Amino Acids and Ploypeptides
Proteins: Main Agents of Biological Function
• Catalysis
– enolase (in the glycolytic pathway)
– DNA polymerase (in DNA replication)
• Transport
– hemoglobin (transports O2 in the blood)
– lactose permease (transports lactose across the cell membrane)
• Structure
– collagen (connective tissue)
– keratin (hair, nails, feathers, horns)
• Motion
– myosin (muscle tissue)
– actin (muscle tissue, cell motility)
Amino Acids: Building Blocks of Protein
• Proteins are linear heteropolymers of-amino acids
• Amino acids share many features, differing only at the R substituent
• Amino acids have properties that are well-suited to carry out a variety
of biological functions
– Capacity to polymerize
– Useful acid-base properties
– Varied physical properties
– Varied chemical functionality α
All amino acids are chiral (except glycine)
• The-carbon always has four substituents (chiral Center) and is
tetrahedral
, • In glycine, the fourth substituent is also hydrogen
– Glycine-carbon is achiral (non-chiral)
Proteins only contain L amino acids
• Because of the tetrahedral arrangement of the bonding orbitals
around the α –carbon atom, the four different groups can occupy two
unique spatial arrangements, and thus amino acids have two possible
mirror images stereoisomers (called enantiomers, L and D)
Amino Acids: Atom Naming
• Organic nomenclature: start from one end
• Biochemical designation:
– start from-carbon and go down the R-group
Amino Acids: Classification
Common amino acids can be placed in five basic groups depending on
their R substituents:
• Nonpolar, aliphatic (7)
• Aromatic (3)
• Polar, uncharged (5)
• Positively charged (3)
• Negatively charged (2)
Proteins: Main Agents of Biological Function
• Catalysis
– enolase (in the glycolytic pathway)
– DNA polymerase (in DNA replication)
• Transport
– hemoglobin (transports O2 in the blood)
– lactose permease (transports lactose across the cell membrane)
• Structure
– collagen (connective tissue)
– keratin (hair, nails, feathers, horns)
• Motion
– myosin (muscle tissue)
– actin (muscle tissue, cell motility)
Amino Acids: Building Blocks of Protein
• Proteins are linear heteropolymers of-amino acids
• Amino acids share many features, differing only at the R substituent
• Amino acids have properties that are well-suited to carry out a variety
of biological functions
– Capacity to polymerize
– Useful acid-base properties
– Varied physical properties
– Varied chemical functionality α
All amino acids are chiral (except glycine)
• The-carbon always has four substituents (chiral Center) and is
tetrahedral
, • In glycine, the fourth substituent is also hydrogen
– Glycine-carbon is achiral (non-chiral)
Proteins only contain L amino acids
• Because of the tetrahedral arrangement of the bonding orbitals
around the α –carbon atom, the four different groups can occupy two
unique spatial arrangements, and thus amino acids have two possible
mirror images stereoisomers (called enantiomers, L and D)
Amino Acids: Atom Naming
• Organic nomenclature: start from one end
• Biochemical designation:
– start from-carbon and go down the R-group
Amino Acids: Classification
Common amino acids can be placed in five basic groups depending on
their R substituents:
• Nonpolar, aliphatic (7)
• Aromatic (3)
• Polar, uncharged (5)
• Positively charged (3)
• Negatively charged (2)
