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14.5 Uncommon Amino Acids Uncommon amino acids • Some but not all occur in protein • Come form common amino acids that are synthesized by the organism; process called post-translation modification • Hydroxyproline and hydroxylysine differ form their parent amino acid because an –OH group Cont. • Thyroxine is different from tyrosine because it has an extra iodine • “is found only in the Thyroid Gland” • Thyroxine is a hormone that is released by proteolysis • Some common, uncommon amino acids are: Proline, hydroxyproline, Lysine, hydroxylysine, Tyrosine, Thyroxine 14.6 Amino acids combining to form Proteins 14.6 • Two amino acids are joined together by a peptide bond. (also called a peptide linkage) • Any two amino acids can be linked together. (this forms dipeptides) • A third amino acid would be called a tripeptide. • Proteins are an important part of a living organism 14.6 • Short chains are called peptides • Longer chains are called polypeptides • Amino acids in a chain are called residues. 14.7 What are the Properties of Proteins? • A continuing pattern of peptide bonds forms the backbone of the protein • The R groups are called the side chains • Acid-base behavior is one of the most important behaviors of the 20 different side chains • They behave as Zwitterions 14.7 charges of Proteins • Isoelectric point of a protein occurs at the pH where there's a balance in positive and negative charges • any pH above the isoelectric point is negative • Any below is positive • Some proteins like hemoglobin have an equal charge 14.7 Solubility • The solubility of proteins depends on the repulsive forces in the surface • When there is no repulsive forces the molecules clump up and the solubility is reduced • They are least soluble at there isoelectric points 14.8 What is the Primary structure of Proteins? 14.8 structures of proteins • Amino acids are the primary structures that make up a chain of protein • Different sequences of peptide and protein molecules allows for the protein to carry out its functions • The formula for calculating the possible numbers of peptides and proteins for a chain of n amino acids by raising it to the 20th power • 20ⁿ 14.8 cont. • Peptides and proteins have their own unique sequence of amino acids in the body • Human insulin has two chains with a total of 51 amino acids. • The two chains are connected by disulfide bonds. • People with diabetes have to take insulin shots. • Insulin used is from cattle and sheep. 14.8 cont. • One change in the amino acid sequence can cause sickle cell anemia. • This shows how important the sequence of the amino acid sequence is.