Energy and Respiration

1. Energy and Respiration 1

2. Energy and food • The amount of energy available from a certain food is sometimes called its caloric value • The average adult requires about 8400 Kilojoules (2000 kilocalories) of energy per day • An adult male undertaking heavy physical labor may require as much as 14,700 kJ (3500 kcal) 2

3. Energy and food • Carbohydrates, proteins and fats make up most of the human diet. • The idea ratio should be approximately 60% to 30% to 10% respectively • Carbohydrates are the most readily available source of energy • Fats which are essentially non-oxidized provide the most energy per unit mass 3

4. Energy and food • The body does not “burn” food, but nevertheless it is converted to the same set of products (CO2 and H2O) through a series of oxidation reactions. • Since Hess’ Law shows that the energy change is independent of the pathway, the same amount of energy is released through burningfood. 4

5. The Bomb Calorimeter • A bomb calorimeter can be used to measure the energy content of food. • The calorific value of food can be measured by heating a pre-measured mass of food and igniting it in an oxygen atmosphere. • The heat is transferred to a water system and the heat evolved is computed from the temperature change and the mass of water A diagram of a bomb calorimeter 5

6. The Bomb Calorimeter • The calorific value of a candy bar is about 250 Dietician’s Calories or 250 kilocalories • This means that if it were burned in a calorimeter, the energy produced on combustion would raise the temperature of 2.5 kg water by 100°C assuming that the calorimeter itself does not absorb any energy. • In most cases the energy absorbed by the calorimeter cannot be ignored and must be included in the calculations. A diagram of a bomb calorimeter 6

7. The Bomb Calorimeter • A large candy bar weighs 50 g. If a 5.00 g sample of the candy bar, on complete combustion raises the temperature of 500 g water in a glass container by 59.6°C. • Calculate the calorific value of the candy bar. The heat capacity of the glass calorimeter is 20.9 cal °C-1 A diagram of a bomb calorimeter 7

8. The Bomb Calorimeter A large candy bar weighs 50 g. If a 5.00 g sample of the candy bar, on complete combustion raises the temperature of 500 g water in a glass container by 59.6°C, calculate the calorific value of the candy bar. The heat capacity of the glass calorimeter is 20.9 cal °C-1 Heat produced = heat absorbed by water + heat absorbed by calorimeter = (m x C x ΔT)water + (m x C. x ΔT)calorimeter = (500 g x 1.00 cal g-1 °C-1 x 59.6 °C) + (20.9 cal °C-1 x 59.6°C) = 25,086 calories = 25.09 kcal (produced by 5.0 g of candy bar) = 5.02 kcal g-1 8

9. Respiration • Respiration is crucial function for all living organisms. • In general the process of respiration serves two basic purposes • The disposal of electrons generated during catabolism • The production of ATP. 9

10. Cellular Respiration • Cellular respiration involves a set of metabolic processes that occur in the cell to convert biochemical energy from nutrients into adenosine triphosphate (ATP) and waste products • Respiration involves catabolic redox reactions. One molecule is oxidized and another is reduced. 10

11. Adenosine Triphosphate The structure of ATP includes an adenine group, a ribose sugar, and three phosphate groups 11

12. Adenosine Triphosphate Energy released from the catabolic destruction of carbon containing molecules is stored in ATP. 12

13. ATP and ADP • Energy is released when a phosphate group is released from ATP resulting in the formation of ADP. • The reversible reaction between ATP and ADP acts much like a “battery “allowing the cell to store and release energy 13 The conversion of ATP to ADP releases about 30.5 kJ mol-1 13

14. ATP and ADP • Energy is released when a phosphate group is released from ATP resulting in the formation of ADP. • The reversible reaction between ATP and ADP acts much like a “battery “allowing the cell to store and release energy The conversion of ATP to ADP releases about 30.5 kJ mol-1 14

15. Aerobic and Anaerobic Respiration Respiration may be either aerobic or anaerobic • Aerobic respiration uses oxygen as its terminal electron acceptor, • Anaerobic respiration uses terminal electron acceptors other than oxygen 15

