2.07:_Amino_Acids

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<p class="lt-bio-3785" style="background-color: unset;">Amino acids are the building blocks (monomers) of proteins. 20 different amino acids are used to synthesize proteins. The <strong>shape</strong> and other properties of each protein is dictated by the precise sequence of amino acids in it.</p>

<p class="lt-bio-3785" style="background-color: unset;">Each amino acid consists of an <strong>alpha carbon atom</strong> to which is attached</p>

<ul>
    <li class="lt-bio-3785" style="background-color: unset;">a hydrogen atom</li>
    <li class="lt-bio-3785" style="background-color: unset;">an amino group (hence &quot;amino&quot; acid)</li>
    <li class="lt-bio-3785" style="background-color: unset;">a carboxyl group (-COOH). This gives up a proton and is thus an <a href="http://biology-pages.info/A/Acids_Bases.html" target="_blank" rel="external noopener nofollow" class="external">acid</a> (hence amino &quot;acid&quot;)</li>
    <li class="lt-bio-3785" style="background-color: unset;">one of 20 different &quot;R&quot; groups. It is the structure of the R group that determines which of the 20 it is and its special properties. The amino acid shown here is <strong>Alanine</strong></li>
</ul>

<table class="mt-responsive-table" align="center">
    <caption>Table 2.7.1: Types of Amino Acids. For each amino acid both three-letter and single letter codes are given </caption>
    <thead>
        <tr>
            <th class="mt-align-center" scope="col" style="vertical-align:middle;">Alanine</th>
            <th class="mt-align-center" scope="col" style="vertical-align:middle;">Ala</th>
            <th class="mt-align-center" scope="col" style="vertical-align:middle;">A</th>
            <th class="mt-align-center" scope="col" style="vertical-align:middle;">hydrophobic</th>
        </tr>
    </thead>
    <tbody>
        <tr>
            <td class="mt-align-center lt-bio-3785" data-th="Alanine" style="vertical-align: middle; background-color: unset;">Arginine</td>
            <th class="mt-align-center " data-th="Ala" style="vertical-align:middle;">Arg</th>
            <th class="mt-align-center " data-th="A" style="vertical-align:middle;">R</th>
            <td class="mt-align-center  lt-bio-3785" data-th="hydrophobic" style="vertical-align: middle; background-color: unset;">free amino group makes it basic and hydrophilic</td>
        </tr>
        <tr>
            <td class="mt-align-center lt-bio-3785" data-th="Alanine" style="vertical-align: middle; background-color: unset;">Asparagine</td>
            <th class="mt-align-center " data-th="Ala" style="vertical-align:middle;">Asn</th>
            <th class="mt-align-center " data-th="A" style="vertical-align:middle;">N</th>
            <td class="mt-align-center  lt-bio-3785" data-th="hydrophobic" style="vertical-align: middle; background-color: unset;">carbohydrate can be covalently linked (&quot;N-linked) to its -NH</td>
        </tr>
        <tr>
            <td class="mt-align-center lt-bio-3785" data-th="Alanine" style="vertical-align: middle; background-color: unset;">Aspartic acid</td>
            <th class="mt-align-center " data-th="Ala" style="vertical-align:middle;">Asp</th>
            <th class="mt-align-center " data-th="A" style="vertical-align:middle;">D</th>
            <td class="mt-align-center  lt-bio-3785" data-th="hydrophobic" style="vertical-align: middle; background-color: unset;">free carboxyl group makes it acidic and hydrophilic</td>
        </tr>
        <tr>
            <td class="mt-align-center lt-bio-3785" data-th="Alanine" style="vertical-align: middle; background-color: unset;">Cysteine</td>
            <th class="mt-align-center " data-th="Ala" style="vertical-align:middle;">Cys</th>
            <th class="mt-align-center " data-th="A" style="vertical-align:middle;">C</th>
            <td class="mt-align-center  lt-bio-3785" data-th="hydrophobic" style="vertical-align: middle; background-color: unset;">oxidation of their sulfhydryl (-SH) groups link 2 Cys (S-S)</td>
        </tr>
        <tr>
            <td class="mt-align-center lt-bio-3785" data-th="Alanine" style="vertical-align: middle; background-color: unset;">Glutamic acid</td>
            <th class="mt-align-center " data-th="Ala" style="vertical-align:middle;">Glu</th>
            <th class="mt-align-center " data-th="A" style="vertical-align:middle;">E</th>
            <td class="mt-align-center  lt-bio-3785" data-th="hydrophobic" style="vertical-align: middle; background-color: unset;">free carboxyl group makes it acidic and hydrophilic</td>
        </tr>
        <tr>
            <td class="mt-align-center lt-bio-3785" data-th="Alanine" style="vertical-align: middle; background-color: unset;">Glutamine</td>
            <th class="mt-align-center " data-th="Ala" style="vertical-align:middle;">Gln</th>
            <th class="mt-align-center " data-th="A" style="vertical-align:middle;">Q</th>
            <td class="mt-align-center  lt-bio-3785" data-th="hydrophobic" style="vertical-align: middle; background-color: unset;">moderately hydrophilic</td>
        </tr>
        <tr>
            <td class="mt-align-center lt-bio-3785" data-th="Alanine" style="vertical-align: middle; background-color: unset;">Glycine</td>
            <th class="mt-align-center " data-th="Ala" style="vertical-align:middle;">Gly</th>
            <th class="mt-align-center " data-th="A" style="vertical-align:middle;">G</th>
            <td class="mt-align-center  lt-bio-3785" data-th="hydrophobic" style="vertical-align: middle; background-color: unset;">so small it is amphiphilic (can exist in any surroundings)</td>
        </tr>
        <tr>
            <td class="mt-align-center lt-bio-3785" data-th="Alanine" style="vertical-align: middle; background-color: unset;">Histidine</td>
            <th class="mt-align-center " data-th="Ala" style="vertical-align:middle;">His</th>
