Draw a schematic of the chemical structure of the Leu-Tyr-Met-Lys tetrapeptide, with the correct ionization at neutral pH (pH 7). Also, give an estimate the pl of this tetrapeptide (you are given that the pKa of any acidic R group is 4, the pKa of any basic R group is 11.5, and the pKa of the α-COOH is 2, and the a-NH3 is 9.5). Provide rationale!

Consider a protein in which a negatively charged glutamic acid side chain (pKa=4.2) makes a salt bridge (ion-ion interaction) with a positively charged histidine side chain (pKa=6.5). Part C: Justify your answer with calculations of partial charges on these amino acid side chains at pH=7.9.(Hint: Consider lessons from Coulomb's law, and the Henderson-Hasselbalch equation.)

Phosphate buffers are commonly used to mimic biological systems. Given that phosophoric acid is a triprotic acid with three pKas (2.12, 7.21, and 12.32), why do you think this is? What are the dominant buffering compounds present in a phosphate buffer near physiological pH?

The amino acid glycine is often used as an ingredient in buffers for biochemistry experiments. The amino group of glycine has a pKa of 9.6. Glycine exists in either a protonated form (-NH3+) or a free base (-NH₂). a) In what pH range can glycine be used as an effective buffer? b) In a 0.1M solution of glycine at pH 9.0, what fraction has its amino group in the protonated form? c) When 99% of the glycine is in the protonated from, what is the numerical relation between the pH of the solution and the pKa of the amino group?