 120 536C120 596 185 633 249 633C318 633 379 584 379 515M250 14C168 14 99 73 99 153C99 220 136 274 210 315L328 240C376 209 400 174 400 134C400 62 325 14 250 14Z"></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" 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 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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-98-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="8" 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:8" data-semantic-level-number="1" data-speech-node="true">8</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><em><strong>:</strong> Lysosome manufacturing process The lysosome is shown in purple, as an endpoint in Endocytotic sorting. AP2 is necessary for vesicle formation, whereas the Mannose-6-receptor is necessary for sorting Hydrolase into the Lysosome's lumen. Image used wtih permission (CC BY-SA; Matthew R G Russell).</em></figcaption></figure>

<p class="lt-bio-3972" style="background-color: unset;">Materials within the cell scheduled for digestion are first deposited within lysosomes. These may be:</p>

<ul>
    <li class="lt-bio-3972" style="background-color: unset;">other organelles, such as mitochondria, that have ceased functioning properly and have been engulfed in <strong>autophagosomes</strong></li>
    <li class="lt-bio-3972" style="background-color: unset;">food molecules or, in some cases, food particles taken into the cell by endocytosis</li>
    <li class="lt-bio-3972" style="background-color: unset;">foreign particles like bacteria that are engulfed by neutrophils</li>
    <li class="lt-bio-3972" style="background-color: unset;">antigens that are taken up by</li>
    <li class="lt-bio-3972" style="background-color: unset;">&quot;professional&quot; antigen-presenting cells like dendritic cells (by phagocytosis) and</li>
    <li class="lt-bio-3972" style="background-color: unset;">B cells (by binding to their antigen receptors (BCRs) followed by receptor-mediated endocytosis.</li>
</ul>

<div class="box-note">
<p class="lt-bio-3972" style="background-color: unset;">At one time, it was thought that lysosomes were responsible for killing cells scheduled to be removed from a tissue; for example, the resorption of its tail as the tadpole metamorphoses into a frog. This is incorrect. These examples of programmed cell death (PCD) or apoptosis take place by an entirely different mechanism.</p>
</div>

<p class="lt-bio-3972" style="background-color: unset;">In some cells, lysosomes have a secretory function &mdash; releasing their contents by exocytosis.</p>

<ul>
    <li class="lt-bio-3972" style="background-color: unset;">Cytotoxic T cells (CTL) secrete perforin from lysosomes.</li>
    <li class="lt-bio-3972" style="background-color: unset;">Mast cells secrete some of their many mediators of inflammation from modified lysosomes.</li>
    <li class="lt-bio-3972" style="background-color: unset;">Melanocytes secrete melanin from modified lysosomes.</li>
    <li class="lt-bio-3972" style="background-color: unset;">The exocytosis of lysosomes provides the additional membrane needed to quickly <strong>seal wounds</strong> in the plasma membrane.</li>
</ul>

<div class="box-note"><span id="Lysosomal_Storage_Diseases"></span><h5 class="box-legend"><span class="lt-icon-default">Lysosomal Storage Diseases</span></h5>

<p class="lt-bio-3972" style="background-color: unset;">Lysosomal storage diseases are caused by the accumulation of macromolecules (proteins, polysaccharides, lipids) in the lysosomes because of a genetic failure to manufacture an enzyme needed for their breakdown. Neurons of the central nervous system are particularly susceptible to damage. Most of these diseases are caused by the inheritance of two defective alleles of the gene encoding <strong>one</strong> of the hydrolytic enzymes. Examples include:</p>

<ul>
    <li class="lt-bio-3972" style="background-color: unset;"><strong>Tay-Sachs disease</strong> and <strong>Gaucher's disease</strong> &mdash; both caused by a failure to produce an enzyme needed to break down sphingolipids (fatty acid derivatives found in all cell membranes).</li>
    <li class="lt-bio-3972" style="background-color: unset;"><strong>Mucopolysaccharidosis I</strong> (MPS-I). Caused by a failure to synthesize an enzyme (&alpha;-<small><font size="2">L</font></small>-iduronidase) needed to break down proteoglycans like heparan sulfate. In April 2003, the U.S. Food and Drug Administration approved a synthetic version of the enzyme, laronidase (Aldurazyme&reg;), as a possible treatment. This enzyme (containing 628 amino acids) is manufactured by recombinant DNA technology.</li>
</ul>

