Respiration

1. Respiration

2. respiration • This is the release of energy from food. • Different from gas exchange or breathing. • Respiration occurs in cells, in the cytoplasm and the mitochondria.

3. Sources of energy • We get energy from carbohydrates, lipids and proteins.

4. An analogy • The energy in the food we eat is a $100 bill, if you tried to buy a box of matches or some gum, you would be asked for something smaller like a $5 bill. • The glucose in the food we eat is the $100 and the smaller $5 is ATP (adenosine triphosphate).

5. Atp – the universal energy carrier • This carries the energy to power all metabolic reactions in living things. • ATP and ADP (Adenosine diphosphate) are very similar, ATP carries the energy, while ADP is an empty carrier. • The energy is carried in the 3rd phosphate bond. • When ATP gives up energy it loses a phosphate to become ADP.

6. ATP Cont • The ADP then goes back into the cytoplasm and the mitochondria to be recharged.

7. The energy cycle

8. NAD – the Hydrogen Carrier • Most of the energy used to charge up ATP comes from the hydrogen in glucose. • The carbon dioxide formed is a waste product which is exhaled. • The Hydrogen from various steps needs to be carried to where it is needed, this is done by a hydrogen carrier NAD (nicotinamide adenine dinucleotide)

9. NAD – the Hydrogen Carrier H2 NAD NADH2 H2

10. NAD cont • NAD is a coenzyme, which uses one of the B complex vitamins in its structure. If this is missing from the diet, an animal will become deficient in NAD. • Respiration will be affected and the animal will always be tired. • In humans the deficiency disease is pellagra, symptoms include dermatitis, diarrhoea, mental disturbance, muscular weakness and fatigue.

11. FAD • Flavin adenine dinucleotide. • Another hydrogen carrier involved in the Kreb’s cycle.

12. Co-enzyme A • An acetyl group is formed in glycolysis. • This has to be carried to the next step by a carrier called co-enzyme A. Acetyl Acetyl Co-A Co-A Acetyl

13. aerobic Respiration • This requires oxygen. C6H12O6 + 6O2 6CO2 + 6H2O + ATP

14. Glycolysis • Takes place in the cytoplasm. • Needs 2 ATP to kick start. • The process charges 4 ATP so there is a net gain of 2 ATP. • Glucose is converted into 2 molecules of a 3C pyruvate. • 2 NADs pick up Hydrogen to become NADH2. These are carried off to the mitochondrial membranes and the electron transport chain. • No oxygen is needed in glycolysis.

15. Glycolysis Glucose NAD 2 ADP To electron transport chain NADH2 2 ATP Anaerobic Anaerobic pathway 2 Pyruvate Aerobic pathway

16. Formation of Acetyl Co-enzyme a • The pyruvate loses a C (forming CO2) to become a 2C acetyl group. • This is carried by Co-A to the Kreb’s Cycle. • This takes place in the matrix of the mitochondria. • The Co-A drops off the acetyl group, then goes back to the end of glycolysis to pick up more acetyl groups.

17. Formation of Acetyl Co-enzyme a Pyruvate (C3) 2NADH2 CO2 Acetyl Co-A (C2) Co-A The Kreb’s Cycle

18. The kreb’s cycle • This takes place in the inner matrix of the mitochondria. • In a complex series of chemical reactions, the acetyl group joins with other chemicals in a returning cycle. • CO2 is released and a small amount of ATP is produced. • Many NADs are charged to form NADH2, which are carried to the electron transfer system.

19. Kreb’s cycle (citric acid cycle) Acetyl Co-A (C2) To electron transport chain To electron transport chain C4 Citric Acid (C6) ADP NADH2 ATP NAD CO2 NAD CO2 C5 NADH2

20. The electron transfer system or respiratory chain • This is located on the membranes or cristae of the mitochondria. • The system consists of a row of cytochromes, which pass hydrogen electrons down from one to the other. • This results in a series of oxidation and reduction reactions which release about 3 ATPs for every hydrogen involved. • One molecule of glucose can charge up to 38 molecules of ATP.

21. The electron transfer system or respiratory chain • Think of the cytochromes as a row of springs, the electrons bounce down the springs. • Each bounce gives off energy to help charge up ADP to form ATP. • At the end of this stage the low energy hydrogen joins with oxygen and forms water.

22. Anaerobic respiration or fermentation • If there is no oxygen, the electron transport system blocks up, the Kreb’s Cycle jams up and so on. Another acceptor has to be found for all the hydrogen. • In the absence of oxygen, glycolysis can still occur. • Different things happen in plants and animals.

23. Anaerobic Metabolism in Plants • Ethyl alcohol and carbon dioxide are given off. • The NAD is cleared to pick up some more hydrogen. Pyruvate + NAHD2 ethanol + Carbon dioxide + NAD + 2 ATP • Quite common in bacteria, fungi such as yeast, and the seeds of some plants e.g. peas

24. Anaerobic Metabolism in animals • The hydrogen is passed to the pyruvate, and the end product is lactic acid. • The NAD is cleared to keep this cycle of glycolysis going. Pyruvate + NAHD2 lactic acid + NAD + 2 ATP

25. Summarising anaerobic respiration Glucose 2ADP 2ATP Pyruvate NADH2 NADH2 NAD NAD Plants Animals Lactic Acid Ethanol + Carbon Dioxide

26. Factors that can affect respiration • The process of respiration is run by enzymes, so anything which affects enzyme action will affect respiration. • Temperature • pH • Enzyme and substrate concentration • Can be poisoned

27. Factors that can affect respiration • An energy source is needed (glucose, fats or proteins.) • Sufficient oxygen is needed • Carbon dioxide must not be allowed to accumulate or it will slow respiration down. • With anaerobic metabolism, the ethanol produced can poison off yeast cells.