Bioenergetics and Cellular Chemical Reactions

1. Bioenergetics

2. Objectives • Discuss the functions of the cell membrane, nucleus, and mitochondria. • Define the following terms: (1) endergonic reactions, (2) exergonic reactions, (3) coupled reactions, and (4) bioenergetics. • Describe the role of enzymes as catalysts in cellular chemical reactions. • List and discuss the nutrients that are used as fuels during exercise. • Identify the high-energy phosphates.

3. Objectives • Discuss the biochemical pathways involved in anaerobic ATP production. • Discuss the aerobic production of ATP. • Describe the general scheme used to regulate metabolic pathways involved in bioenergetics. • Discuss the interaction between aerobic and anaerobic ATP production during exercise. • Identify the enzymes that are considered rate limiting in glycolysis and the Krebs cycle.

4. Cell Structure Biological Energy Transformation Cellular Chemical Reactions Oxidation-Reduction Reactions Enzymes Fuels for Exercise Carbohydrates Fats Proteins Outline • Control of Bioenergetics • Control of ATP-PC System • Control of Glycolysis • Control of Krebs Cycle and Electron Transport Chain • Interaction Between Aerobic/Anaerobic ATP Production • High-Energy Phosphates • Bioenergetics • Anaerobic ATP Production • Aerobic ATP production • Aerobic ATP Tally • Efficiency of Oxidative Phosphorylation

5. Introduction • Metabolism • Sum of all chemical reactions that occur in the body • Anabolic reactions • Synthesis of molecules • Catabolic reactions • Breakdown of molecules • Bioenergetics • Converting foodstuffs (fats, proteins, carbohydrates) into energy

6. Cell Structure Cell Structure • Cell membrane • Semipermeable membrane that separates the cell from the extracellular environment • Nucleus • Contains genes that regulate protein synthesis • Molecular biology • Cytoplasm • Fluid portion of cell • Contains organelles • Mitochondria

7. Cell Structure A Typical Cell and Its Major Organelles Figure 3.1

8. Cell Structure In Summary • Metabolism is defined as the total of all cellular reactions that occur in the body; this includes both the synthesis of molecules and the breakdown of molecules. • Cell structure includes the following three major parts: (1) cell membrane, (2) nucleus, and (3) cytoplasm (called sarcoplasm in muscle). • The cell membrane provides a protective barrier between the interior of the cell and the extracellular fluid. • Genes (located within the nucleus) regulate protein synthesis within the cell. • The cytoplasm is the fluid portion of the cell and contains numerous organelles

9. Cell Structure A Closer Look 3.1Molecular Biology and Exercise Science • Study of molecular structures and events underlying biological processes • Relationship between genes and cellular characteristics they control • Genes code for specific cellular proteins • Process of protein synthesis • Exercise training results in modifications in protein synthesis • Strength training results in increased synthesis of muscle contractile protein • Molecular biology provides “tools” for understanding the cellular response to exercise

10. Biological Energy Transformation Steps Leading to Protein Synthesis DNA contains information to produce proteins. Transcription produces mRNA. mRNA leaves nucleus and binds to ribosome. Amino acids are carried to the ribosome by tRNA. In translation, mRNA is used to determine the arrangement of amino acids in the polypeptide chain. Figure 3.2

11. Biological Energy Transformation Cellular Chemical Reactions • Endergonic reactions • Require energy to be added • Endothermic • Exergonic reactions • Release energy • Exothermic • Coupled reactions • Liberation of energy in an exergonic reaction drives an endergonic reaction

12. Biological Energy Transformation The Breakdown of Glucose: An Exergonic Reaction Figure 3.3

13. Biological Energy Transformation Coupled Reactions The energy given off by the exergonic reaction powers the endergonic reaction Figure 3.4

14. Biological Energy Transformation Oxidation-Reduction Reactions • Oxidation • Removing an electron • Reduction • Addition of an electron • Oxidation and reduction are always coupled reactions • Often involves the transfer of hydrogen atoms rather than free electrons • Hydrogen atom contains one electron • A molecule that loses a hydrogen also loses an electron and therefore is oxidized • Importance of NAD and FAD

