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Proteins! Proteins Proteins account for more than 50% of the dry mass of most cells Monomer: amino acids 20 amino acids used in cells Central carbon atom One hydrogen attached Amine (NH2) and carboxylic acid (COOH) groups attached to carbon Only thing different is side chain…R-group (side chain) Responsible for 3D shape of protein Polymer: polypeptide chains (proteins) Link between monomers is called: polypeptide bond or PEPTIDE bond Made by a dehydration reaction (between amine group of one aa and carboxyl group of another aa) Functions of Proteins Structural support/strengthening Catalysts (enzymes) Storage Transport Cellular communications Movement Defense against foreign substances Some famous proteins… Essential components of cell membranes Oxygen-carrying pigment hemoglobin (haemoglobin) Antibodies which attack and destroy invading microorganisms Enzymes! Collagen! (fibrous) Amino Acids 20 -23 major AA (others have been synthesized in labs) STRUCTURE Amino group on one end (-NH2) Carboxylic acid group on one end (COOH) Hydrogen R-group/side chain (changes) Alanine Glycine Peptide Bond When two amino acids (AA#1 and AA #2) join,… AA #1 loses a hydroxyl group (-OH) from its carboxylic acid (-COOH) side AA #2 loses a hydrogen from its amine (NH2) group The Carbon atom in the carboxyl group of AA#1 is now free to make ONE bond with the Nitrogen of the amine group in AA#2 This bond is called a PEPTIDE Bond H- and –OH removed…what is this??? WATER!!! Another condensation reaction (dehydration) Dipeptide Molecule New molecule formed by joining 2 amino acids Polypeptide Molecule Molecule made up of many amino acids joined by peptide bonds Polypeptide is the POLYMER (not protein) Complete protein may contain one polypeptide chain, twisted and folded or two or more polypeptide chains interacting with each other Polypeptide bonds Where are amino acids linked? In living cell Ribosomes! These reactions that occur on the ribosomes are controlled by ENZYMES (more on this later) How are polypeptides broken? Hydrolysis Reactions Naturally occurs in stomach and small intestine Protein in food is hydrolyzed into amino acids prior to being absorbed by the blood Once in the blood, these AA can be restructured into polypeptides and then twisted and folded into functioning PROTEINS the cells in you body needs Protein Structure Primary structure 1’ Order of amino acids in a polypeptide chain Secondary structure 2’ Polypeptide chain folds because of interactions between amino acids HYDROGEN BONDING Tertiary Structure 3’ Gives proteins 3-D shape VERY IMPORTANT to function of protein Beta pleated sheets and alpha helices fold based on interactions between R-groups of a.a. Hydrogen bonds, polar/non-polar interactions, acid/base interactions, disulfide bonds, van derWaals forces Quaternary Structure 4’ the association of the polypeptide chains some proteins contain more than one polypeptide chain Each polypeptide chain in the protein is called a subunit Two or more subunits come together for a specific function HEMOGLOBIN On Red blood cells Its shape allows RBCs to carry oxygen all around your body! 1. Practice Set 4 (6 MC and 1 SAQ) 2. 3. 4. 5. 6. 7.