Amino Acids & Chemical Evolution of Proteins

68 Pages·2012·0.89 MB·English

Amino Acids
Introduction
• Amino Acids of Proteins
a. General Properties
b. Peptide Bonds
c. Classification & Characterization
d. Acid – Base Properties
e. A Few Words on Nomenclature
Introduction, Cont.
• Optical Activity
a. An Operational Classification
b. The Fisher Convention
c. The Cahn – Ingold – Prelog System
d. Chirality and Biochemistry
Introduction, Cont.
• Nonstandard Amino Acids
a. Amino Acid Derivatives in Proteins
b. Specialized Roles of Amino Acids
Introduction, Cont.
• Chemical Evolution
a. Sickle Cell Anemia: The Influence of
Natural Selection
b. Species Variation in Homologous
Proteins: The Effect of Neutral Drift
c. Evolution Through Gene Duplication
Amino Acids of Proteins

General Properties
• pK Values of the 20 Standard
- pK refer to the α – Carboxylic Acid
1
- pK refer to the α – Amino Groups
2
- pK refer to the Side Groups with Acid-Base
R
Properties

What is pK ?!
Amino Acids of Proteins

General Properties, Cont.
• In chemistry and Biochemistry, a
Dissociation Constant or an Ionization
Constant is a Specific Type of Equilibrium
Constant Used for Reversible Reactions or
Processes

The pK Value is Defined as:
pK = - log K
d
Amino Acids of Proteins

General Properties, Cont.
• α – Carboxylic Acid Groups lie in small
range 2.2
• Above pH 3.5 These Groups are almost
Entirely in Their Carboxylate Forms
• α – Amino Groups All Have pK Values
Near 9.4
• Below pH 8.0 These Groups are almost
Entirely in Their Ammonium Ion Forms
Amino Acids of Proteins

General Properties, Cont

In the physiological pH Range, Both
the Carboxylic Acid and the Amino
Groups of α – Amino Acids are
Completely Ionized
Amino Acids of Proteins

General Properties, Cont

The Amino Acids Plays a Role as a Buffer