Section 14.5 – What Are Uncommon Amino Acids?

Uncommon Amino Acids Derived from the common amino acids Produced by modification of the parent amino acid

Uncommon Amino Acids Hydroxyproline and hydroxylysine differ from parent amino acids in that they have hydroxyl groups on their side chain. Found in connective tissue protein such as collagen.

Uncommon Amino Acids Thyroxine has an extra iodine-containing aromatic group on its side chain. Found only in the thyroid gland. Formed by post-translational modification of tyrosine residues in the protein thyroglobulin.

14.6 – How Do Amino Acids Combine to Form Proteins? The -COO¯ group of an amino acid molecule can be combined with the –NH3+ group of a second molecule

Peptide Bond Joins the two amino acids together – product is dipeptide The order of amino acid in a peptide or protein is critical to both the structure and function. Any two amino acids, whether the same or different, can be linked together to form dipeptides. Contain a –COO and an –NH3 group so a third amino acid can be added – product is a tripeptide. Process continues creating a tetrapeptide, pentapeptide, and so on. These long chain amino acids are the proteins in living organisms

Peptides Short Chain – Peptides Longer Chains – Polypeptides Even Longer Chains – Proteins Amino acids in a chain are called residues

14.7 Properties of Proteins Repeating patterns of peptides are what forms the protein chain. The R groups in the chain are called side chains. The 20 different amino acid side chains supply variety and determine the physical and chemical properties of proteins. Proteins are least soluble in water at their isoelectric points and can be precipitated from their solutions

14.8 Primary Structure of Proteins Consists of the sequence of amino acids that make up the chain. Each molecule in living organisms has a different sequence of amino acids allowing it to carry out its specific function. 400 different dipeptides possible 8000 tripeptides possible The primary structure of a protein determines the most frequently occuring secondary and tertiary structures. The change in an amino acid sequence may or may not change the function of the protein