Amino acids – the monomers There are 20 different amino acids found in proteins. Each has a different “R” group (side chain).
The twenty amino acids found in living organisms, organized according to characteristics of R-groups. Such properties contribute to proteins folding into various shapes
Amino acids (monomers) are linked to form polypeptide chains (polymers) by dehydration synthesis (condensation reax) Additional amino acids can be added by condensation reaction. The covalent bond that forms between amino acids is called a peptide bond. Polypeptide chains have an N terminus and a C terminus, where peptide bond forms between amino acids.
Fibrous Proteins Include those which function as structural proteins and which play a role in motility and contraction typically water-insoluble built up from single repeating elements of secondary structure rope-like proteins that provide strength and framework to tissues
Fibrous Protein Example 1: Collagen most abundant protein in vertebrates (~ 20 % of all proteins in human body) found in cartilage, tendons, bones, teeth, skin, and blood vessels extremely strong
Fibrous Protein Example 2: α-Keratin soft or hard fibrous protein highly insoluble in water composed of multiple α-helices twisted into thicker filaments
Globular Proteins Include most transport proteins, enzymes, and hormones typically water-soluble, roughly spherical and tightly folded hydrophilic nature – polar residues = on the surface – hydrophobic residues = on the interior many diverse structures are possible
Globular Protein Example 1: Hemoglobin each subunit of hemoglobin is a globular protein with an embedded heme group. In adult humans, the most common hemoglobin protein is a tetramer consisting of four polypeptide chains The heme group consists of an iron atom held in a ring, This iron atom is the site of oxygen binding.
Globular Protein Example 2: Enzyme Pepsin a protease (protein- digesting enzyme), which is active in the stomach consists of 327 amino acid residues has a deep cleft, the bottom of which contains a pair of aspartate residues on either side of the cleft which break peptide bonds in proteins by the addition of water: -H to one side and -OH to the other.