<h2>Summary of lessons so far</h2>
<p>Proteins are a class of macromolecules that perform a diverse range of functions for the cell. They help in <a data-lesson="metabolism" data-subject="biology" data-tutorial="protists" href="https://app.ulearngo.com/biology/protists/metabolism">metabolism</a> by providing structural support and by acting as enzymes, carriers, or hormones.</p>
<p>The building blocks of <a data-lesson="proteins-2" data-subject="biology" data-tutorial="biology-foundations" href="https://app.ulearngo.com/biology/biology-foundations/proteins-2">proteins</a> (monomers) are amino acids. Each amino acid has a central <a data-lesson="carbon-cycle" data-subject="biology" data-tutorial="ecology-overview" href="https://app.ulearngo.com/biology/ecology-overview/carbon-cycle">carbon</a> that linked to an amino group, a carboxyl group, a hydrogen atom, and an R group or side chain. There are 20 commonly occurring amino acids, each of which differs in the R group. Each amino acid links to its neighbors by a peptide bond. We refer to a long chain of amino acids as a polypeptide.</p>
<p>The organization of proteins occurs at four levels: primary, secondary, tertiary, and (optional) quaternary. The primary structure is the unique sequence of amino acids. The local folding of the polypeptide to form structures such as the <em data-effect="italics">α-</em>helix and <em data-effect="italics">β</em>-pleated sheet constitutes the secondary structure. The overall three-dimensional structure is the tertiary structure. When two or more polypeptides combine to form the complete protein structure, the configuration is known as the quaternary structure of a protein (<a href="#attachment_95348">see image below</a>).</p>
<div class="wp-caption alignnone" id="attachment_95348" style="width: 800px"><a href="https://data.ulearngo.com/assets/5e5dda31-e512-4b43-baa3-83cf1f1ab12b"><img alt="protein-structure" class="size-full wp-image-95348" height="600" src="https://data.ulearngo.com/assets/5e5dda31-e512-4b43-baa3-83cf1f1ab12b" width="800"/></a><p class="wp-caption-text">Note that the primary structure here illustrates the amino acids using abbreviations of their names. For example, <em>Lys</em> stands for <em>Lysine</em>, <em>Gly</em> stands for <em>Glycine</em>, and so on. Image Attribution: "Holger87" / Wikimedia Commons (<a href="https://creativecommons.org/licenses/by-sa/3.0/deed.en">CC BY-SA 3.0</a>)</p></div>
<p>Protein shape and function are intricately linked. In fact, any change in shape caused by changes in temperature or pH may lead to protein denaturation and a loss in function.</p>
<h2>Glossary of Words</h2>
<h3>Alpha-helix structure (<em data-effect="italics">α</em>-helix)</h3>
<p>type of <a data-lesson="secondary-structure-proteins" data-subject="biology" data-tutorial="biological-macromolecules" href="https://app.ulearngo.com/biology/biological-macromolecules/secondary-structure-proteins">secondary structure of proteins</a> formed by folding of the polypeptide into a helix shape with <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">hydrogen bonds</a> stabilizing the structure</p>
<h3>Amino acid</h3>
<p>monomer of a protein; has a central carbon or alpha carbon to which an amino group, a carboxyl group, a hydrogen, and an R group or side chain is attached; the R group is different for all 20 amino acids</p>
<h3>Beta-pleated sheet (<em data-effect="italics">β</em>-pleated)</h3>
<p>secondary structure found in proteins in which “pleats” are formed by hydrogen bonding between <a data-lesson="chemical-reactions-molecules" data-subject="biology" data-tutorial="chemical-foundation-of-life" href="https://app.ulearngo.com/biology/chemical-foundation-of-life/chemical-reactions-molecules">atoms</a> on the backbone of the polypeptide chain</p>
<h3>Chaperone</h3>
<p>(also, chaperonin) protein that helps nascent protein in the folding process</p>
<h3>Denaturation</h3>
<p>loss of shape in a protein as a result of changes in temperature, pH, or exposure to chemicals</p>
<h3>Enzyme</h3>
<p>catalyst in a biochemical reaction; usually a complex or conjugated protein</p>
<h3>Hormone</h3>
<p>chemical <a data-lesson="forms-of-signaling" data-subject="biology" data-tutorial="cell-communication" href="https://app.ulearngo.com/biology/cell-communication/forms-of-signaling">signaling</a> molecule, usually protein or steroid, secreted by endocrine <a data-lesson="prokaryotic-and-eukaryotic-cells" data-subject="biology" data-tutorial="cell-biology" href="https://app.ulearngo.com/biology/cell-biology/prokaryotic-and-eukaryotic-cells">cells</a> that act to control or regulate specific physiological processes</p>
<h3>Peptide bond</h3>
<p>bond formed between two amino acids by a dehydration reaction</p>
<h3>Polypeptide</h3>
<p>long chain of amino acids linked by peptide bonds</p>
<h3>Primary structure</h3>
<p>linear sequence of amino acids in a protein</p>
<h3>Protein</h3>
<p>biological macromolecule composed of one or more chains of amino acids</p>
<h3>Quaternary structure</h3>
<p>association of discrete polypeptide subunits in a protein</p>
<h3>Secondary structure</h3>
<p>regular structure formed by proteins by intramolecular hydrogen bonding between the <a data-lesson="transport-of-oxygen-in-the-blood" data-subject="biology" data-tutorial="respiratory-system" href="https://app.ulearngo.com/biology/respiratory-system/transport-of-oxygen-in-the-blood">oxygen</a> atom of one amino acid residue and the hydrogen attached to the <a data-lesson="nitrogen-cycle" data-subject="biology" data-tutorial="ecology-overview" href="https://app.ulearngo.com/biology/ecology-overview/nitrogen-cycle">nitrogen</a> atom of another amino acid residue</p>
<h3>Tertiary structure</h3>
<p>three-dimensional conformation of a protein, including interactions between secondary structural elements; formed from interactions between amino acid side chains</p>

ad260561-7f24-4cf8-a3f2-b129f5e47c91

Summarizing Proteins

Biology studies life and living organisms. Biology can be divided into different sections that cover the morphology, physiology, anatomy, behavior, and so on of living organisms.

Biology

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.


Summarizing Proteins

Track Your Learning Progress