1. Functional Human Physiology for the Exercise and Sport Sciences Cell Metabolism Jennifer L. Doherty, MS, ATC Department of Health, Physical Education, and Recreation Florida International University

2. Metabolism All body activities depend on the availability of chemical energy.  Chemical energy provided by Adenosine Triphosphate (ATP)  Regulated and controlled by enzymes Metabolism  All the chemical reactions that take place within body cells.  Metabolic chemical reactions include: 1)Reactant  Substance that enters a chemical reaction. 2)Product  Substance produced as a result of a chemical reaction.

3. Types of Metabolic Reactions Anabolism or Synthesis  Chemical bonds are made.  Small molecules, ions, or atoms are joined to form larger molecules. 1)A + B → AB  Energy is required or consumed. Catabolism or Decomposition  Chemical bonds are broken.  Large molecules are broken down into small molecules, ions, or atoms. 1)AB → A + B  Energy is released, produced, or provided.

4. Hydrolysis and Condensation Reactions Hydrolysis  Adding water to break apart molecules into fragments.  Example 1)Adding water to glycogen to split into its glucose component parts. Condensation  Removal of water to join molecules together  Examples 1)Joining molecules of glucose together to form glycogen. 2)Joining amino acids together to form dipeptides.

5. Phosphorylation and Dephosphorylation Reactions Phosphorylation  Formation of a high energy phosphate bond  Addition of a phosphate group requires energy 1)Energy + Adenosine + Phosphate inorganic → A – P Dephosphorylation  Breaking a high energy phosphate bond  Removal of a phosphate group provides energy 1)A – P → Adenosine + Phosphate inorganic + Energy

6. Oxidation – Reduction Reactions Oxidation  The removal of electrons  This molecule is said to be “Oxidized” Reduction  The addition of electrons  This molecule is said to be “Reduced”

7. Law of Mass Action An increase in the concentration of reactants relative to a reaction’s products tends to push a reaction forward.  Example: ADP + Phosphate inorganic ↔ ATP 1)↑ADP + Phosphate inorganic → ATP An increase in the concentration of a reaction’s products relative to its reactants tends to push a reaction backward. 1)ADP + Phosphate inorganic ← ↑ATP

10. Energy for Metabolic Reactions Energy  The capacity to do work.  Energy exists in several forms and is often converted from one form to another but is never created or destroyed.  All body activities depend on the availability of chemical energy.  Most of the chemical energy in the cell is provided by Adenosine Triphosphate (ATP) 1)Oxidation  Process of combining oxygen with another chemical to release energy by removal of electrons.  Example  Oxidative Phosphorylation 2)Reduction  Adding hydrogen ions to capture chemical energy

11. Activation Energy The difference in energy from the transition state and the energy of the reactants or the products Activation Energy Barrier  The amount of energy required to push the reaction forward

13. The Role of Enzymes in Chemical Reactions Reactions take place at a certain rate.  The body carefully controls the rate of metabolic reactions.  Rate of reactions can be changed by using catalysts. 1)Catalysts speed up the rate of metabolic reactions. 2)Enzymes are catalysts for the body.

14. Enzyme  A globular (functional) protein that acts as a biological catalyst. 1)Contains special properties for regulation and catalysis (speed up) of specific chemical reactions 2)These enzymes are not being changed or used up in the process  Highly specific - control only a single chemical reaction or a small group of related reactions.

15.  Most enzymes are named according to the type of reaction they catalyze and most have names ending in the suffix -ase. 1)Examples  Oxidases catalyze oxygen reactions  Hydrolases catalyze reactions to which water is added.  Enzymes decrease the activation energy required for chemical reactions to occur.

16. Involves several components  Enzyme  Substrate or reactant molecule  Enzyme-substrate complex  Product  Unchanged enzyme 1)E + S ↔ E – S → P + E Substrate Specificity  Enzymes are specific for a particular substrate Mechanisms of Enzyme Action

17. Steps of Enzyme Action Substrates  The enzyme temporarily binds to a substance, called the substrate.  Active site 1)Specific region of the enzyme molecule where the substrate binds. Conformational change  A structural change, or change in conformation, takes place which allows the enzyme and the substrate to fit precisely together. Enzyme-Substrate complex 1)The enzyme-substrate complex undergoes an internal arrangement that forms the product. Product formation 1)The enzyme releases the product of the reaction and since it is itself unaltered it can act again to produce another product.

