Energy and Respiration

1. Energy and Respiration

2. The need for energy in living organisms • continuous supply of energy for: • Synthesis of complex substances from simpler ones (anabolic reactions) • Active transport • Mechanical work – movement • Maintenance of internal body temperature

3. ATP • Adenosine triphosphate • Energy released is not then directly used, it is passed on to ATP. • ATP is made of: • Adenine • Ribose • 3 phosphate molecules

5. When a phosphate group is removed from ATP, ADP is formed and energy is released. • ATP + H2O = ADP + H3PO4 ± 30.5kJ • ATP is the universal intermediary molecule. It is known as the energy currency.

6. Synthesis of ATP • Two ways: (see page 199) 1. energy released by reorganising chemical bonds. 2. using electrical potential energy when electrons are transferred by electron carriers. This is called chemiosmosis.

7. Respiration • Organic molecules are broken down to release energy to make ATP. • Two types: A) Aerobic respiration – in the presence of oxygen. B) Anaerobic respiration – in the absence of oxygen. • Both start with glycolysis.

9. Glycolysis • Phosphorylation (adding phosphate) of glucose using ATP • Occurs in the cytoplasm. • Splitting hexose phosphate (6C) into two triose phosphate molecules (3C) • These are then oxidised, releasing ATP and reducing NAD

10. Nicotinamide Adenine Diphosphate NAD Consists of two nucleotides joined by their phosphate groups Transfers electrons during respiration reactions

11. Glucose (hexose) (6C) Hexose phosphate (6C) produced by phosphorylation using ATP Hexose bisphosphate (6C) adding another phosphate using ATP This splits into two 2 molecules of triose phosphate (3C) A sequence of Intermediate molecules are formed, by reducing NAD and losing phosphates to produce 4 molecules of ATP 2 x Pyruvate (3C)

12. GLUCOSE (6C) 2ATP 2ADP 2 ATP USED HEXOSE BIPHOSPHATE TRIOSE PHOSPHATE (3C) TRIOSE PHOSPHATE (3C) NAD+ NADH NAD+ NADH 2ADP 2ATP 2ADP 2ATP PYRUVATE 4 ATP PRODUCED PYRUVATE

14. Link reaction • Occurs when oxygen available • Pyruvate enters the mitochondrion by active transport. • It is decarboxylated (carbon removed) • Dehydrogenated (hydrogen removed) • As a result of this, CO2 is formed and NAD is reduced

16. Krebs cycle • Closed pathway of enzyme-controlled reactions • Occurs in matrix of mitochondria • Acetyl CoA (2C) enters the cycle and joins with a 4 carbon compound to make a 6 carbon compound. • A series of steps now transfer the 6C (citrate) back to the 4C (oxaloacetate) • These steps include more decarboxylation and dehydrogenation

17. Pg 203

18. LINK REACTION. Pyruvate molecules (3-carbon) from glycolysis are converted into another type of molecule called Acetyl-CoA in a process known as pyruvic oxidation. This conversion occurs when the pyruvate is broken down by a complex of 3 enzymes called pyruvate dehydrogenase, releasing a carbon atom which goes on to form carbon dioxide (CO2).The 2 remaining carbon molecules bond with coenzyme A forming Acetyl-CoA. During this process, electrons and a hydrogen ion are passed to NAD+, thus oxidizing the pyruvate, hence the name of the process.

19. Step 1. The Acetyl-CoA then enters the Krebs cycle. It initially combines with a 4-carbon molecule called oxoaloacetic acid, forming a 6-carbon molecule of citric acid (citrate).This reaction is catalyzed by the enzyme citrate synthase.  Upon this formation, the coenzyme A is released, returning to the link reaction.

20. Step 2. The citrate molecule is then dehydrated (H20 molecule is removed) and then rehydrated by the enzyme aconitase. The resulting molecule is just a rearranged form of citrate known as isocitrate.

21. Step 3. Next, isocitrate undergoes what is known as a oxidative carboxylation, which simply means that a carbon and hydrogen are given off. The result of this is a 5-carbon molecule called alpha-ketoglutarate. This process is catalyzed by the enzyme isocitrate dehydrogenase. Additionally, the carbon that broke off forms CO2, while the hydrogen reduces NAD+ to form NADH.

22. Step 4. In the next reaction, alpha-ketoglutarate has yet another carbon molecule removed and is then transferred to a CoA molecule by the enzyme alpha-ketoglutarate dehydrogenase. The resulting product is a 4-carbon molecule of Succinyl-CoA. Additionally, CO2 and NADH is formed.

