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Chapter 4

Chapter 4. Operating a Cell: Enzymes, Metabolism, and Cellular Respiration. 0. Enzymes and Metabolism. Enzymes Proteins that catalyze (speed up) chemical reactions in a cell the enzyme speeds up the reaction BUT IS NOT CONSUMED IN THE REACTION

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Chapter 4

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  1. Chapter 4 Operating a Cell: Enzymes, Metabolism, and Cellular Respiration 0

  2. Enzymes and Metabolism Enzymes Proteins that catalyze (speed up) chemical reactions in a cell the enzyme speeds up the reaction BUT IS NOT CONSUMED IN THE REACTION Metabolism: all chemical reactions occurring in the body organized into distinct metabolic pathways Enzyme 2 Enzyme 3 Enzyme 1 D A C B Reaction 2 Reaction 3 Reaction 1 Startingmolecule Product

  3. Enzymes and Metabolism Enzymes Enzymes work by lowering the activation energyneeded for a reaction activation energy – initial energy you need to put into the system to start the reaction

  4. Enzymes and Metabolism Substrates are the substances being catalyzed by the enzyme enzymes bind a substrate at the active site active site has a unique shape – fits the substrate specifically now know that the binding of the substrate to the active site causes a shape change to the active site called induced fit Specificity of the enzyme to the substrate is based on enzyme shape and active site

  5. Animation: Enzymes Click “Go to Animation” / Click “Play”

  6. Metabolism Types of metabolic reactions reactions in which the potential energy of the products is lower than that of the reactants are called exergonic these reactions release energy into the system those exergonic reactions release some of their energy in the form of heat = exothermic reaction those reactions in which the potential energy of the products is greater than that of the reactants are called endergonic these reactions require energy input those reactions that require the input of heat = endothermic your metabolism is a combination of exothermic and endothermic reactions are coupled together i.e. the exothermic reactions provide the energy to drive the endothermic reactions Exergonic reaction: energy released, spontaneous Reactants Amount of energyreleased Energy Free energy Products Progress of the reaction Endergonic reaction: energy required, nonspontaneous Products Amount of energyrequired Energy Free energy Reactants Progress of the reaction

  7. ATP running all of your metabolic pathways takes energy usually in the form of ATP ATP = ribose sugar + adenine base + 3 phosphate groups the breaking of one phosphate bond between 2 phosphate groups releases potential energy into the system used by the cell to power the endergonic reactions of metabolism as we breakdown food – use the potential energy in food chemicals to produce ATP e.g. breakdown glucose to make ATP 160 kg of ATP per day! ATP  ADP + Pi + energy phosphate bonds

  8. ATP the energy released from breaking down ATP can power different kinds of work in the cell

  9. Metabolism we need a way of quantifying the energy required to drive metabolism (i.e. to perform cellular work)  calorie a calorie is the amount of energy required to raise the temperature of 1 gram of water by 1C. 1000 calories  1 kilocalorie or Calorie the breaking of one phosphate bond between 2 phosphate groups of ATP releases 7300 calories (7.3 kcal) of energy into the system

  10. Metabolism kilocalorie (kcal) or Calorie: unit of energy represented on food labels “Calories are consumed by cells to do work” cell uses the potential energy in found to do work – by making ATP we quantify that potential energy as calories Extra calories can be stored as fat 3,555 Calories = 1 pound of fat Metabolic rate: the rate at which the body uses energy

  11. Enzymes and Metabolism metabolic rate = rate at which your body uses energy can be measured as the number of calories it takes to power your metabolism Basal Metabolic Rate or BMR = represents the resting energy of a awake, resting but alert person energy used to power the vital organs – 70% of our total energy needs 70 Calories/hour or 1680 Calories/day for an average male Metabolic rate is influenced by many factors: Body weight, sex, exercise, genetic makeup, age, and nutritional status numerous equations can be used to calculate BMR and the number of Calories to be taken in per day

  12. Cellular Respiration Cellular respiration is a series of enzymatic reactions that converts energy from food into energy stored in ATP. ATP synthesis is performed in the cytoplasm = fermentation also takes place in the mitochondria = aerobic respiration

  13. Cellular Respiration when a phosphate group is transferred from ATP to another molecule (phosphorylation) - energy is transferred and ADP is produced.