15. Biological Energy Transformation Oxidation-Reduction Reaction Involving NAD and NADH Figure 3.5

16. Biological Energy Transformation Enzymes • Catalysts that regulate the speed of reactions • Lower the energy of activation • Factors that regulate enzyme activity • Temperature • pH • Interact with specific substrates • Lock and key model

17. Biological Energy Transformation Enzymes Catalyze Reactions Enzymes lower the energy of activation Figure 3.6

18. Biological Energy Transformation The Lock-and-Key Model of Enzyme Action Substrate (sucrose) approaches the active site on the enzyme. Substrate fits into the active site, forming enzyme-substrate complex. The enzyme releases the products (glucose and fructose). Figure 3.7

19. Biological Energy Transformation Clinical Applications 3.1Diagnostic Value of Measuring Enzyme Activity in the Blood • Damaged cells release enzymes into the blood • Enzyme levels in blood indicate disease or tissue damage • Diagnostic application • Elevated lactate dehydogenase or creatine kinase in the blood may indicate a myocardial infarction

20. Biological Energy Transformation Examples of the Diagnostic Value of Enzymes in Blood

21. Biological Energy Transformation Classification of Enzymes • Oxidoreductases • Catalyze oxidation-reduction reactions • Transferases • Transfer elements of one molecule to another • Hydrolases • Cleave bonds by adding water • Lyases • Groups of elements are removed to form a double bond or added to a double bond • Isomerases • Rearrangement of the structure of molecules • Ligases • Catalyze bond formation between substrate molecules

22. Biological Energy Transformation Example of the Major Classes of Enzymes

23. Biological Energy Transformation Factors That Alter Enzyme Activity • Temperature • Small rise in body temperature increases enzyme activity • Exercise results in increased body temperature • pH • Changes in pH reduces enzyme activity • Lactic acid produced during exercise

24. Biological Energy Transformation The Effect of Body Temperature on Enzyme Activity Figure 3.8

25. Biological Energy Transformation The Effect of pH on Enzyme Activity Figure 3.9

26. Fuels for Exercise Carbohydrates • Glucose • Blood sugar • Glycogen • Storage form of glucose in liver and muscle • Synthesized by enzyme glycogen synthase • Glycogenolysis • Breakdown of glycogen to glucose

27. Fuels for Exercise Fats • Fatty acids • Primary type of fat used by the muscle • Triglycerides • Storage form of fat in muscle and adipose tissue • Breaks down into glycerol and fatty acids • Phospholipids • Not used as an energy source • Steroids • Derived from cholesterol • Needed to synthesize sex hormones

28. Fuels for Exercise Protein • Composed of amino acids • Some can be converted to glucose in the liver • Gluconeogenesis • Others can be converted to metabolic intermediates • Contribute as a fuel in muscle • Overall, protein is not a primary energy source during exercise

29. Fuels for Exercise In Summary • The body uses carbohydrate, fat, and protein nutrients consumed daily to provide the necessary energy to maintain cellular activities both at rest and during exercise. During exercise, the primary nutrients used for energy are fats and carbohydrates, with protein contributing a relatively small amount of the total energy used. • Glucose is stored in animal cells as a polysaccharide called glycogen. • Fatty acids are the primary form of fat used as an energy source in cells. Fatty acids are stored as triglycerides in muscle and fat cells.

30. High-Energy Phosphates ATP ADP + Pi+ Energy ATPase High-Energy Phosphates • Adenosine triphosphate (ATP) • Consists of adenine, ribose, and three linked phosphates • Synthesis • Breakdown ADP + Pi ATP

31. High-Energy Phosphates Structure of ATP Figure 3.10

32. High-Energy Phosphates Model of ATP as the Universal Energy Donor Figure 3.11

33. Bioenergetics Bioenergetics • Formation of ATP • Phosphocreatine (PC) breakdown • Degradation of glucose and glycogen • Glycolysis • Oxidative formation of ATP • Anaerobic pathways • Do not involve O2 • PC breakdown and glycolysis • Aerobic pathways • Require O2 • Oxidative phosphorylation

