Quaternary structures are not found in every protein. Quaternary structure refers to the variable group interactions between different polypeptides to form a single larger protein. Quaternary Structure of a 3-D Multi-Polypeptide Protein Many students confuse this with secondary structure, which is only backbone interactions. Let me repeat myself, tertiary structure is the first time you’ll see variable R-group side chain interactions on the polypeptide chain. THIS is where knowledge and understanding of amino acid side chains are critical. The tertiary structure is where the real 3-dimensional folding is introduced, and this is the first time you’ll notice side-chain interactions. The secondary structure of alpha helix and beta pleated sheets come from hydrogen bonding between the partially negative oxygen on the carbonyl and the partially positive hydrogen on the nitrogen. The peptide bond turns every former carboxyl and amino group into an amide functional group. The secondary structure comes from backbone hydrogen bonding interactions. If the polypeptide chain is attached in a different order, you get a very different overall structure. The first and more important determination factor of protein structure is the sequence of amino acids. In a biological system structure determines function, so understanding amino acid characteristics is key to understanding structure and ultimately protein function.
One final concept before we break down the individual amino acids, and that is the 3-dimensional protein structure. More on zwitterion and amino acid charges in my next article (link to follow). Since the carboxyl group is acidic and the amino group basic, the two will exist as a zwitterion in their conjugated charged forms in physiological pH. While the fully-neutral version above is how most students study amino acids, and the form we’ll use in this article, keep in mind that this is technically incorrect. They range from a simple hydrogen atom (glycine) to a complex 2-ring resonating aromatic system (tryptophan). There are 20 different amino acids distinguished by their unique side chains. Finally we have the R group (red), which is a variable side chain. Attached to the central carbon you have a hydrogen atom (gray), an amino or NH2 group (green), and a carboxylic acid COOH group (purple). The amino acid has a central chiral carbon called the alpha carbon (black). The amino acid gets its name from its two primary functional groups.
You need to actively tackle each amino acid individually.įor a quick reference list download my free Amino Acid Cheat Sheet Study Guide But don’t simply stick the words and structures onto flashcards hoping to force it into your memory.
This includes the side chain, full name, 3-letter name and single letter abbreviation. The MCAT requires understanding the nature of polar and nonpolar side chains and the twisting and conformations caused by hydrophobic and hydrophilic interactionsĪnd yes, you should be memorizing each amino acid for the MCAT. The complexity of a protein structure is determined by its sequence of amino acids and the chemical nature of their variable group side chains. But then you have your workers, transportation system and the very structure of the cell city, which are all made of proteins- which in turn are made of amino acids. I like to think of the cell as a self contained city where the nucleus is the capital, the mitochondria is the power plant and so on. Long chains of amino acids make up proteins, which in turn make up many structural and functional cell components. Amino acids are the building blocks of living things.