Review Questions Respiration (key)

Review Questions - Chapter 8 How

Cells Release Chemical Energy

1. What happens to the CO2 and H2O produced during acetyl-CoA formation and the Krebs cycle?

It is released to the environment (animals and plants). In plants, some of it may be used in photosynthesis.

2. No matter what the source of energy might be, organisms must convert it to ___ATP_______, a form of chemical energy that can drive metabolic reactions. 3. Give the overall equation for the aerobic respiratory route; indicate where energy occurs in the equation.

C6H12O6 + 6O2 ———> 6CO2 + 6H2O + energy (energy from this reaction is transferred to ATP, but the majority is lost as heat).

4. In the first of the three stages of aerobic respiration, __glucose________ is partially degraded to pyruvate. 5. Glycolysis occurs in the __cytoplasm________ of the cell. 6. Explain the purpose served by molecules of ATP reacting first with glucose and then with fructose-6phosphate in the early part of glycolysis (see Figure 7.4 in the text).

The ATP is “priming the pump”. That is, it is supplying activation energy for subsequent reactions.

7. Four ATP molecules are produced by __substrate_-__level________ phosphorylation for every two used during glycolysis. Consult Figure 7.4 in the text. 8. Glycolysis produces ___2_______ (number) NADH, ____2______ (number) ATP (net) and ____2______ (number) pyruvate molecules for each glucose molecule entering the reactions. 9. Consult Figures 7.4 and 7.6 in the text. State the events that happen during the preparatory steps and explain how the process of acetyl-CoA formation relates glycolysis to the Krebs cycle.

Preparatory Steps and the Krebs Cycle 1. Pyruvate enters the mitochondria and is converted to acetyl-CoA, which then joins oxaloacetate already present from a previous “turn” of the cycle. 2. During each turn of the cycle, three carbon atoms enter (as pyruvate) and three leave as three carbon dioxide molecules. 3. The pyruvate conversion to acetyl-CoA is the link from gylcolysis to the Kreb’s cycle. 1

10. Explain, in general terms, the role of oxygen in aerobic respiration.

Oxygen joins with the “spent” electrons and H+ to yield water. 11. Consult Figure 7.5 in the text and predict what will happen to the NADH produced during acetyl-CoA formation and the Krebs cycle.

This NADH enters the Electron Transfer Phosphorylation pathway were it will supply energy to support the chemo-osmotic production of ATP.

12. State which factors determine whether the pyruvate (pyruvic acid) produced at the end of glycolysis will enter into the alcoholic fermentation pathway, the lactate fermentation pathway, or the acetyl-CoA formation pathway.

Alcoholic Fermentation (Oxygen not present) a. Fermentation begins with glucose degradation to pyruvate. b. Cellular enzymes convert pyruvate to acetaldehyde, which then accepts electrons from NADH to become alcohol. c. Yeasts are valuable in the baking industry (carbon dioxide byproduct makes dough “rise”) and in alcoholic beverage production. Lactate Fermentation (Oxygen not present) a. Certain bacteria (as in milk) and muscle cells have the enzymes capable of converting pyruvate to lactate. b. No additional ATP beyond the net two from glycolysis is produced but NAD+ is regenerated. .

Acetyl-CoA Formation Pathway. a. If oxygen is present, then the pyruvate will enter the preliminary steps pathway. b. Pyruvate will react with CoA enzyme to from acetyl CoA. This in turn hands off acetyl to oxaloacetic acid to become part of the Kreb’s cycle.

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13. By the end of the second stage of aerobic respiration, which includes the ___Kreb’s_______ cycle, the carbon chain of __pyruvate________ has been partly degraded to carbon dioxide; the waste product __water________ is produced at the end of electron trasport phosphorylation. 14. Be able to account for the total net yield of thirty-six ATP molecules produced through aerobic respiration; that is, state how many ATPs are produced in glycolysis, acetyl-CoA formation, the Krebs cycle, and electron transport phosphorylation.

• Glycolysis – 2 ATP formed by substrate-level phosphorylation • Krebs cycle and preparatory reactions – 2 ATP formed by substrate-level phosphorylation • Electron transport phosphorylation – 32 ATP formed

15. Explain how chemiosmotic theory operates in the mitochondrion to account for the production of ATP molecules.

Occurs in the mitochondria (inter membrane) Coenzymes (NADH and FADH2) deliver electrons to electron transfer chains + • Electron transfer sets up H ion gradients + • Flow of H down gradients powers ATP formation via the enzyme ATP synthase • Produces water as a by product • •

16. Briefly describe the process of electron transport phosphorylation by stating what reactants are needed and what the products are. State how many ATP molecules are produced through operation of the transport system. Reactants: NADH, FADH2, ADP, Pi (inorganic phosphate) and oxygen The reactants, NADH and FADH2, transfer high energy hydrogen electrons to the inter membrane electron transport molecules and the hydrogen ions are shuttled across this membrane to set up a H+ gradient. The energy of the gradiant is coupled with ATP formation with the help of ATP synthase. Thus the products below are formed. Including 32 ATP molecules. Oxygen is the ultimate receiver of the spend electrons and hydrogen ions. As oxygen is reduced, water is formed.

Products: NAD+, FAD+2, ATP, and water

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17. List some places where there is very little oxygen present and where anaerobic organisms might be found.

The bottom of ponds, swamps, sewers, and hydrothermal vents. Also in soils and canned foods that have not been properly sterilized.

18. Describe what happens to pyruvate in anaerobic organisms. Then explain the necessity for pyruvate to be converted to a fermentative product.

Pyruvate is usually converted ohe of the following: ethanol or lactic acid. By reducing pyruvate, the high energy hydrogen produced in glycolysis is rendered harmless.

19. You have been fasting for three days, drinking only water and eating no solid food. Tell which stored molecules your body is using to provide energy, and describe how that is occurring.

Fats (triglycerides). The triglycerides are cleaved into glycerol and fatty acids. The glycerol (3C) is converted to PGAL, where it enters glycolysis. The fatty acid chain (18 C) is degraded into acetyls (2C). These 2C molecules combine with CoA and enter the Kreb’s cycle ultimately produces ATP, CO2 and H2O via the completion of ETP within the mitochondria. 20. After reading "Perspective on Life" in the main text, outline the supposed evolutionary sequence of energyextraction processes.

Anaerobic consumption of accumulated oceanic organics (energy source prior to the evolution of photosynthesis) via glycolysis. Evolution of cyclic photosynthesis (PS 1) and accumulation of atmospheric oxygen. Non-cyclic photosynthesis evolves later. . Evolution of aerobic respiration in the presence of oxygen becomes the dominate form of respiration. For the most part, the modern biosphere is driven by solar energy. This energy is used to keep cells highly organized and reproducing (DNA  next generation of cells and so on…

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21. Closely scrutinize the diagram of the carbon cycle in the Commentary; be able to reproduce the cycle from memory.

Refer to slide 48, “The Processes are Linked”, of the PPP for this chapter for the complete diagram or your text.

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