34. Bioenergetics ATP + C PC + ADP Creatine kinase Anaerobic ATP Production • ATP-PC system • Immediate source of ATP • Glycolysis • Glucose  2 pyruvic acid or 2 lactic acid • Energy investment phase • Requires 2 ATP • Energy generation phase • Produces 4 ATP, 2 NADH, and 2 pyruvate or 2 lactate

35. Bioenergetics The Winning Edge 3.1Does Creatine Supplementation Improve Exercise Performance? • Depletion of PC may limit short-term, high-intensity exercise • Creatine monohydrate supplementation • Increased muscle PC stores • Some studies show improved performance in short-term, high-intensity exercise • Inconsistent results may be due to water retention and weight gain • Increased strength and fat-free mass with resistance training • Creatine supplementation does not appear to pose health risks

36. Bioenergetics A Closer Look 3.2Lactic Acid or Lactate? • Terms lactic acid and lactate used interchangeably • Lactate is the conjugate base of lactic acid • Lactic acid is produced in glycolysis • Rapidly disassociates to lactate and H+ The ionization of lactic acid forms the conjugate base called lactate Figure 3.12

37. Bioenergetics The Two Phases of Glycolysis Figure 3.13

38. Bioenergetics Interaction Between Blood Glucose and Muscle Glycogen in Glycolysis Figure 3.14

39. Bioenergetics Glycolysis: Energy Investment Phase Figure 3.15

40. Bioenergetics Glycolysis: Energy Generation Phase Figure 3.15

41. Bioenergetics Hydrogen and Electron Carrier Molecules • Transport hydrogens and associated electrons • To mitochondria for ATP generation (aerobic) • To convert pyruvic acid to lactic acid (anaerobic) • Nicotinamide adenine dinucleotide (NAD) • Flavin adenine dinucleotide (FAD) NAD + 2H+ NADH + H+ FAD + 2H+ FADH2

42. Bioenergetics A Closer Look 3.3NADH is “Shuttled” into Mitochondria • NADH produced in glycolysis must be converted back to NAD • By converting pyruvic acid to lactic acid • By “shuttling” H+ into the mitochondria • A specific transport system shuttles H+ across the mitochondrial membrane • Located in the mitochondrial membrane

43. Bioenergetics Conversion of Pyruvic Acid to Lactic Acid The addition of two H+ to pyruvic acid forms NAD and lactic acid Figure 3.16

44. Bioenergetics ATP ADP + Pi+ Energy ATPase In Summary • The immediate source of energy for muscular contraction is the high-energy phosphate ATP. ATP is degraded via the enzyme ATPase as follows: • Formation of ATP without the use of O2 is termed anaerobic metabolism. In contrast, the production of ATP using O2 as the final electron acceptor is referred to as aerobic metabolism.

45. Bioenergetics In Summary • Exercising skeletal muscles produce lactic acid. However, once produced in the body, lactic acid is rapidly converted to its conjugate base, lactate. • Muscle cells can produce ATP by any one or a combination of three metabolic pathways: (1) ATP-PC system, (2) glycolysis, (3) oxidative ATP production. • The ATP-PC system and glycolysis are two anaerobic metabolic pathways that are capable of producing ATP without O2.

46. Bioenergetics Aerobic ATP Production • Krebs cycle (citric acid cycle) • Pyruvic acid (3 C) is converted to acetyl-CoA (2 C) • CO2 is given off • Acetyl-CoA combines with oxaloacetate (4 C) to form citrate (6 C) • Citrate is metabolized to oxaloacetate • Two CO2 molecules given off • Produces three molecules of NADH and one FADH • Also forms one molecule of GTP • Produces one ATP

47. Bioenergetics The Three Stages of Oxidative Phosphorylation Figure 3.17

48. Bioenergetics The Krebs Cycle Figure 3.18

49. Bioenergetics Fats and Proteins in Aerobic Metabolism • Fats • Triglycerides  glycerol and fatty acids • Fatty acids  acetyl-CoA • Beta-oxidation • Glycerol is not an important muscle fuel during exercise • Protein • Broken down into amino acids • Converted to glucose, pyruvic acid, acetyl-CoA, and Krebs cycle intermediates

50. Bioenergetics Relationship Between the Metabolism of Proteins, Carbohydrates, and Fats Figure 3.19