Lecture 2

The conjugate acid with the lowest pka co2 buffering

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Unformatted text preview: Buffering Lungs WHAT ARE AMINO ACIDS? Blood H+ CO3-2 HCO3 CO2 + H2 O <-> H2CO3 α−amino acids H+ H+ Blood H+ COOpKa ~3 NH3+ Cα H pKa ~9 R zwitter ion Carboxylate α−Amino α R group Serine, Ser, S You will need to know the structures, 3-letter and 1-letter abbreviation, and the charge at different pHs for all 20 amino acids. 2 Titrating a zwitter ion (2 p Ka’ s) O +1 pKa (COOH) OH H+ C +H 3N C O O- +H 3N C H CH3 H+ pKa (NH3 ) O H+ C H CH3 0 Fig 3.6 (pg 63) Titration curve for alanine -1 O- C H2N H+ C CH3 H • Titration curves are used to determine pKa values • pK1 = 2.4 • pK2 = 9.9 • pIAla = isoelectric point (pI = pH when net charge is zero) Increasing pH pI = (2.4+9.9) / 2 = 6.15 Amino acids are asymmetric-they have a c hiral c enter (except glycine). They can exist as e nantiomers. Serine, Ser, S O- O C +H 3N Cα H CH2 β L-Serine OH γ Greek letters = α, β, γ, δ, ε, ζ, η Alternate = a, b, g, d, e, z, h D-Serine C OO NH3 + C H R Figure 3.2, Horton Functional R-Groups L-Serine CO N NH3+ NH2 R R Alcohol Cα SH O OH O- O S- R R NH2 C Thiol C R R Amine Fischer Projection Carboxamide R Carboxylate NH HN HN Fischer Projection C OO NH3 + C H R “CORN” R H2N NH2 H2N NH2 C NH+ NH+ NH+ N C R “CORN” R R R R Indole Imidazole Guanidinium 3 Table 3.1 H ydropathy s cale for amino acid residues Four Aliphatic Amino Acid Structures 3N C H +H 3N C H +H...
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