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Lecture 2: Amino acids and
Proteins
Amino acids
• Building blocks of proteins
• Can join with other amino acids to build a
peptide
• Peptides with more than 50 amino acids are
called polypeptides
• All amino acids contain nitrogen,oxygen,
carbon and hydrogen
Amino acids
AMINO ACIDS
• Can release H+ from either its carboxylic or
amino end in water
• Can be zwitterionic in nature
• All amino acids are chiral molecules except for
glycine
• Enantiomers are formed (nonsuperimposable
images relative to the chrial center)
AMINO ACIDS
• Optically active – the ability to rotate the plane
of polarization of plane-polarized light
• Clockwise rotation of incident light is
dextrorotatory while the counter clockwise
rotation is levorotatory
zwitterion
• The amino end is protonated and the
carboxylic end is deprotonated to form the
zwitterion, the dipolar form of an amino acid
AMINO ACIDS
AMINO ACIDS
AMINO ACIDS
PEPTIDE BOND
• Bond which connects 2 amino acid residues
• Possesses double bond character
• Connects the carboxyl group of one amino acid
to the amino end of the other amino acid
• Formed via a condensation reaction (formation
of a new bond upon the removal of water)
PEPTIDE BOND
PEPTIDE BOND
PEPTIDE BOND
PEPTIDE BOND
PEPTIDE CLASSIFICATION
•
•
•
•
2 A
...
A residues = tripeptide
12-20 A
...
A residues = polypeptide
Nomenclature of peptides
• All A
...
• Ex: alanyltyrosylaspartylglycine (AYDG)
• Ex2: phenylalanylglycine
Exercise #1
Draw the structure of the peptide formed when
you spell out your first name
Ex: SEAN
Proteins and polypeptides
• Proteins are composed of numerous
polypeptide chains
• Size, configuration may depend on the
protein’s function as well as location
proteins
AMINO ACID DERIVATIVES
• The 20 essential amino acids are not the only
AA which play a big role in many metabollic
pathways
• The Aas may undergo slight modifications via
different reactions to produce amino acid
derivatives
R GROUP MODIFICATION OF AMINO ACIDS
R GROUP MODIFICATION OF AMINO ACIDS
SPECTROSCOPIC PROPERTIES OF AMINO
ACIDS
• None of the AAs absorb light in the visible
region in the electromagnetic region
...
PROTEINS
3 major general classifications:
-globular
-fibrous
-membrane
PROTEIN STRUCTURE
PROTEIN STRUCTURE
PRIMARY STRUCTURE
• Amino acid sequence (peptide chains)
• Ex: AAAAAA, ALALALALA, GALA, CHEMISTRY
PRIMARY STRUCTURE
SECONDARY STRUCTURE
• Formed through intramolecular bonding such
as hydrogen bonding
...
• Usually present in globular form