Chapter Twenty One Enzymes and Vitamins. Ch 21 | # 2 of 47 Catalysts for biological reactions Proteins Lower the activation energy Increase the rate of.

Presentation on theme: "Chapter Twenty One Enzymes and Vitamins. Ch 21 | # 2 of 47 Catalysts for biological reactions Proteins Lower the activation energy Increase the rate of."— Presentation transcript:

1 Chapter Twenty One Enzymes and Vitamins

2 Ch 21 | # 2 of 47 Catalysts for biological reactions Proteins Lower the activation energy Increase the rate of reaction Have specific shapes that match the shapes of reactants Activity lost if denatured May be simple proteins or complex May contain cofactors such as metal ions or organic (vitamins) Enzymes

3 Ch 21 | # 3 of 47 End in –ase Identifies a reacting substance sucrase – reacts sucrose lipase - reacts lipid Describes function of enzyme oxidase – catalyzes oxidation hydrolase – catalyzes hydrolysis Common names of digestion enzymes still end –in pepsin, trypsin Names of Enzymes

4 Ch 21 | # 4 of 47 Class Reactions catalyzed Oxidoreductoases oxidation-reduction Transferases transfer group of atoms Hydrolases hydrolysis Lyases add/remove atoms to/from a double bond Isomerases rearrange atoms Ligases combine molecules using ATP Classification of Enzymes

5 Ch 21 | # 5 of 47 Oxidoreductoases oxidases - oxidize reductases – reduce Transferases transaminases – transfer amino groups kinases – transfer phosphate groups Hydrolases proteases - hydrolyze peptide bonds lipases – hydrolyze lipid ester bonds Lyases carboxylases – add CO 2 hydrolases – add H 2 O Examples of Enzyme Classification

6 Ch 21 | # 6 of 47 Enzyme Structure The shape/structure of enzymes is related to their functions –Simple enzymes Enzymes that consist only of protein –Conjugated enzymes Enzymes that consist of protein and a nonprotein part Apoenzyme + cofactor = holoenzyme Coenzyme: small organic molecule that serves as a cofactor in a conjugated enzyme (needed to prepare the active site for catalytic activity)

7 Ch 21 | # 7 of 47 Vitamins Organic compounds that are essential for the proper functioning of the human body –Many function as cofactors Cannot be synthesized by the human body Must be obtained from dietary sources Two main classes: –Water-soluble –Fat soluble

8 Ch 21 | # 8 of 47 Water-Soluble Vitamins Soluble in aqueous solutions Used as cofactors by many enzymes Not store in the body Vitamin C Vitamin B

9 Ch 21 | # 9 of 47 Fat-Soluble Vitamins Vitamins A, D, E, and K Soluble in lipids, but not in aqueous solutions Important in vision, bone formation, antioxidants, and blood clotting Stored in the body

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14 Ch 21 | # 14 of 47 An enzyme binds a substrate in a region called the active site –Only certain substrates can fit the active site –Amino acid R groups in the active site help substrate bind and align correctly Enzyme-substrate complex forms Substrate reacts to form product Product is released Enzyme Action

15 Ch 21 | # 15 of 47 The active site of an enzyme can be a crevice-like region formed as a result of the protein’s secondary and tertiary structural characteristics.

16 Ch 21 | # 16 of 47 Enzyme Specificity Enzymes may recognize and catalyze: –1. A single substrate: Absolute Specificity Example: Urease (only catalyzes the hydrolysis of urea) –2. A single stereoisomer: Stereochemical Specificity Example: L-amino-acid oxidase (catalyzes the oxidation of L-amino acids, but not D-amino acids)

17 Ch 21 | # 17 of 47 Enzyme Action: Lock and Key Model In the lock and key model of enzyme action: –The active site has a rigid shape –Only substrates with the matching shape can fit –The substrate is a key that fits the lock of the active site

18 Ch 21 | # 18 of 47 Enzyme Action: Lock and Key Model

19 Ch 21 | # 19 of 47 + + E + S ES complex E + P S P P S Lock and Key Model

20 Ch 21 | # 20 of 47 Enzyme Specificity Enzymes may recognize and catalyze: –3. A group of similar substrates: Group Specificity Example: Hexokinase (adds a phosphate to hexoses) –4. A particular type of bond: Linkage Specificity Example: Chymotrypsin (catalyzes the hydrolysis of peptide bonds)