19. Factors that Alter Enzymes Many physical factors affect the action of enzymes.  Enzymes are proteins that can become denatured. 1)Change in pH  Increase in pH from the normal 7.4 to 7.5 (a 10% shift) will break virtually all of the hydrogen bonds in proteins.  However, a return to normal pH will allow the bonds to reform and the protein to resume its normal structure. 2)Increased body heat  Normal body heat is 37 °C but body heat greater than 45 °C begins to affect enzyme action.  Enzymes are responsible for the control of most of the chemical reactions in the body and are very sensitive to changes in homeostatic levels of all kinds

20. Glucose Oxidation The Central Reaction of Energy Metabolism  Glucose 1)The most important cellular fuel ATP: The Medium of Energy Exchange  Adenosine Triphosphate 1)Formed from the breakdown of glucose during cellular respiration 2)Nucleic acid that provides the energy needed by the cell to carry out virtually all of its functions. 3)Composed of  Adenosine, a nucleic acid  Ribose, a 5-carbon sugar  Three phosphate groups attached with high energy phosphate bonds.

22. ATP in Action ATP Synthesis  Cellular respiration 1)The process of breaking down organic molecules, such as glucose, within the cell to produce ATP.  Forms high-energy phosphate bonds ATP Hydrolysis  Ruptured phosphate bonds release large amounts of energy for the metabolic activities of the cell.  Products of the hydrolysis of ATP 1)Adenosine diphosphate (ADP) 2)Inorganic phosphate group (P i ) 3)Energy  ATP : ADP + P i + Energy

24.  ATP Reaction is reversible 1)Phosphorylation 2)Accumulation of ATP pushes the reaction backward 3)Energy is available to reattach the phosphate and re-form the high energy bonds.  Without ATP, the cell is unable to carry on any work and life processes stop.

25. Stages of Glucose Oxidation Involves Glycolysis, the Krebs Cycle, and Oxidative Phosphorylation  Glycolysis 1)Breakdown of glucose. 2)Occurs on the cytosol of cells. 3)Anaerobic process, does not require oxygen. 4)Produces  2 ATP  2 NADH + 2 H +  2 Pyruvate molecules  In the (relative) absence of oxygen, lactic acid is formed  Lactic acid is produced as a metabolic by product.  Quickly diffuses into blood and is converted to pyruvic acid by the liver.

27. The Krebs Cycle Aerobic Respiration  The sequence of metabolic reactions that take place inside the mitochondria in the presence of oxygen.  2 Pyruvic acid molecules 1)Formed from 2 lactic acid molecules in the presence of oxygen. 2)2 CO 2 molecules 3)2 Acetyl CoA molecules  Formed from 2 pyruvic acid molecules inside the mitochondria  Carries acetic (citric) acid into the Citric Acid Cycle.  Citric Acid Cycle 1)Also known as the Krebs Cycle 2)Series of metabolic reactions catalyzed by many enzymes inside the mitochondria. 3)For each glucose molecule, end products are  2 ATP  6 CO 2  16 Hydrogen atoms loaded onto hydrogen carriers FAD and NAD

29. Oxidative Phosphorylation Substrate Level Phosphorylation  Electron Transport Chain 1)Another series of metabolic reactions that occur on the inner mitochondrial membrane. 2)Requires oxygen. 3)Electrons are unloaded from their carriers to oxygen, the final electron acceptor. 4)End products are  Water  32 - 34 ATP

34. Conversion of Pyruvate to Lactic Acid Because O 2 is the ultimate electron acceptor in oxidative phosphorylation, it must be continuously supplied to tissues for glucose oxidation to be completed  If O 2 supply matches the tissue demand, glucose oxidation will be completed If O 2 supply is insufficient, an electron “traffic jam” occurs in the electron transport chain

35. A reduced availability of O 2 slows all ATP- producing steps in glucose oxidation  No ATP would result in cessation of life processes Conversion of Pyruvate to Lactic Acid provides alternative pathway for generating ATP when the supply of O 2 for complete glucose oxidation is insufficient

37. Energy Storage Carbohydrate storage  Glycogen Metabolism 1)Excess glucose is linked together to form long glucose chains that are stored in the liver and muscle tissue.  Gluconeogenesis 1)Formation of glucose from non-glucose substrates  Adipose 1)Excess glucose is stored in fat cells as adipose.

38. Fat Metabolism  Lipolysis 1)Breakdown of fat for use as energy  Lipogenesis 1)Formation of fat for storage of energy Protein Metabolism  Proteolysis 1)Breakdown of protein for use as energy