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Announcements & Agenda (04/25/07) Will Pass Around Sign-In Sheet Indicate 2 times you can meet for review next week Choices: T @ 4, T @ 5, T @ 7 W @ 4, W @ 5, W @ 7 FINAL EXAM TIME: Thursday @ 10:30 am!!! Cumulative with 10-15 % New Stuff Exam 3 back Fri Complete HCTA: If >85 % Do Before Exam, You ALL get 2 extra credit points Today Protein Structure (16.5) Enzymes (16.6-16.8) Coenzymes (16.9) NO 3pm Review Today 1 CH 16 Practice Problems (MUST DO 10 OF THESE BY FRI) Will be counted as FINAL QUIZ! (EASY PTS) 16.01, 16.07, 16.11, 16.21, 16.25, 16.27, 16.29, 16.31, 16.33, 16.35, 16.37, 16.39, 16.41, 16.43, 16.49, 16.51, 16.55, 16.61, 16.63, 16.67, 16.69, 16.77, 16.81 Useful for Exam Prep on CH 16! 2 Last Time: Functions of Proteins Proteins perform many different functions in the body. KNOW THE CLASSES! Function of proteins determined by amino acids used and how they are put together in 2-D and 3-D 3 Last Time: Types of Amino Acids Nonpolar Polar 4 main kinds: • nonpolar (hydrophobic) with hydrocarbon side chains. • polar (hydrophilic) with polar or ionic side chains. • acidic (hydrophilic) with acidic side chains. • basic (hydrophilic) with –NH2 side chains. Acidic Basic Be able to recognize these 4 kinds, no need to memorize all 20 for the Final Exam!!!!!!!!!!!!!!!!! 4 Last Time: Formation of Proteins The Peptide Bond • The peptide bond is an amide bond. • forms between the carboxyl group of one amino acid and the amino group of the next amino acid. O + || H3N—CH2—C—O– + CH3 O | || + H3N—CH—C—O– O H CH3 O || | | || + H3N—CH2—C—N—CH—C—O– peptide bond 5 Tour of Protein Structure… 6 Last Time: Primary Structures • The nonapeptides oxytocin and vasopressin have similar primary structures. • Only the amino acids at positions 3 and 8 differ. 7 Primary Structure of Insulin Insulin • was the first protein to have its primary structure determined. • has a primary structure of two polypeptide chains linked by disulfide bonds. • has a chain A with 21 amino acids and a chain B with 30 amino acids. 8 Modification of insulin 9 Secondary Structure Elements • a 3-D arrangement of amino acids in a polypeptide chain. • result from intermolecular forces such as hydrogen bonding • Several types of secondary structure • • • • Alpha helices Beta sheets Triple helices Many more… 10 Secondary Structure – Alpha Helix • a 3-D spatial arrangement of amino acids in a polypeptide chain. • held by H bonds between the H of –N-H group and the O of C=O of the fourth amino acid down the chain. • a corkscrew shape that looks like a coiled “telephone cord”. 11 Beta Pleated Sheet • • • • polypeptide chains side by side. hydrogen bonds between chains. has R groups above and below the sheet. is typical of fibrous proteins such as silk, betakeratin, etc. 12 Secondary Structure – Triple Helix • three polypeptide chains woven together. • typical of collagen, connective tissue, skin, tendons, and cartilage. 13 Tertiary Structure • overall 3-D shape. • determined by attractions & repulsions between side chains of amino acids 14 Crosslinks in Tertiary Structures involve attractions and repulsions between the side chains of the amino acids in the polypeptide chain. 15 Example: Globular Proteins • have compact, spherical shapes. • carry out synthesis, transport, and metabolism in the cells. • such as myoglobin store and transport oxygen in muscle. Myoglobin 16 Quaternary Structure • combination of 2 or more protein units. • Example: hemoglobin consists of 4 subunits. • stabilized by the same interactions found in tertiary structures. Hemoglobin 17 Summary of Protein Structure 18 Denaturation • the disruption of bonds in the secondary, tertiary and quaternary protein structures. • heat and organic compounds: break apart H bonds and disrupt hydrophobic interactions. • acids and bases: break H bonds between polar R groups and disrupt ionic bonds. • heavy metal ions: react with S-S bonds to form solids (among many other things) • agitation such as whipping that stretches peptide chains until bonds break. 19 Applications of Denaturation • cooking. • the skin is wiped with alcohol. • heat is used to cauterize blood vessels. • instruments are sterilized in autoclaves. http://www.lifehouseproductions.com/remorgida.html 20 Enzymes: Biological Catalysts (16.6) • Catalyze nearly all chemical reactions taking place in the cells of the body. • Increase the rate of reaction by lowering the energy of activation. 21 Classification of Enzymes - classified by the reaction they catalyze. - names usually end in –ase & often identify reactant (substrate) and function of enzyme Class Oxidoreductases Transferases Hydrolases Lyases Isomerases Ligases Type of Reactions catalyzed Oxidation-reduction Transfer groups of atoms Hydrolysis Add atoms/remove atoms to or from a double bond Rearrange atoms Use ATP to combine small molecules 22 How They Work!!! In an enzyme-catalyzed reaction: • a substrate attaches to active site. • an enzyme-substrate (ES) complex forms. • Lock & key model (OLD, RIGID MODEL) • Induced-fit model (CURRENT MODEL) • reaction occurs, products released • an enzyme is used over and over. • Known functions of enzymes important in medical analyses E+S ES E+ P 23 Diagnostic Enzymes • often determine the amount of damage in tissues. • that are elevated may indicate damage or disease in a particular organ. 24 Diagnostic Enzymes Example Levels of enzymes CK, LDH, & AST • are elevated following a heart attack. • are used to determine the severity of the attack. 25 Factors Affecting Enzyme Activity! 26 Temperature Enzymes • are most active at an optimum temperature (usually 37°C in humans). • show little activity at low temperatures. • lose activity at high temperatures as denaturation occurs. 27 pH Enzymes • are most active at optimum pH. • contain R groups of amino acids with proper charges at optimum pH. • lose activity in low or high pH as tertiary structure is disrupted. 28 Optimum pH Values Most Enzymes in • the body have an optimum pH of about 7.4. • certain organs, enzymes operate at lower and higher optimum pH values. 29 Substrate Concentration As substrate concentration increases, • the rate of reaction increases (at constant enzyme concentration). • the enzyme eventually becomes saturated giving maximum activity. 30 Enzyme Inhibitors • are molecules that cause a loss of catalytic activity. • prevent substrates from fitting into the active sites. E+S E+I ES EI E+P no P Natural & Synthetic: Lots of drugs work by acting as inhibitors 31 Coenzymes (16.9) Coenzyme: a molecule which is ‘associated’ with the enzyme (but in not part of the amino acid sequence) that helps enzymes prepare the active site for catalytic activity. - many coenzymes derived from vitamins 32 Water-Soluble Vitamins • soluble in aqueous solutions. • cofactors for many enzymes. • not stored in the body. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 33 Fat-Soluble Vitamins • are A, D, E, and K. • are soluble in lipids, but not in aqueous solutions. • are important in vision, bone formation, antioxidants, and blood clotting. • are stored in the body. More on these on Friday! 34