<p class="lt-bio-3972" style="background-color: unset;">However, one lysosomal storage disease, <strong>I-cell disease</strong> (&quot;inclusion-cell disease&quot;), is caused by a failure to &quot;tag&quot; (by phosphorylation) <strong>all</strong> the hydrolytic enzymes that are supposed to be transported from the Golgi apparatus to the lysosomes. Lacking the mannose 6-phosphate (M6P) tag, they are secreted from the cell instead. The result: all the macromolecules incorporated in lysosomes remain undegraded forming &quot;inclusion bodies&quot; in the cell.</p>
</div>

<span id="Peroxisomes"></span><h2 style="background-color: unset;" class="lt-bio-3972">Peroxisomes</h2>

<p class="lt-bio-3972" style="background-color: unset;">Peroxisomes, also called microbodies, are about the size of lysosomes (0.5&ndash;1.5 &micro;m) and like them are enclosed by a single membrane. They also resemble lysosomes in being filled with enzymes. However, peroxisomes bud off from the endoplasmic reticulum, not the Golgi apparatus (the source of lysosomes) and the enzymes and other proteins destined for peroxisomes are synthesized in the cytosol. Each contains a <strong>p</strong>eroxisomal <strong>t</strong>argeting <strong>s</strong>ignal (<strong>PTS</strong>) that binds to a receptor molecule that takes the protein into the peroxisome and then returns for another load. Two peroxisomal targeting signals have been identified: a 9-amino acid sequence at the N-terminal of the protein and a tripeptide at the C-terminal. Each has its own receptor to take it to the peroxisome.</p>

<p class="lt-bio-3972" style="background-color: unset;">Functions of the peroxisomes in the human liver inlcude:</p>

<ul>
    <li class="lt-bio-3972" style="background-color: unset;">Breakdown (by oxidation) of excess fatty acids.</li>
    <li class="lt-bio-3972" style="background-color: unset;">Breakdown of hydrogen peroxide (H<sub><font size="2">2</font></sub>O<sub><font size="2">2</font></sub>), a potentially dangerous product of fatty-acid oxidation. It is catalyzed by the enzyme catalase.</li>
    <li class="lt-bio-3972" style="background-color: unset;">Participates in the synthesis of cholesterol. One of the enzymes involved, HMG-CoA reductase, is the target of the popular cholesterol-lowering &quot;statins&quot;.</li>
    <li class="lt-bio-3972" style="background-color: unset;">Participates in the synthesis of bile acids.</li>
    <li class="lt-bio-3972" style="background-color: unset;">Participates in the synthesis of the lipids used to make myelin.</li>
    <li class="lt-bio-3972" style="background-color: unset;">Breakdown of excess purines (AMP, GMP) to uric acid.</li>
</ul>

<p class="lt-bio-3972" style="background-color: unset;">Peroxisomes are also present in plant cells where they participate is such functions as symbiotic nitrogen fixation and photorespiration.</p>

<div class="box-note"><span id="Peroxisome_Disorders"></span><h5 class="box-legend"><span class="lt-icon-default">Peroxisome Disorders</span></h5>

<p class="lt-bio-3972" style="background-color: unset;">A variety of rare inherited disorders of peroxisome function occur in humans. Most involve mutant versions of one or another of the enzymes found within peroxisomes. For example: <strong>X-linked adrenoleukodystrophy</strong> (<strong>X-ALD</strong>) results from a failure to metabolize fatty acids properly. One result is deterioration of the myelin sheaths of neurons. The disorder occurs in young boys because the gene is X-linked. An attempt to find an effective treatment was the subject of the 1992 film <strong>Lorenzo's Oil</strong>. A few diseases result from failure to produce functional peroxisomes. For example: <strong>Zellweger syndrome</strong> results from the inheritance of two mutant genes for one of the receptors (PXR1) needed to import proteins into the peroxisome.</p>
</div>

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<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/3.08:_Lysosomes_and_Peroxisomes">3.8: Lysosomes and Peroxisomes</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>

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