Enzymatic Reactions: Enzymes, Metabolism & Redox Reactions - PDF

Introduction to Enzymatic Reactions 1  Enzymes 2 Specialized proteins designed to catalyze reactions while they are unchanged by the reaction  Lower the activation energy for a chemical reaction  Often facilitate...

Introduction to Enzymatic Reactions 1  Enzymes 2 Specialized proteins designed to catalyze reactions while they are unchanged by the reaction  Lower the activation energy for a chemical reaction  Often facilitate breakdown of one substrate to build another  Enzymes control all metabolic pathways and facilitate the effects of the majority of hormones Fig. 2.2. Kenney et al. 2015. Physiology of Sports… Human Kinetics  Lock & Key Model 3 Enzyme‐substrate interaction  Ensures that the correct enzyme matches with its specific substrate to perform a particular function  Only the required substrates will fit in that specific enzyme  Changing the shape of the enzyme impacts its function Fig. 5.8. McArdle et al. 2010. Exercise Physiology… LWW 3  Enzyme Terminology 4 Almost all enzyme names end in –ase Kinase or Phosphorylase (Transferases) Transfers a phosphate group Oxidoreductases Eg. Dehydrogenase or Oxidase Catalyze redox rxns Transfers hydrogen atoms Isomerase Rearranges molecular structures Synthase Fig. 9.6. Freeman. 2011. Biological Science. Pearson  Kinase Example 5 Hexokinase removes a phosphate group from ATP and adds it to glucose.  This is the first step of glycolysis and traps glucose in a muscle cell Glucose‐6‐phosphate (G6P) Glucose  Dehydrogenase Example 6 Lactate dehydrogenase removes 2 hydrogens (and electrons) from lactate and adds them to NAD+  Isomerase Example 7 Glucose and fructose are isomers meaning that they both have the same chemical formula (C6H12O6), but glucose is a hexagon shape, while fructose is a pentagon shape  Glucose isomerase simply changes the shape without changing the formula Synthase Example 8 ATP synthase is used to synthesize ATP by simply adding a phosphate (PO3‐) to ADP. Thisis the final step of the electron transport chain (ETC) in the mitochondria. We get over 90% of our ATP from this enzymatic reaction!!! ATP Synthase Inorganic Phosphtate (Pi) ADP ATP Coenzymes 9 Coenzymes Nonprotein organic substances that facilitate enzyme action by binding a substrate to its specific enzyme (e.g. NAD, FAD) Often changed by the rxn Mass Action Effect 10 Mass action effect  Substrate availability affects metabolic rate  More available substrate = higher pathway activity  Excess of given substrate = cells rely on that energy substrate more than others  Rate‐Limiting Enzymes 11 A rate‐limiting enzyme controls the speed of a metabolic process Exercise intensity / speed directly reflects the body’s capacity to transfer chemical energy to mechanical work  Temperature, pH, and other chemicals can alter enzyme activity Fig. 2.3. Kenney et al. 2019. Physiology of Sports… Human Kinetics  Hydrolysis & Condensation 12 Hydrolysis chemical bonds by adding H+  Splits and OH‐ to the reaction byproducts  Catabolizes macronutrients into simpler forms that the body easily absorbs and assimilates  Requires an H2O Condensation  Structural components of the nutrients bind together to form more complex molecules and compounds  “Releases” an H2O  Redox Reactions 13 OIL RIG Oxidation  Reactions that transfer (lose) electrons (or hydrogen atoms) Reduction  Anyprocess in which atoms in an element gain electrons (or H+) Redox Reactions: LDH Rxn 14 The lactate dehydrogenase (LDH) reaction in recovery is an excellent example of a redox reaction. OIL RIG In recovery from exercise, lactate is oxidized (loses 2 H+) to become pyruvate.  NAD+ gains one H (and 2 electrons) and is reduced to become NADH, while an extra H+ is nearby  Fig. 3.5. Powers & Howley. 2012. Respiratory Chain and Exercise Physiology… McGraw-Hill Electron Transport 15 The vast majority (~90%) of our ATP comes from these redox reactions. Electron transport: Represents the final common pathway in aerobic metabolism  For each pair of hydrogen atoms, two electrons flow down the chain and reduce one oxygen atom  Process ends when oxygen accepts two hydrogens and forms water Review Questions 16 Understand the purpose of a rate‐limiting enzyme and be able to identify the rate‐limiting enzyme in the main energy systems (phosphagen, glycolytic, and oxidative). Identify the function of specific enzymes based on their names. Identify condensation and hydrolysis reactions. Identify which substrates are being reduced and which are being oxidized in specific redox reactions. Ex. The LDH reaction in recovery from exercise. Figure & Notes References 17 Kenney, Wilmore, Costill. Physiology of Sport and Exercise (5th ed). Human Kinetics, 2011. McCardle, Katch, Katch. Exercise Physiology: Nutrition, Energy, and Human Performance, 8th Edition. Wolters Kluwer Health, 2015. Powers & Howley. Exercise Physiology: Theory & Application to Fitness and Performance, 8th Edition. McGraw‐Hill, 2011. Fig. 9.6. Freeman. 2011. Biological Science. Pearson Coenzymes: iron, zinc, B vitamins (niacin, riboflavin, thiamin) Glucose and fructose are isomers. Both have the chemical formula C6H12O6, but different 3D structures Synthase enzymes synthesize specific molecules Hydrolysis enzyme examples: ATPase, lactase, sucrase OIL RIG Oxidation Involves Loss Reduction Involves Gain Note that these are always coupled reactions. If something is being oxidized, then something else also has to be reduced. Traditional chemistry defines redox reactions by the gaining or losing of electrons. However, the majority of redox reactions that we will discuss in this class are dehydrogenase reactions and involve the moving of hydrogens. So I often try to simplify this topic by following the movement of those hydrogens when deciding whether something is being oxidized or reduced. OIL RIG: Oxidation Involves Loss & Reduction Involves Gain Note that these are always coupled reactions. If something is being oxidized, then something else also has to be reduced. Traditional chemistry defines redox reactions by the gaining or losing of electrons. However, the majority of redox reactions that we will discuss in this class are dehydrogenase reactions and involve the moving of hydrogens. So I often try to simplify this topic by following the movement of those hydrogens when deciding whether something is being oxidized or reduced. Lactate dehydrogenase example (during recovery from exercise) Lactate + NAD+  Pyruvate + NADH + H+ LDH also works in reverse during high intensity exercise. Pyruvate + NADH + H+  Lactate + NAD+