            <th class="mt-align-center " data-th="A" style="vertical-align:middle;">H</th>
            <td class="mt-align-center  lt-bio-3785" data-th="hydrophobic" style="vertical-align: middle; background-color: unset;">basic and hydrophilic</td>
        </tr>
        <tr>
            <td class="mt-align-center lt-bio-3785" data-th="Alanine" style="vertical-align: middle; background-color: unset;">Isoleucine</td>
            <th class="mt-align-center " data-th="Ala" style="vertical-align:middle;">Ile</th>
            <th class="mt-align-center " data-th="A" style="vertical-align:middle;">I</th>
            <td class="mt-align-center  lt-bio-3785" data-th="hydrophobic" style="vertical-align: middle; background-color: unset;">hydrophobic</td>
        </tr>
        <tr>
            <td class="mt-align-center lt-bio-3785" data-th="Alanine" style="vertical-align: middle; background-color: unset;">Leucine</td>
            <th class="mt-align-center " data-th="Ala" style="vertical-align:middle;">Leu</th>
            <th class="mt-align-center " data-th="A" style="vertical-align:middle;">L</th>
            <td class="mt-align-center  lt-bio-3785" data-th="hydrophobic" style="vertical-align: middle; background-color: unset;">hydrophobic</td>
        </tr>
        <tr>
            <td class="mt-align-center lt-bio-3785" data-th="Alanine" style="vertical-align: middle; background-color: unset;">Lysine</td>
            <th class="mt-align-center " data-th="Ala" style="vertical-align:middle;">Lys</th>
            <th class="mt-align-center " data-th="A" style="vertical-align:middle;">K</th>
            <td class="mt-align-center  lt-bio-3785" data-th="hydrophobic" style="vertical-align: middle; background-color: unset;">strongly basic and hydrophilic</td>
        </tr>
        <tr>
            <td class="mt-align-center lt-bio-3785" data-th="Alanine" style="vertical-align: middle; background-color: unset;">Methionine</td>
            <th class="mt-align-center " data-th="Ala" style="vertical-align:middle;">Met</th>
            <th class="mt-align-center " data-th="A" style="vertical-align:middle;">M</th>
            <td class="mt-align-center  lt-bio-3785" data-th="hydrophobic" style="vertical-align: middle; background-color: unset;">hydrophobic</td>
        </tr>
        <tr>
            <td class="mt-align-center lt-bio-3785" data-th="Alanine" style="vertical-align: middle; background-color: unset;">Phenylalanine</td>
            <th class="mt-align-center " data-th="Ala" style="vertical-align:middle;">Phe</th>
            <th class="mt-align-center " data-th="A" style="vertical-align:middle;">F</th>
            <td class="mt-align-center  lt-bio-3785" data-th="hydrophobic" style="vertical-align: middle; background-color: unset;">very hydrophobic</td>
        </tr>
        <tr>
            <td class="mt-align-center lt-bio-3785" data-th="Alanine" style="vertical-align: middle; background-color: unset;">Proline</td>
            <th class="mt-align-center " data-th="Ala" style="vertical-align:middle;">Pro</th>
            <th class="mt-align-center " data-th="A" style="vertical-align:middle;">P</th>
            <td class="mt-align-center  lt-bio-3785" data-th="hydrophobic" style="vertical-align: middle; background-color: unset;">causes kinks in the chain</td>
        </tr>
        <tr>
            <td class="mt-align-center lt-bio-3785" data-th="Alanine" style="vertical-align: middle; background-color: unset;">Serine</td>
            <th class="mt-align-center " data-th="Ala" style="vertical-align:middle;">Ser</th>
            <th class="mt-align-center " data-th="A" style="vertical-align:middle;">S</th>
            <td class="mt-align-center  lt-bio-3785" data-th="hydrophobic" style="vertical-align: middle; background-color: unset;">carbohydrate can be covalently linked (&quot;O-linked&quot;) to its -OH</td>
        </tr>
        <tr>
            <td class="mt-align-center lt-bio-3785" data-th="Alanine" style="vertical-align: middle; background-color: unset;">Threonine</td>
            <th class="mt-align-center " data-th="Ala" style="vertical-align:middle;">Thr</th>
            <th class="mt-align-center " data-th="A" style="vertical-align:middle;">T</th>
            <td class="mt-align-center  lt-bio-3785" data-th="hydrophobic" style="vertical-align: middle; background-color: unset;">carbohydrate can be covalently linked (&quot;O-linked&quot;) to its -OH</td>
        </tr>
        <tr>
            <td class="mt-align-center lt-bio-3785" data-th="Alanine" style="vertical-align: middle; background-color: unset;">Tryptophan</td>
            <th class="mt-align-center " data-th="Ala" style="vertical-align:middle;">Trp</th>
            <th class="mt-align-center " data-th="A" style="vertical-align:middle;">W</th>
            <td class="mt-align-center  lt-bio-3785" data-th="hydrophobic" style="vertical-align: middle; background-color: unset;">scarce in most plant proteins</td>
        </tr>
        <tr>
            <td class="mt-align-center lt-bio-3785" data-th="Alanine" style="vertical-align: middle; background-color: unset;">Tyrosine</td>
            <th class="mt-align-center " data-th="Ala" style="vertical-align:middle;">Tyr</th>
            <th class="mt-align-center " data-th="A" style="vertical-align:middle;">Y</th>
            <td class="mt-align-center  lt-bio-3785" data-th="hydrophobic" style="vertical-align: middle; background-color: unset;">a phosphate or sulfate group can be covalently attached to its -OH</td>
        </tr>
        <tr>
            <td class="mt-align-center lt-bio-3785" data-th="Alanine" style="vertical-align: middle; background-color: unset;">Valine</td>
            <th class="mt-align-center " data-th="Ala" style="vertical-align:middle;">Val</th>
            <th class="mt-align-center " data-th="A" style="vertical-align:middle;">V</th>
            <td class="mt-align-center  lt-bio-3785" data-th="hydrophobic" style="vertical-align: middle; background-color: unset;">hydrophobic</td>
        </tr>
    </tbody>
</table>

