Section 2 - Protein Composition and Structure
Chapter 3 - Amino Acids
● Fischer Projection: every atom is identified and the bonds to the central carbon atom
are represented by horizontal and vertical lines
● Stereochemistry
3.1 - Proteins Are Built from a Repertoire of 20 Amino Acids
● α-amino acids
○ Central carbon atom → α-carbon
○ Amino group
○ Carboxylic acid group
○ Hydrogen atom
○ Side chain → R group
● Chiral: they may exist in one or the other of two mirror-image forms
○ L isomer
■ Constituents of proteins
○ D isomer
● Free amino acids in solution at neutral pH exist predominantly as Dipolar ions
(Zwitterions)
○ Amino group is pronated (NH3+)
○ The Carboxyl group is depronated (COO-)
● Acid solution
, ○ Amino group is pronated (NH3+)
○ The Carboxyl group is not dissociated (-COOH)
3.2 - Amino Acids Contain a Wide Array of Functional Groups
● 4 Groups of amino acids based on the general characteristics of their R groups
○ Hydrophobic amino acids with nonpolar R groups
■ Side chains consisting only of hydrogen and carbon
Chapter 3 - Amino Acids
● Fischer Projection: every atom is identified and the bonds to the central carbon atom
are represented by horizontal and vertical lines
● Stereochemistry
3.1 - Proteins Are Built from a Repertoire of 20 Amino Acids
● α-amino acids
○ Central carbon atom → α-carbon
○ Amino group
○ Carboxylic acid group
○ Hydrogen atom
○ Side chain → R group
● Chiral: they may exist in one or the other of two mirror-image forms
○ L isomer
■ Constituents of proteins
○ D isomer
● Free amino acids in solution at neutral pH exist predominantly as Dipolar ions
(Zwitterions)
○ Amino group is pronated (NH3+)
○ The Carboxyl group is depronated (COO-)
● Acid solution
, ○ Amino group is pronated (NH3+)
○ The Carboxyl group is not dissociated (-COOH)
3.2 - Amino Acids Contain a Wide Array of Functional Groups
● 4 Groups of amino acids based on the general characteristics of their R groups
○ Hydrophobic amino acids with nonpolar R groups
■ Side chains consisting only of hydrogen and carbon
