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Proteins Proteins makeup 50% -60% of your dry weight Composed of C H O N (and sometimes S and P) They are very large molecules ex. β- lactoglobulin – C1642H2652O550N420S18 Insulin – C254H227O75N65S6 Functions of Proteins 1. 2. 3. 4. 5. 6. 7. 8. enzymes oxygen transport (haemoglobin) blood clotting (fibrin) immunological defense (antibodies) food reserves (albumin, casein in milk) hormones structural (hair, nails, skin) muscular movement (actin/myosin) Composition of Proteins Proteins are composed of amino acids = monomer General structure note A central C An H group An amino group A carboxyl group A variable ‘R’ group For each AA there is a different ‘R’ group which lends that AA certain chemical properties ex. Glycine – R = H Alanine – R = CH3 Serine – R= CH2OH In solution, the carboxyl group acts as a weak acid, and the amino group acts as a weak base. Thus, amino acids can exist in three different ionic states depending on the pH. (varied properties) There are 20 common types of AA’s can be grouped by properties of side chains: 1. nonpolar side groups (hydrophobic) – less soluble in water 2. polar side groups (hydrophilic) –soluble in water; grouped further into: a. charged b. uncharged There are 8 essential AA’s in human adults (9 in children) and the body must get these in the diet the others can be synthesized Protein Structure Polypeptide chains = polymers of amino acids, linked by peptide bonds, arranged in a specific linear sequence. Peptide bond = covalent bond formed by condensation reaction that links carboxyl group of one amino acid to amino group of another. Peptides = are folded and coiled into 3D conformational structures Polypeptide chains range in length and have unique linear sequences. 3D Conformation = Protein Function A protein’s 3D structure: enables a protein to recognize and bind specifically to another molecule is a consequence of the specific linear sequence of amino acids in the polypeptide is produced as a result of the folding and coiling of peptide is stabilized by chemical bonds and weak interactions between neighboring regions of folded protein The properties of R-groups influence the folding and coiling of peptide. Primary (1o) Structure Unique sequence of AA in protein Determined by genes Slight change can affect protein’s conformation and function (e.g. Sickle Cell Anemia –only 1 AA is substituted) Secondary (2o) Structure Chemical interactions between AA’s determine configuration of molecule in 3D space H-H bonds along the backbone of the protein Types of 2o structure: i) α helix hair, wool ii) sheets silk, spider webs iii) “seemingly” random coils Tertiary (3o) Structure further chemical interactions between R-groups of certain AA’s lend further 3D shape: 1) weak interactions stabilize protein: i. hydrophobic interactions between nonpolar Rgroups ii. hydrogen bonding between polar side chains iii. ionic bonds between charged side chains 2) covalent linkages: i. S-S bridges form between 2 cysteine AA’s these ‘hold’ the 3D structure together Very Important Quaternary (4o) Structure Interactions between polypeptide chains to form larger protein molecules Not all proteins undergo 4o structure ex. Haemoglobin Collagen (triple helix) Protein Function ‘Shape determines function’ a proteins function id determined by it’s configuration denaturation (destruction of shape) will result in a loss of function denatured proteins will halt the biochemical pathways they catalyze Factors which will Denature Proteins pH change salt concentration various chemicals (organic solvents) temp change digestive system (ex. gastrin) Enzymes Enzymes are biological catalysts The rates of reaction depends on: concentration of enzymes concentration of substrate presence of coenzymes/cofactors/inhibitors temperature pH