ATP and Energy Pathways Module 3- Metabolism and Nutrition

ATP Work requires energy Energy is produced from ATP Adenosine triphosphate has high energy bonds located between the phosphate groups When this bond is broken energy is released (which can be used in the cell)

ATP ATP -> ADP + P + Energy Hydrolyzation of ATP This is an example of an exergonic reaction This is also known as a chemical reaction Chemical reactions are typically catalyzed by enzymes ATPase All enzymes end in “ase”

Figure 2.1 4

ATP The reverse reaction also occurs in the body ADP + P + Energy -> ATP Endergonic reaction Where does this energy come from? Food we eat Carbohydrate, protein, fat Metabolic pathways

Metabolic Pathways Limited amount of ATP in the muscle cells

Metabolic Pathways 3 Main Metabolic Systems 4 Metabolic Pathways Phosphagen System Glycogen System Oxidative System 4 Metabolic Pathways Anaerobic Phosphagen (ATP-PC, Creatine Phosphate) Anaerobic Glycolysis Aerobic Aerobic Glycolysis Oxidative

Metabolic Pathways PATHWAY TYPE LOCATION SUBSTRATE Rate Limiting Step ATP-PC Anaerobic Cytoplasm Creatine Phosphate Creatine kinase Glycolysis Glucose Phosphofructo- kinase Krebs cycle Aerobic Mitochondria Acetyl CoA Isocitrate dehydrogenase Electron transport system Hydrogen delivered by NAD and FAD for oxidative phosphorylation Cytochrome oxidase

Phosphagen System Provides ATP primarily for short term, high intensity activities Is active at the start of any activity, regardless of intensity Uses the breakdown of another high energy phosphate molecule (creatine phosphate) to produce ATP ADP + Creatine Phosphate ATP + Creatine This creatine kinase reaction can produce ATP at a high rate, however, little creatine phosphate is stored Creatine Kinase

Phosphagen System At rest, the skeletal muscle concentration of creatine phosphate is 4-6x higher than ATP stores Type II muscle fibers have a higher concentration of creatine phosphate than type I fibers The phosphagen system is controlled throw the law of mass action The concentrations of reactants or products (or both) in solution will drive the direction of the reactions

Glycolysis The breakdown of carbohydrates—either glycogen stored in the muscle or glucose delivered in the blood—to resynthesize ATP Involves multiple enzymatically catalyzed reactions, thus the rate of producing ATP is slower than the phosphagen system (however the capacity is higher due to larger stores of glucose)

Glycolysis End result is pyruvate, which has two possible paths: Converted to lactate Shuttled into the mitochondria Anaerobic (fast) glycolysis Pyruvate is converted to lactate Produces ATP at a high rate but is limited in duration The formation of lactate from pyruvate is catalyzed by the enzyme lactate dehydrogenase The end result is not lactic acid Lactate is not the cause of fatigue

Anaerobic Glycolysis Glucose + 2 Pi + 2ADP 2 Lactate + 2ATP + H2O Lactate can be transported in the blood to the liver, where it is converted to glucose. This process is referred to as the Cori cycle

Cori Cycle

Glycolysis Aerobic (slow) glycolysis Occurs when pyruvate enters the mitochondria Pyruvate that enters the mitochondria is converted to acetyl- CoA Acetyl-CoA can then enter the Krebs cycle. The NADH molecules enter the electron transport system, where they can also be used to resynthesize ATP Glucose + 2Pi + 2ADP + 2NAD+ 2Pyruvate + 2ATP + 2NADH + 2H2O

Glycolysis Control of glycolysis Energy yield of glycolysis Stimulated by high concentrations of ADP, Pi, and ammonia and by a slight decrease in pH and AMP Inhibited by markedly lower pH, ATP, CP, citrate, and free fatty acids Energy yield of glycolysis Glycolysis from one molecule of blood glucose yields a net of two ATP molecules Glycolysis from muscle glycogen yields a net of three ATP molecules

The Oxidative (Aerobic) System Primary source of ATP at rest and low intensity exercise Uses primarily carbohydrate and fat as substrates (protein can be used during starvation and very long bouts of exercise)

Carbohydrate Metabolism Glucose and glycogen oxidation Metabolism of blood glucose and muscle glycogen begins with glycolysis and leads to the Krebs cycle. (Recall: If oxygen is present in sufficient quantities, the end product of glycolysis, pyruvate, is not converted to lactate but is transported to the mitochondria, where it is taken up and enters the Krebs cycl.) NADH and FADH2 molecules transport hydrogen atoms to the electron transport chain, where ATP is produced from ADP

Electron Transport Chain

Fat Oxidation Triglycerides stored in fat cells can be broken down by hormone-sensitive lipase. This releases free fatty acids from the fat cells into the blood, where they can circulate and enter muscle fibers Some free fatty acids come from intramuscular sources Free fatty acids enter the mitochondria, are broken down, and form acetyl-CoA and hydrogen protons The acetyl-CoA enters the Krebs cycle The hydrogen atoms are carried by NADH and FADH2 to the electron transport chain

Protein Oxidation Protein is not a significant source of energy for most activities Protein is broken down into amino acids, and the amino acids are converted into glucose, pyruvate, or various Krebs cycle inter-mediates to produce ATP