16. Aerobic Respiration Aerobic respiration requires oxygen • It involves the break down of glucose, amino acids and fatty acids to release energy • Oxygen is the terminal electron acceptor. • The overall process of aerobic respiration can be described as: Glucose + Oxygen →Energy + Carbon dioxide + Water 16

17. Aerobic Respiration • The aerobic respiration is a high energy yielding process. • Up to 38 molecules of ATP are produced for every molecule of glucose that is utilized. • Aerobic respiration takes place in almost all living things. • It is relatively easy for the body to get rid of the Carbon Dioxide and excess water. This is excretion (the removal of the toxic waste products of metabolism), • Maximum energy is released from the glucose. 17

18. Anaerobic Respiration • Some organisms can respire in the absence of air: this is anaerobic respiration. This does not release so much energy and it produces more toxic waste products. • When Oxygen is not available, anaerobic respiration also occurs in humans. • Anaerobic respiration can take place during vigorous exercise, building up lactic acid in muscle tissue. This results in muscle pain and cramping. • The bacteria in milk also produce lactic acid but is an optical isomer of that produced in muscle cramping. • Yeasts produce alcohol which is also toxic. Eventually there will be so much alcohol that the yeast cannot survive. 18

19. Anaerobic Respiration • Anaerobic respiration is a special type of respiration, which takes place without oxygen to produce energy in the form of ATP or adenosine tri-phosphate. • The process of anaerobic respiration for production of energy can occur in either of the ways represented below: Glucose →Energy (ATP) + Ethanol + Carbon dioxide (CO2) Glucose →Energy (ATP) + Lactic acid 19

20. Anaerobic Respiration • The process of anaerobic respiration is relatively less energy yielding than aerobic respiration • During the alcoholic fermentation or the anaerobic respiration two molecules of ATP (energy) are produced. for every molecule of glucose used in the reaction. • Likewise for lactate fermentation 2 molecules of ATP are produced for every molecule of glucose used. • Thus anaerobic respiration breaks down one glucose molecule to obtain two units of the energy storing ATP molecules. 20

21. Hemoglobin and Oxygen Transport • The ability of iron to form complexes plays an important in the transport of oxygen and carbon dioxide in the hemoglobin of the blood 21

22. Hemoglobin and Oxygen Transport • Hemoglobin is a complex protein. At certain sites within the protein are structures known as porphyrin rings. A Fe2+ion at the center of the ring attracts and transports oxygen At high oxygen concentrations (as in the lungs) hemoglobin binds to the oxygen molecules which is then carried to the cells. O2 22

23. Hemoglobin and Oxygen Transport At high carbon dioxide concentrations as are found at the cell level hemoglobin binds to the carbon dioxide molecules which are then transported back to the lungs where the carbon dioxide is released and exhaled. CO2 23

24. Hemoglobin and Oxygen Transport Poisons • Species such as carbon monoxide and cyanide ions poison hemoglobin They attach to the iron more or less permanently, making it impossible for the hemoglobin to transport carbon dioxide or oxygen 24

25. Electron Transport • The oxidation of food at the cellular level involves a series of redox reactions involving electron transport • These reactions take place in the mitochondria found inside the cell • The enzymes that catalyze these oxidation processes are called cytochromes • Cytochromes incorporate porphyrin rings with either a Cu2+ or Fe2+ at the center + 25

26. Electron Transport The cytochrome structure heme group from cytochrome oxidase Cytochromes contain Cu2+ or Fe3+ ions. The porphyrin ligand contains 4 nitrogen atoms, each of which donates 2 electrons. + During each step of the oxidation of glucose: Fe3+ Fe2+ + e- or Cu2+  Cu+ + e- 26

27. Electron Transport The cytochrome structure heme group from cytochrome oxidase. Oxidation stage of glucose C6H12O6 + 6H2O  6CO2+24H+ +24e- Fe3++ e- Fe2+ (Metal ion is reduced) + Reduction stage O2 + 4H+ +4e- 2H2O Fe2+ Fe3+ + e-(Metal ion is oxidized) Cu+  Cu2+ + e- 27