<h2 data-type="title">RNA</h2>
<p>Ribonucleic acid, or RNA, is mainly involved in the process of protein synthesis under the direction of DNA. RNA is usually single-stranded and is made of ribonucleotides that are linked by phosphodiester bonds. A ribonucleotide in the RNA chain contains ribose (the pentose sugar), one of the four nitrogenous bases (A, U, G, and C), and the phosphate group.</p>
<h2>Types of RNA</h2>
<p>There are four major types of RNA:</p>
<ul>
<li>messenger RNA (mRNA),</li>
<li>ribosomal RNA (rRNA),</li>
<li>transfer RNA (tRNA), and</li>
<li>microRNA (miRNA).</li>
</ul>
<h3>Messenger RNA (mRNA)</h3>
<p>The first, <strong>mRNA</strong>, carries the message from DNA, which controls all of the cellular activities in a cell. If a <a data-lesson="introduction-to-cell-reproduction" data-subject="biology" data-tutorial="cell-reproduction" href="https://app.ulearngo.com/biology/cell-reproduction/introduction-to-cell-reproduction">cell</a> requires a certain protein to be synthesized, the gene for this product is turned <em>on</em>. Then, the messenger RNA is synthesized in the nucleus. The RNA base sequence is complementary to the coding sequence of the DNA from which it has been copied. However, in RNA, the base T is absent and U is present instead. If the DNA <a data-lesson="dna-double-helix-structure" data-subject="biology" data-tutorial="biological-macromolecules" href="https://app.ulearngo.com/biology/biological-macromolecules/dna-double-helix-structure">strand</a> has a sequence AATTGCGC, the sequence of the complementary RNA is UUAACGCG. In the cytoplasm, the mRNA interacts with ribosomes and other cellular machinery (see image below).</p>
<div class="wp-caption alignnone" id="attachment_95360" style="width: 544px"><a href="https://data.ulearngo.com/assets/708f9a08-f987-41a0-bc86-6fad8014f7c0"><img alt="ribosome" class="size-full wp-image-95360" height="260" src="https://data.ulearngo.com/assets/708f9a08-f987-41a0-bc86-6fad8014f7c0" width="544"/></a><p class="wp-caption-text">A ribosome has two parts: a large subunit and a small subunit. The mRNA sits in between the two subunits. A tRNA molecule recognizes a codon on the mRNA, binds to it by complementary base pairing, and adds the correct amino acid to the growing peptide chain. Image Attribution: OpenStax Biology</p></div>
<h3>Ribosomal RNA (rRNA)</h3>
<p>The mRNA is read in sets of three bases which we refer to as <strong>codons</strong>. Basically, each codon codes for a single amino acid. In this way, the mRNA is read and the protein product is made. <strong>Ribosomal RNA (rRNA)</strong> is a major constituent of ribosomes on which the mRNA binds. The rRNA ensures the proper alignment of the mRNA and the ribosomes. Furthermore, the rRNA of the ribosome also has an enzymatic activity (peptidyl transferase) and catalyzes the formation of the peptide <a data-lesson="hydrogen-bonds-and-van-der-waals-interactions" data-subject="biology" data-tutorial="chemical-foundation-of-life" href="https://app.ulearngo.com/biology/chemical-foundation-of-life/hydrogen-bonds-and-van-der-waals-interactions">bonds</a> between two aligned amino acids.</p>
<h3>Transfer RNA (tRNA)</h3>
<p><strong>Transfer RNA (tRNA)</strong> is one of the smallest of the four types of RNA. It is usually 70–90 nucleotides long. In addition, it carries the correct amino acid to the site of protein synthesis. As a matter of fact, it is the base pairing between the tRNA and mRNA that allows for the insertion of the correct amino acid in the polypeptide chain.</p>
<h3>microRNA (miRNA)</h3>
<p>microRNAs are the smallest RNA molecules. Their role involves the <a data-lesson="regulation-of-gene-expression" data-subject="biology" data-tutorial="gene-expression" href="https://app.ulearngo.com/biology/gene-expression/regulation-of-gene-expression">regulation of gene expression</a> by interfering with the expression of certain mRNA messages.</p>
<h2>Features of DNA and RNA</h2>
<p>The table below summarizes features of DNA and RNA.</p>
<table id="tab-ch03-05-01" summary="">
<thead>
<tr>
<th colspan="3" data-align="left" scope="col">Features of DNA and RNA</th>
</tr>
<tr>
<th scope="col"> </th>
<th scope="col">DNA</th>
<th scope="col">RNA</th>
</tr>
</thead>
<tbody>
<tr>
<td>Function</td>
<td>Carries genetic information</td>
<td>Involved in protein synthesis</td>
</tr>
<tr>
<td>Location</td>
<td>Remains in the nucleus</td>
<td>Leaves the nucleus</td>
</tr>
<tr>
<td>Structure</td>
<td>Double helix</td>
<td>Usually single-stranded</td>
</tr>
<tr>
<td>Sugar</td>
<td>Deoxyribose</td>
<td>Ribose</td>
</tr>
<tr>
<td>Pyrimidines</td>
<td>Cytosine, thymine</td>
<td>Cytosine, uracil</td>
</tr>
<tr>
<td>Purines</td>
<td>Adenine, guanine</td>
<td>Adenine, guanine</td>
</tr>
</tbody>
</table>
<p id="fs-id1569149">Even though the RNA is single stranded, most RNA types show extensive intramolecular base pairing between complementary sequences, creating a predictable three-dimensional structure essential for their function.</p>
<h3>Transcription and Translation</h3>
<p id="fs-id1438288">As you have learned, information flow in an organism takes place from DNA to RNA to protein. DNA dictates the structure of mRNA in a process known as <strong>transcription</strong>, and RNA dictates the structure of protein in a process known as <strong>translation</strong>. This is known as the Central Dogma of Life, which holds true for all organisms. However, exceptions to the rule occur in connection with viral infections.</p>
<h2>Video Summarizing Nucleic Acids</h2>
<p>This short video below by <a href="http://ricochetscience.com">Ricochet Science</a> describes the structure and function of nucleic acids.</p>
<p><iframe allowfullscreen="allowfullscreen" frameborder="0" height="360" src="https://www.youtube.com/embed/MA-ouz1LtpM?rel=0&amp;modestbranding=1&amp;cc_lang_pref=en&amp;cc_load_policy=1" width="640"></iframe></p>

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Types and Functions of RNA

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Discover the different types and functions of biological macromolecules including carbohydrates, lipids, proteins, and nucleic acids, and explore their structures and synthesis through lessons on hydrolysis, disaccharides, protein structures, and DNA double-helix.


Types and Functions of RNA

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