21 Ch 21 | # 21 of 47 Enzyme structure flexible, not rigid Enzyme and active site adjust shape to bind substrate Increases range of substrate specificity Shape changes also improve catalysis during reaction Enzyme Action: Induced Fit Model

22 Ch 21 | # 22 of 47 Enzyme Action

23 Ch 21 | # 23 of 47 E + S ES complex E + P S P P SS Enzyme Action: Induced Fit Model

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25 Ch 21 | # 25 of 47 Enzyme Activity

26 Ch 21 | # 26 of 47 Little activity at low temperature Rate increases with temperature Most active at optimum temperatures (usually 37°C in humans) Activity lost with denaturation at high temperatures Factors Affecting Enzyme Action: Temperature

27 Ch 21 | # 27 of 47 Maximum activity at optimum pH Narrow range of activity Most lose activity in low or high pH Why is one pH better than another? –R groups of amino acids have proper charge at certain pH values –Tertiary structure of enzyme is correct Factors Affecting Enzyme Activity: pH

28 Ch 21 | # 28 of 47 Increasing substrate concentration increases the rate of reaction (enzyme concentration is constant) Maximum activity reached when all of enzyme combines with substrate Factors Affecting Enzyme Activity: Substrate Concentration

29 Ch 21 | # 29 of 47 Factors Affecting Enzyme Activity: Enzyme Concentration The rate of reaction increases as enzyme concentration increases (at constant substrate concentration) At higher enzyme concentrations, more substrate binds with enzyme

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31 Ch 21 | # 31 of 47 Inhibitors Molecules that cause a loss of catalytic activity Change the protein structure of an enzyme to prevent substrates from fitting into the active sites May be “competitive” or “noncompetitive” Some effects are irreversible Enzyme Inhibition

32 Ch 21 | # 32 of 47 A competitive inhibitor Has a structure similar to substrate Occupies active site Competes with substrate for active site Has effect reversed by increasing substrate concentration Competitive Inhibition https://www.eccentrix.com/members/chempics/Slike/Enzyme/2Competitive_inhibition.jpg

33 Ch 21 | # 33 of 47 A noncompetitive inhibitor Does not have a structure like substrate Binds to the enzyme but not active site Changes the shape of enzyme and active site Substrate cannot fit altered active site No reaction occurs Effect is not reversed by adding substrate Substrate activity is restored when inhibitor is no longer bonded to the enzyme Noncompetitive Inhibition

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36 Ch 21 | # 36 of 47 Heavy metal poisoning is an example of noncompetitive inhibition of an enzyme.

37 Ch 21 | # 37 of 47 Irreversible Inhibition In irreversible inhibition, a substance destroys enzyme activity by bonding with R groups at the active site Inhibitor permanently blocks substrate binding –One of the ways antibiotics kill bacteria

38 Ch 21 | # 38 of 47 Structures of selected sulfa drugs in use today as antibiotics. Sulfa Drugs

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40 Ch 21 | # 40 of 47 Regulating Enzyme Activity Four main mechanisms to regulate enzyme activities –Genetic Control –Feedback Control –Zymogen Activation –Allosteric Regulation Activation – Positive Regulation Deactivation – Negative Regulation

41 Ch 21 | # 41 of 47 Feedback Control In feedback control: –A product of a reaction acts as a negative regulator –An end product binds with the first enzyme in a sequence when sufficient product is present E1 E2 E3 A  B  C  D Inhibition of enzyme 1 by product D

42 Ch 21 | # 42 of 47 Zymogens –Inactive forms of enzymes –Activated when one or more peptides are removed –Example: Proinsulin is converted to insulin by removing a small peptide chain –Digestive enzymes are produced in one organ as zymogens, but not activated until they are needed; Ex. trypsinogen / trypsin

43 Ch 21 | # 43 of 47 Allosteric Enzymes An enzyme with two or more protein chains (quaternary structure) and two kinds of binding sites (substrate and regulator) –Activity is influenced by “regulators” (found or produced in cells normally) Positive regulator –Enhances the binding of substrate and accelerates the rate of reaction Negative regulator –Prevents the binding of the substrate to the active site and slows down the rate of reaction

44 Ch 21 | # 44 of 47 Enzymes and Vitamins Levels of enzymes in blood used as a diagnostic tool.

45 Ch 21 | # 45 of 47 Diagnostic Enzymes The levels of diagnostic enzymes determine the amount of damage in tissues

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