Notes
Amino Acids - Structural Classification
Let's start with their structural classification, which we explore in detail elsewhere.
- Show that amino acids have a general structure of a central carbon (the alpha carbon) with four different atoms or groups bound to it.
- Hydrogen
- Carboxylic acid (COOH) group
- Amino (NH2) group
- Variable, R, group
- Denote that via this organization we can divide the amino acids into four general structural categories:
#Let's look at each of these categories in some detail.
#First, the hydrophobic amino acids, which are so-named because they have nonpolar side chains. As a reminder, nonpolar means that the electrons in the bond are shared equally – these typically involve carbon-carbon or carbon-hydrogen bonds.
- Point out the following clinically-relevant nonpolar, branched chain amino acids: valine, isoleucine, and leucine.
- To solidify what we mean by this, draw a central carbon, an amino group, carboxylic acid, (leave out the hydrogen in this stick-figure format) and show a prototypical branched chain.
- Now, indicate the aromatic amino acids, show that their R group incorporates an aromatic ring.
- Next, include the polar group, so-named because they are hydrophilic – meaning electrons are unequally share along the polar bond.
- Now, the charged group.
- Specify that ACIDIC amino acids have a negative charge at physiologic pH.
- Indicate that they are aspartate (thus called aspartic acid) and glutamate (thus called glutamic acid).
- Specify that the BASIC amino acids have a positive charge at physiologic pH.
- Indicate that they are Lysine and Arginine (and sometimes Histidine – thus, you'll see it listed as charged or uncharged in differing resources).
- Finally, the special cases:
- Glycine (which essentially has NO side chain – just a hydrogen, thus it is achiral)
- Proline (which forms has a particularly unfavorable chain: an imino ring – the side chain is connected to the protein backbone).