  14. Cellular Respiration as ATP is used in the cell it must be replenished by cellular respiration. Aerobic cellular respiration occurs in the mitochondria and requires the presence of oxygen. C6H12O6 + 6O2 6CO2 + 6H2O + 36 ATP

  15. Animation: Glucose Metabolism Click “Go to Animation” / Click “Play”

  16. Aerobic Respiration occurs in four complex steps starting in the cytosol of the cell and completing in the mitochondria. 1. Glycolysis – cytosol 2. Transition step – mitochondria 3. Kreb’s cycle 4. Electron Transport Chain (ETC) & ATP synthesis

  17. Step 1: Glycolysis 6-carbon glucose molecule is broken down into two 3-carbon pyruvic acid molecules (i.e. pyruvate) Takes place in the cytosol and doesn’t require oxygen and produces 2 ATP two molecules of an electron acceptor called NAD+are used these pick up the electrons and hydrogen ions released during glycolysis to become NADH NADH carries 2 electrons and 2 protons NADH with its electrons will enter into mitochondria End result: 2 ATP 2 NADH 2 pyruvates

  18. Step 2: Transition Step pyruvate is brought into the mitochondria and chemically converted – IF O2 IS PRESENT mitochondria composition a. outer membrane b. inner membrane folded into cristae c. center of the mitochondria = matrix 2 pyruvates are converted into 2 molecules of acetyl coA by the enzymes of the mitochondrial matrix matrix: 2 pyruvate  2 acetyl coA + 2 CO2 + 2NADH make 2 more molecules of NADH Pyruvate CO2 End result: 2 CO2 2 NADH 2 acetyl coA NAD CoA NADH + H Acetyl CoA CoA x2

  19. Step 3: Citric Acid Cycle Citric acid cycle: series of chemical reactions catalyzed by 8 different enzymes in the mitochondrial matrix named this because one product in this cycle is citric acid also called the Kreb’s cycle cycle runs twice – once for each molecule of acetyl coA made the result is the generation of 2 ATP, 6 NADH, 2 FADH2 and the release of 4 molecules of carbon dioxide Acetyl CoA CoA Citricacidcycle 2 CO2 FADH2 3 NAD x2 End result: 2 ATP 6 NADH 2 FADH2 4 CO2 3 NADH FAD + 3 H ADP + P i ATP

  20. Step 4: Electron Transport and ATP Synthesis Electron transport chain acts like a conveyor belt, moving electrons through a series of proteins three protein complexes in the cristae of the mitochondria NADH and FADH2 drop off their electrons and hydrogen ions to these complexes the protein carriers move the electrons through the chain: 1  2  3 turns these complexes into proton pumps pump the hydrogen into the space between the inner and outer membranes (intermembrane space) the concentration of H+ ions increases within the intermembrane space H+ GRADIENT

  21. Step 4: Electron Transport Chain and ATP Synthesis H+ ions are charged, and can’t simply diffuse back across the membrane into the matrix they must pass through a protein channel called ATP synthase – generating ATP as they do as H+ ions diffuse through ATP synthase = ADP + P  ATP the ETC generates 34 ATP molecules for every pair of pyruvate that enters the mitochondria add this to the 2 ATP made from cytosolic glycolysis = 36 ATP per glucose at the end of the chain, the electrons combine with oxygen to produce water. Ultimate electron acceptor = oxygen End result: 34 ATP made from NADH and FADH2

  22. BioFlix: Cellular Respiration

  23. Cellular Respiration - Metabolism of Other Nutrients Proteins and fats can also provide energy when carbohydrates are unavailable. They are broken down and their subunits feed into aerobic cellular respiration.

  24. Anaerobic respiration: uses something other than O2 to accept electrons done by bacteria Fermentation takes place in the cytosol and does not require O2 to make ATP first series of reactions in aerobic respiration produces CO2 and lactic acid – done by bacteria, yeast and also in animal cells (e.g. muscle in humans) C6H12O6  2 pyruvate + 2 ATP  lactate (lactic acid) if O2 is present – don’t make lactic acid – pyruvate is brought into the mitochondria to finish aerobic respiration Cellular Respiration - Metabolism Without Oxygen: Anaerobic Respiration and Fermentation

  25. Cellular Respiration - Metabolism Without Oxygen: Anaerobic Respiration and Fermentation Bacteria in yogurt also use fermentation to make lactic acid. Yeast cells use fermentation to convert glucose to ethanol.

  26. Body Fat and Health Difficult to define “overweight” precisely Women need more body fat to maintain fertility than men do Average healthy body fat percentages: Women: 22% and Men: 14% Body Mass Index (BMI): correlates amount of body fat with risk of illness and death, using both height and weight Healthy range of BMI = 20-25 Obesity: BMI of 30 or higher

  27. Body Fat and Health

  28. Body Fat and Health Risk of obesity is influenced by both lifestyle (diet, exercise) and genetics Obesity increases risks of: Diabetes Hypertension Heart disease Stroke Joint problems

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