#03 Biochemistry Amino Acids Lecture for Kevin Ahern's BB 450/550

Two BIG new items for pre-meds! Lecture Highlights 1. Molecules can have more than one buffering region. Alanine, for example has both an amine group and a carboxyl group that can gain/lose protons (hydrogen ions). It will thus have two pKas, one for the carboxyl group and one for the amine group. 2. A buffer system will be at maximum capacity when the concentration of the undissociated acid (HA) equals that of the salt (A-)- (Acid = Salt). The Henderson Hasselbalch equation further reveals that when this is true, pH = pKa. 3. Amine systems (also in amino acids) have two forms NH3+ and NH2. Note that the NH3+ is the acid and NH2 is the salt in my nomenclature. Carboxyl systems have two forms too. COOH has no charge and when it loses its proton, COO- has a negative one charge. 4. Students make mistakes calling things acids and bases. Carboxyl groups are acidic and most think of amine groups as basic. Consequently, they get confused when they think of an amine like NH3+ donating protons (acting like an acid). The same students usually aren&confused, however, about COO- accepting protons (acting like a base). That is why I avoid calling amine groups "bases". 5. The Henderson Hasselbalch equation tells us we can predict the ratio of salt to acid as a function of pH if we know the pKa. Consequently, we can predict the charge on amino acids in a protein as the pH changes. Subtle changes in pH in the body can have drastic changes in protein structure and function. 1. Protein...