<span id="The_Essential_Amino_Acids"></span><span id="The_Essential_Amino_Acids"></span><h2 style="background-color: unset;" class="lt-bio-3785">The Essential Amino Acids</h2>

<p class="lt-bio-3785" style="background-color: unset;">Humans must include adequate amounts of 9 amino acids in their diet.</p>

<ul>
    <li class="lt-bio-3785" style="background-color: unset;">Histidine</li>
    <li class="lt-bio-3785" style="background-color: unset;">Isoleucine</li>
    <li class="lt-bio-3785" style="background-color: unset;">Leucine</li>
    <li class="lt-bio-3785" style="background-color: unset;">Lysine</li>
    <li class="lt-bio-3785" style="background-color: unset;">Methionine (and/or cysteine)</li>
    <li class="lt-bio-3785" style="background-color: unset;">Phenylalanine (and/or tyrosine)</li>
    <li class="lt-bio-3785" style="background-color: unset;">Threonine</li>
    <li class="lt-bio-3785" style="background-color: unset;">Tryptophan</li>
    <li class="lt-bio-3785" style="background-color: unset;">Valine</li>
</ul>

<p class="lt-bio-3785" style="background-color: unset;">These &quot;essential&quot; amino acids cannot be synthesized from other precursors. However, cysteine can partially meet the need for methionine (they both contain sulfur), and tyrosine can partially substitute for phenylalanine. Two of the essential amino acids, <strong>lysine</strong> and <strong>tryptophan</strong>, are poorly represented in most plant proteins. Thus strict vegetarians should ensure that their diet contains sufficient amounts of these two amino acids. 19 of the 20 amino acids listed above can exist in two forms in three dimensions.</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/02:_The_Molecules_of_Life/2.07:_Amino_Acids">2.7: Amino Acids</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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