biology notes Essay

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Bio101 Lecture 15: Cellular Respiration. Part1: Glycolysis and Fermentation I-­‐Cellular Respiration CR A-­‐Definitions CR: process by which organisms breakdown and extract energy from nutrients (carbs, glucose) produced by photosynthesizers. Slide 3 CR can take place in presence of Oxygen, aerobic respiration, or absence of Oxygen, anaerobic respiration, also called fermentation. Slide 4. In anaerobic conditions, Fermentation processes Sugars from food into lactic acids, or into carbon dioxide CO2 and alcohols. Slide 4 In aerobic conditions, CR processes Sugars from food into CO2, water and Energy (ATP). Slide 4. Here, CR is essentially a redox reaction where Glucose is oxidized into CO2 (Glucose loses H+ and electrons e-­‐), and O2 reduced into Water (Oxygen gains H+ and electrons e-­‐). Slides 4, 5. It’s also a catabolic/exergonic reaction that releases energy. Slide 6

Recall: this reaction obeys the second law of thermodynamics (heat, entropy) as some energy is lost as heat. Why is glucose a high-­‐energy molecule? Recall that in atoms, lower shells have low energy and higher shells have high energy.

Glucose is a high-­‐energy molecule because the Carbon atoms allow their electrons wander freely around the outermost shells where they acquire high energy. Glucose is instable, organized, less entropic and tends to decompose into CO2 and Water H2O.



CO2 and Water H2O are low-­‐energy molecules because Oxygen retains the electrons at lower shell, which have less energy. Oxygen has a high affinity to electrons. The word oxidation comes from the fact that Oxygen “steals” electrons from other atoms. CO2 and Water H2O are stable, more entropic, less organized. Because glucose is a high-­‐energy molecule, it would ignite quickly after encounter with Oxygen, and its high energy will be lost. Analogy: paper is made of cellulose (polymer of glucose). Burning a piece of paper releases quickly energy (heat), CO2 and Water H2O (vapor). Slide 7 Burning glucose in cells is no a quick process. It takes place in steps called metabolic pathways. The pathways of CR allow energy in glucose to be released slowly, in several steps so that ATP can be produced gradually and in abundance. Under perfect conditions with no loss of energy as heat one molecule of glucose would yield 96 ATP molecules (100%). In CR, because of the heat loss and second…