23. Step 5. After succinyl-CoA is formed, the molecule then undergoes the removal of the CoA carrier, resulting in the production of succinate. Additionally, the enzyme succinyl-CoA synthetase that removes the CoA also produces GTP (Guanosine Triphosphate) through substrate level phosphorylation (phosphate molecule directly added to another molecule). (GTP is a high energy molecule similar to ATP, and later an ADP molecule takes the phosphate from GTP and makes ATP)

24. Step 6. Next, succinate is dehydrated by the enzyme succinate dehydrogenase. The resulting product is furmate. Step 7. Furmate is then hydrated (water added) by enzyme furmase to form malate Step 8. Lastly, the malate is dehydrogenated by the enzyme malate dehydrogenase, forming the original molecule oxaloacetate. From this reaction, NADH and H+ are also produced.

25. SUMMARY Every pyruvate molecule that enters the Krebs cycle generates 3 molecules of CO2, one molecule of ATP, one molecule of FADH and 4 molecules of NADH ADP+P ATP Pyruvate 3CO2 4NAD+ 4NADH FAD+ FADH The reduced NAD and FAD molecules enter the electron transfer chain, and result in a large number of ATP molecules being produced.

26. Electron Transport Chain • NADH and FADH2oxidised - electron and proton released • electron picked up by an electron carrier on the inner membrane • It is passed from one acceptor to another along a chain. • electron has a high potential energy at beginning of chain but as it is passed along the electron falls to a lower energy state. • energy released actively pumps the hydrogen ion (proton) into the intermembrane space.

27. electron reaches the end of the chain it rejoins to the hydrogen ion to make a hydrogen atom. • These hydrogen atoms then join to oxygen to form water.

29. Chemiosmosis • hydrogen ions actively transported into the intermembrane space. • Chemiosmosis is the movement of ions across a selectively-permeable membrane, down their electrochemical gradient.

31. concentration of hydrogen ions in the intermembrane space builds up so diffusion occurs. • The hydrogen ions move through a protein channel and as they move they provide energy for ATP synthase to join ADP and P to make ATP.

37. - If there is no oxygen there is no where for the hydrogen to go - which then blocks the electron transport chain - which stops the NAD from being regenerated - so the krebs cycle is blocked - so the link reaction is blocked - and only glycolysis can occur – anaerobic respiration.

38. Anaerobic Respiration • To regenerate NAD to be able to continue glycolysis, pyruvate becomes the hydrogen acceptor. • This either forms lactic acid or ethanol. • In animals end product is lactic acid C6H12O6→ 2CH3CH(OH)COOH + 2 ATP • In plants and yeast end product is ethanol and carbon dioxide C6H12O6→ 2CH3CH2OH + CO2 + 2ATP

39. Lactic acid is produced just by adding 2 hydrogen molecules to pyruvate. • Ethanol is produced by first removing a carbon molecule (releasing carbon dioxide) and then adding the 2 hydrogen molecules. That is why alcoholic fermentation is accompanied by evolution of carbon dioxide.

40. What happens to the products of anaerobic respiration? • Both lactic acid and ethanol contain a lot of energy. • In animals this energy can be released by changing lactic acid back to pyruvate and then pyruvate continuing on the rest of the aerobic respiration pathways. • This requires oxygen to unblock the ETC and Krebs cycle • The amount of oxygen required to do this is called the oxygen debt.

42. Plants cannot use the ethanol. • It cannot be converted back into pyruvate and it cannot be oxidised • The ethanol is toxic and if anaerobic respiration continues for too long the plant will be poisoned and die. • Seeds and plants growing in waterlogged conditions can respire anaerobically for a short time.

43. Respiratory Quotient • It is a unitless number used in calculations of basal metabolic rate (BMR) • It is the ratio of the volume of carbon dioxide released to the volume of oxygen consumed by a body tissue or an organism in a given period.

44. The respiratory quotient (RQ) is calculated from the ratio: • RQ = CO2 eliminated / O2 consumed • The range of respiratory coefficients for organisms in metabolic balance usually ranges from 1.0 (representing the value expected for pure carbohydrate oxidation) to ~0.7 (the value expected for pure fat oxidation). 

45. Carbohydrates • The value of RQ is equal to 1 if carbohydrates are the respiratory substrates in aerobic respiration. • Fats • When the respiratory substrate is fat, the RQ is about 0.7. • Example: Tripalmitin • Fats contain less oxygen than carbohydrates and so they require more oxygen for oxidation. • Anaerobic respiration • The value of RQ is infinity during anaerobic respiration because CO2 is produced but O2 is not utilised.

46. Measuring RQ • This is done by measuring the change in the volume of gas surrounding the material as it respires – • first as carbon dioxide is absorbed (to measure the rate of oxygen consumption) • and then without absorbing the carbon dioxide (from which you can calculate the rate of production of carbon dioxide by comparison with the first measurment). • The apparatus consists of two vessels. One vessel contains the organisms and the other acts as a thermobarometer – small changes in temperature or pressure cause air in this vessel to expand or contract, compensating for similar changes in the first vessel. Changes in the manometer level are thus due only to the activities of the respiring material.