1.05:_Hydrogen_Bonds

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<span id="Hydrogen_Bonds"></span><span id="Hydrogen_Bonds"></span><h2 style="background-color: unset;" class="lt-bio-3745">Hydrogen Bonds</h2>

<p class="lt-bio-3745" style="background-color: unset;">Polar molecules, such as water molecules, have a weak, partial negative charge at one region of the molecule (the oxygen atom in water) and a partial positive charge elsewhere (the hydrogen atoms in water). Thus when water molecules are close together, their positive and negative regions are attracted to the oppositely-charged regions of nearby molecules. The force of attraction, shown here as a dotted line, is called a <strong>hydrogen bond</strong>. Each water molecule is hydrogen bonded to four others.</p>

<p class="lt-bio-3745" style="background-color: unset;">The hydrogen bonds that form between water molecules account for some of the essential &mdash; and unique &mdash; properties of water.</p>

<ul>
    <li class="lt-bio-3745" style="background-color: unset;">The attraction created by hydrogen bonds keeps water liquid over a wider range of temperature than is found for any other molecule its size.</li>
    <li class="lt-bio-3745" style="background-color: unset;">The energy required to break multiple hydrogen bonds causes water to have a high heat of vaporization; that is, a large amount of energy is needed to convert liquid water, where the molecules are attracted through their hydrogen bonds, to water vapor, where they are not.</li>
</ul>

<p class="lt-bio-3745" style="background-color: unset;">Two outcomes of this:</p>

<ul>
    <li class="lt-bio-3745" style="background-color: unset;">The evaporation of sweat, used by many mammals to cool themselves, cools by the large amount of heat needed to break the hydrogen bonds between water molecules.</li>
    <li class="lt-bio-3745" style="background-color: unset;">Reduction of temperature extremes near large bodies of water like the ocean.</li>
</ul>

<p class="lt-bio-3745" style="background-color: unset;">The hydrogen bond has only 5% or so of the strength of a covalent bond. However, when many hydrogen bonds can form between two molecules (or parts of the same molecule), the resulting union can be sufficiently strong as to be quite stable.</p>

<p class="lt-bio-3745" style="background-color: unset;">Multiple hydrogen bonds</p>

<ul>
    <li class="lt-bio-3745" style="background-color: unset;">hold the two strands of the DNA double helix together</li>
    <li class="lt-bio-3745" style="background-color: unset;">hold polypeptides together in such secondary structures as the alpha helix and the beta conformation</li>
    <li class="lt-bio-3745" style="background-color: unset;">help enzymes bind to their substrate</li>
    <li class="lt-bio-3745" style="background-color: unset;">help antibodies bind to their antigen</li>
    <li class="lt-bio-3745" style="background-color: unset;">help transcription factors bind to each other</li>
    <li class="lt-bio-3745" style="background-color: unset;">help transcription factors bind to DNA</li>
</ul>

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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/01:_The_Chemical_Basis_of_Life/1.05:_Hydrogen_Bonds">1.5: Hydrogen Bonds</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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