PROTEINS
Proteins (Greek proteios, ―primary or ―of first importance) are biochemical molecules
consisting of polypeptides joined by peptide bonds between the amino and carboxyl groups
of amino acid residues.
Proteins perform a number of vital functions:
Enzymes are proteins that act as biochemical catalysts.
Many proteins have structural or mechanical functions (e.g., actin and myosin in
muscles).
Proteins are important in cell signaling, immune responses, cell adhesion, and the cell
cycle.
Proteins are a necessary component in animal diets.
Amino Acids
All proteins are polymers containing chains of amino acids chemically bound by amide
(peptide) bonds.
Most organisms use 20 naturally-occurring amino acids to build proteins.
The linear sequence of the amino acids in a protein is dictated by the sequence of the
nucleotides in an organisms’ genetic code.
These amino acids are called alpha (α)-amino acids because they have a carboxyl group
and an amino group bonded to the same carbon atom, the α- carbon. They differ from
each other in their side chains, or R groups, which vary in structure, size, and electric
charge, and which influence the solubility of the amino acids in water.
In addition to these 20 amino acids there are many less common ones. Some are residues
modified after a protein has been synthesized others are amino acids present in living
organisms but not as constituents of proteins.
1
,The amino acids are classified by R group side chains, into five classes based on the
properties of their R groups, in particular, their polarity, or tendency to interact with
water at biological pH (near pH 7.0).
The polarity of the R groups varies widely, from nonpolar and hydrophobic (water-
insoluble) to highly polar and hydrophilic (water-soluble) and the charge
Non polar aliphatic R groups
Polar uncharged R group
Aromatic R group
Positively Charged R-Groups
Negatively Charged R Groups
The natural Amino Acids
2
, 3
Proteins (Greek proteios, ―primary or ―of first importance) are biochemical molecules
consisting of polypeptides joined by peptide bonds between the amino and carboxyl groups
of amino acid residues.
Proteins perform a number of vital functions:
Enzymes are proteins that act as biochemical catalysts.
Many proteins have structural or mechanical functions (e.g., actin and myosin in
muscles).
Proteins are important in cell signaling, immune responses, cell adhesion, and the cell
cycle.
Proteins are a necessary component in animal diets.
Amino Acids
All proteins are polymers containing chains of amino acids chemically bound by amide
(peptide) bonds.
Most organisms use 20 naturally-occurring amino acids to build proteins.
The linear sequence of the amino acids in a protein is dictated by the sequence of the
nucleotides in an organisms’ genetic code.
These amino acids are called alpha (α)-amino acids because they have a carboxyl group
and an amino group bonded to the same carbon atom, the α- carbon. They differ from
each other in their side chains, or R groups, which vary in structure, size, and electric
charge, and which influence the solubility of the amino acids in water.
In addition to these 20 amino acids there are many less common ones. Some are residues
modified after a protein has been synthesized others are amino acids present in living
organisms but not as constituents of proteins.
1
,The amino acids are classified by R group side chains, into five classes based on the
properties of their R groups, in particular, their polarity, or tendency to interact with
water at biological pH (near pH 7.0).
The polarity of the R groups varies widely, from nonpolar and hydrophobic (water-
insoluble) to highly polar and hydrophilic (water-soluble) and the charge
Non polar aliphatic R groups
Polar uncharged R group
Aromatic R group
Positively Charged R-Groups
Negatively Charged R Groups
The natural Amino Acids
2
, 3
