4.11:_Metabolism

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<p class="lt-bio-4648" style="background-color: unset;">All living things must have an unceasing supply of energy and matter. The transformation of this energy and matter within the body is called <strong>metabolism</strong>.</p>

<span id="Catabolism_and_Anabolism"></span><span id="Catabolism_and_Anabolism"></span><h2 style="background-color: unset;" class="lt-bio-4648">Catabolism and Anabolism</h2>

<p class="lt-bio-4648" style="background-color: unset;">Catabolism is <strong>destructive metabolism</strong>. Typically, in catabolism, larger organic molecules are broken down into smaller constituents. This usually occurs with the release of energy (usually as ATP). Anabolism is <strong>constructive metabolism</strong>. Typically, in anabolism, small precursor molecules are assembled into larger organic molecules. This always requires the input of energy (often as ATP).</p>

<span id="Autotrophic_vs._Heterotrophic_Nutrition"></span><span id="Autotrophic_vs._Heterotrophic_Nutrition"></span><h2 style="background-color: unset;" class="lt-bio-4648">Autotrophic vs. Heterotrophic Nutrition</h2>

<p class="lt-bio-4648" style="background-color: unset;">Green plants, algae, and some bacteria are <strong>autotrophs</strong> (&quot;self-feeders&quot;). Most of them use the energy of sunlight to assemble inorganic precursors, chiefly carbon dioxide and water, into the array of organic macromolecules of which they are made. The process is <strong>photosynthesis</strong>. Photosynthesis makes the ATP needed for the anabolic reactions in the cell. All other organisms, including ourselves, are <strong>heterotrophs</strong>. We secure all our energy from organic molecules taken in from our surroundings (&quot;food&quot;). Although heterotrophs may feed partially (as most of us do) or exclusively on other heterotrophs, all the food molecules come ultimately from autotrophs. We may eat beef but the steer ate grass. Heterotrophs degrade some of the organic molecules they take in (catabolism) to make the ATP that they need to synthesize the others into the macromolecules of which they are made (anabolism).</p>

<span id="How_humans_(and_other_animals)_do_it"></span><span id="How_humans_(and_other_animals)_do_it"></span><h2 style="background-color: unset;" class="lt-bio-4648">How humans (and other animals) do it</h2>

<p class="lt-bio-4648" style="background-color: unset;">Humans are heterotrophs. We are totally dependent on ingested preformed organic molecules to meet all our <strong>energy</strong> needs. We are also dependent on preformed organic molecules as the building blocks to meet our <strong>anabolic</strong> needs.</p>

<figure><img class="internal" alt="Diagram showing human excretory system. Labeled: lungs, liver, sweat glands, kidneys, skin, alimentary canal, with arrows indicating metabolic waste removal routes." loading="lazy" src="https://bio.libretexts.org/@api/deki/files/6328/topology.gif?revision=1" /><figcaption>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="5.783ex" height="1.532ex" role="img" focusable="false" viewbox="0 -677 2556 677" aria-hidden="true" style="vertical-align: 0px;"><defs><path id="MJX-97-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-97-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 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data-semantic-attributes="latex:1" data-semantic-level-number="1" data-speech-node="true" transform="translate(2056,0)"><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="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="11" 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:11" data-semantic-level-number="1" data-speech-node="true">11</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>: Human Topology</figcaption></figure>

<p class="lt-bio-4648" style="background-color: unset;">The steps for converting food to energy in animals:</p>

<ol>
    <li class="lt-bio-4648" style="background-color: unset;"><strong>Ingestion</strong>: taking food within the body (although as the figure shows, it is still topologically in the external world, not the internal).</li>
    <li class="lt-bio-4648" style="background-color: unset;"><strong>Digestion: </strong>The enzyme-catalyzed hydrolysis of polysaccharides (e.g., starch) to sugars, proteins to amino acids, fats to fatty acids and glycerol, and nucleic acids to nucleotides.</li>
    <li class="lt-bio-4648" style="background-color: unset;"><strong>Absorption</strong> into the body and transport to the cells.</li>
    <li class="lt-bio-4648" style="background-color: unset;"><strong>Absorption </strong>into cells.</li>
</ol>

<figure><img class="internal" alt="A flowchart illustrating a decision-making process, including actions like Assess situation, Develop alternatives, and Implement alternative. Arrows connect each step with additional decisions." loading="lazy" src="https://bio.libretexts.org/@api/deki/files/6329/MetabolicPathways.gif?revision=1" /><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="5.783ex" height="1.532ex" role="img" focusable="false" viewbox="0 -677 2556 677" aria-hidden="true" style="vertical-align: 0px;"><defs><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-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-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><path id="MJX-98-NCM-N-32" d="M237 666C186 666 143 648 106 612C69 576 50 534 50 483C50 449 75 424 106 424C136 424 161 450 161 480C161 513 137 536 105 536C102 536 100 536 98 535C117 584 161 627 224 627C306 627 352 556 352 470C352 403 318 331 250 255L62 43C49 28 50 29 50 0L421 0L450 180L417 180C409 129 402 100 396 91C391 86 361 84 306 84L139 84L236 179C304 243 390 312 419 365C439 400 449 435 449 470C449 588 357 666 237 666Z"></path></defs><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math" data-latex="\PageIndex{2}" data-semantic-structure="(5 0 1 2 3 4)"><g data-mml-node="TeXAtom" data-mjx-texclass="ORD" data-latex="2}" data-semantic-type="punctuated" data-semantic-role="sequence" 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data-semantic-attributes="latex:11" data-semantic-level-number="1" data-speech-node="true">11</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="2" 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:2" data-semantic-level-number="1" data-speech-node="true">2</mn></mrow></math></mjx-assistive-mml></mjx-container>: Metabolic Pathways</figcaption></figure>

<p class="lt-bio-4648" style="background-color: unset;">Within cells, these molecules are further degraded into still simpler molecules containing two to four carbon atoms. These fragments (<strong>acetyl-CoA</strong> for example) face one of two alternatives. They may proceed up various metabolic pathways and serve as the building blocks of, for example, sugars and fatty acids. From these will be assembled the macromolecules of the cell (e.g., polysaccharides, fats, proteins, and nucleic acids). Alternatively, the molecules in this pool of two- to four-carbon fragments may be still further degraded &mdash; ultimately to simple inorganic molecules such as carbon dioxide (CO<sub><font size="2">2</font></sub>), H<sub><font size="2">2</font></sub>O, and ammonia (NH<sub><font size="2">3</font></sub>). This phase of catabolism releases large amounts of energy (in the form of <strong>ATP</strong>). One use to which this energy is put is to run the anabolic activities of the cell.</p>

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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/04:_Cell_Metabolism/4.11:_Metabolism">4.11: Metabolism</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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