By: Kim & Caitlin U NCOMMON AMINO ACIDS, AMINO ACIDS FORMING PROTEINS, & PRIMARY STRUCTURE OF A PROTEIN

UNCOMMON A MINO A CIDS  Derived from common amino acids  Produced by the parent amino acid being modified after protein is synthesized  Process is called post-translational modification

H YDROXYPROLINE & HYDROXYLYSINE  Both examples of uncommon amino acids  Unlike their parent amino acids, both have hydroxyl groups on their side chains  Found in some proteins in connective tissues  EX: Found in collagen

A MINO ACIDS FORMING PROTEINS  This reaction takes place in the cells by a mechanism  Producing an amide.  Any 2 amino acids can be linked together to form dipeptides  The two amino acids are joined together by a peptide bond Adding another would make it a tripeptide.  Every dipeptide still has a –COO and a –NH 3  Amino acids can be linked in different ways to form different dipeptides.  Some protein molecules contain more than 10,000 amino acid units

F ORMING P ROTEINS  Shorter chains are referred to as peptides while longer chains are referred to as polypeptides  Polypeptides contains a minimum of amino acids  Residues are a chain of amino acids  Abbreviations of 1-3 letters are usually used to represent proteins and peptides

S YNTHESIZING  C-terminus- amino acid at the end of a peptide that has a free α-carboxyl group  N-terminus- amino acid at the end of a peptide that has a free α-amino group  Proteins synthesize from the N-terminus to the C-terminus

P ROTEINS P ROPERTIES  Continuing patterns of peptide bonds form the backbone of peptides and proteins  Side chains- are called an R group  Up to 20 different side chains of the amino acid supply variety and also determine the chemical and physical properties of the protein  The most important property is acid-base behavior  Amino acids behave like zwitterions as do proteins

M ORE P ROPERTIES  In proteins repulsive forces between like charges on their surfaces determine water solubility  When a protein is at a pH where there is an equal number of positive and negative charges it is at its isoelectric point  When proteins are at their isoelectric point they are least soluble in water and can be precipitated from the solution

P RIMARY S TRUCTURE  In a primary structure of a protein the sequence of amino acids form a chain  Most peptides and protein molecules have different sequences of amino acids  Each sequence allows the protein to perform its function  Only a small fraction of all possible protein molecules have been made by biological organisms

P RIMARY S TRUCTURE  Like the naming of peptides the assignment of positions of the amino acids starts at the N-terminal end  There are 20 possibilities for the N-terminal amino acid  400 different dipeptides can be formed from 20 amino acids  The primary structure of a protein to a large extent, determines the native, or most frequently reoccurring secondary and tertiary structures

S EQUENCING  A change in sequence may or may not affect the function of a protein depending upon the change  An example of this is how bovine insulin is used for instant injections for humans. Even though the insulin is not identical in structure to human insulin it still performs the same task when introduced into a human. Although it does perform the same task it is not as effective.  An example of where a small change can have a huge effect is in the protein of the blood, hemoglobin. A change in one amino acid can cause the disease sickle cell anemia