Protein and Amino Acid Classification Lecture 1 PDF

Proteins and Amino Acids Assoc. Prof. Hesham Haffez Structural Differences Between Carbohydrates, Lipids, and Proteins  Proteins They are nitrogenous macromolecules with high molecular weight formed of carbon, oxygen, hydrogen and nitroge...

Proteins and Amino Acids Assoc. Prof. Hesham Haffez Structural Differences Between Carbohydrates, Lipids, and Proteins  Proteins They are nitrogenous macromolecules with high molecular weight formed of carbon, oxygen, hydrogen and nitrogen. Proteins may also contain sulfur, phosphorus and metal ions. They are polymers formed of subunits called amino acids linked together by peptide linkage. Provide structure, catalyze cellular reactions and other tasks. Have multiple biological functions Classified according to their biological roles. Structure of Proteins Made up of chains of amino acids; classified by number of amino acids in a chain Peptides: fewer than 50 amino acids Dipeptides: 2 amino acids Tripeptides: 3 amino acids Polypeptides: more than 10 amino acids Proteins: more than 50 amino acids Typically, 100 to 10,000 amino acids linked together Types of proteins and their function Enzymes Most varied and specialized proteins with catalytic activity. All chemical reactions of organic biomolecules in cells are catalyzed by enzymes. Types of proteins and their function Transport Proteins Bind and carry molecules or ions to organs in the blood plasma. Lipoproteins in blood plasma carries lipids from the live to other organs. Types of proteins and their function Nutrient and Storage Proteins Seeds of many plants store nutrient proteins required for the growth of the germinating seedlings. Albumin, the major protein of egg white, and casein the major protein of milk are examples of nutrient proteins. Types of proteins and their function Contractile or Motile Proteins Some proteins in organisms have the ability to contract, to change shape, or to move about. Tubulin is the protein from which microtubules are built. Types of proteins and their function Structural Proteins Many proteins serve as supporting filaments, cables, or sheets, to give biological structures strength or protection. Major component of tendons and cartilage is the fibrous protein collagen, which has very high tensile strength. Ligaments contain elastin, a structural protein. Types of proteins and their function Defense Proteins Defend organisms against invasion by other species or protect them Immunoglobulin or antibodies, are made by the lymphocytes of vertebrates and can recognize & precipitate or neutralize invading bacteria Fibrinogen and thrombin are blood clotting proteins Types of proteins and their function Regulatory Proteins Help regulate cellular or physiological activity. The cellular response to many hormonal signals is often mediated by a class of GTP-binding proteins called G proteins. Amino Acids: Building Blocks of Proteins Every amino acid has the same fundamental structure which consists of a central carbon bonded to an amino group, a carboxyl group & a hydrogen atom. The Anatomy of an Amino Acid Peptide Bonds Link Amino Acids Form when the acid group (COOH) of one amino acid joins with the amine group (NH2) of a second amino acid Formed through condensation Broken through hydrolysis Condensation and Hydrolytic Reactions Amino Acids: Side Groups There are 20 different types of amino acids used in making proteins. The essential structure is the same in all 20 molecules. The 20 molecules differ in the side groups.  General properties of amino acids Standard or Proteinogenic amino acids They are twenty α-amino acids that are utilized in living cells for protein synthesis during the translation process. Non-proteinogenic They exist either in the free form or bound up into larger molecules (as constituents of peptides and proteins and other types of amide, and of alkylated and esterified structures). Non-proteinogenic amino acids exist mainly in bacteria, fungi and algae and other plants.  General properties of amino acids They all, except glycine, have a chiral nature, influencing the reactions that the compound will undergo.  General properties of amino acids Readily solvated by water, it is soluble in polar solvents and insoluble in non-polar (organic) solvents such as benzene. It has high melting point; it needs high energy to disrupt the ionic bonds stabilizes its lattice. Alcohol precipitates the amino acids from its solution. Only L-amino acids occur in proteins and in mammalian metabolism, However, D-amino acids do occur in bacterial cell walls (murein).  Functions of amino acids 1.Component of peptides, proteins and phospholipids. 2. Precursors of keto acids, biogenic amines, glucose, nucleotides, heme and creatine. 3. Neurotransmitters e.g. glutamate, aspartate and glycine 4. Transport molecule for NH2 group (Glutamine) Amphoteric Nature of amino acid and Isoelectric pH O O O + + H3N CH C OH H3N CH C O- H2N CH C O- R R R Cation Zwitterion Anion (isoelectric pH)  Zwitter ion formation “Amino acids are positive and negative” - The presence of both an acid and a base (amine) in the same molecule leads to an interaction between the two. The carboxy group will donate a proton to the amino group, so that an amino acid (in the absence of other acids or bases) will carry both a negative and a positive charge, making the whole molecule appear uncharged. - NB: The unionized amino acid molecule does not actually exist!!  The isoelectric point  The isoelectric point (pI) is the pH at which the number of positive charges on the molecule is the same as the number of negative charges.  At the pI the molecule would therefore appear uncharged. At this pH, the molecules ability to interact with water is lowest, and therefore its solubility is low. At a pH below the pI, some of the ammonium groups will be protonated so amino acid is soluble. At a pH above the pI, some of the carboxylate groups will be deprotonated so amino acid is soluble. At a pH equal the pI, number of positive and negative charge are equal and so amino acid/protein is precipitated.