<p>Can someone explain to me the concept of protein structure levels (primary, secondary, tertiary, quarternary)? I encountered this in Kaplan’s book and I really do not understand the concept. Also, is something this trivial even going to be tested?</p>
<p>Thanks in advance!</p>
<p>Well its basically how proteins are arranged. This is important because it governs the properties of that particular protein. </p>
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<p>Look at it this way. If an amino acid is a magnetized lego brick, then the primary structure is what order (e.g. color) are the bricks arranged in. Okay, so now you build you’re column of lego bricks in a specific sequence of color. </p>
<p>But since each brick is magnetic, the columns you just built bends and twists weirdly in their own way—that’s secondary structure. </p>
<p>Now you join the weird columns you built. But once they’re joined, the magnetic interactions causes the whole shape of the thing to twist weirdly. So tertiary structure is how the big, big piece interacts with one another. </p>
<p>You then decide to combine your big ass lego thing with your friend’s—quaternary structure. This structure depends on which friend you join to…</p>
<p>Hmmm, this is probably a bad analogy :/</p>
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<p>Here’s a deeper explanation if you care to read:</p>
<p>1. Primary structure - the sequence of amino acid. </p>
<p>This will directly determine what protein it IS. So this structure is the basis of all protein. </p>
<p>2. Secondary structure - how the polypeptide chain (chain of amino acids) folds and bends. </p>
<p>This is often caused by the Hydrogen bonds formed between each amino acid (the amino and the carboxyl group). So the attraction causes the chain to spiral (alpha helix) or fold (beta pleating) or simply form an open loop.</p>
<p>3. Tertiary structure - This is how the secondary structure (the protein), folds on itself. This is govern by the R-groups each amino acid has. </p>
<p>If the R-groups of two amino acids contain sulfur, it can form a covalent bond. If they’re non-polar, then they are affected by hydrophobic interactions (repel water; which could mean they like to hide inside the protein rather than facing the water molecules outside). If they’re polar, then they could possibly form hydrogen bonds, or ionic bonds if they’re ionic. </p>
<p>Basically the overall 3D shape of the protein depends on how the R-groups interact with one another.</p>
<p>4. Quaternary - How the tertiary structure comes together, i.e. small protein chains join forces to become an even bigger one. For example, a haemoglobin is composed of four smaller proteins.</p>
<p>Wow, thanks!</p>