Cellular Respiration Releases Energy from Organic Compounds The

Cellular Respiration Releases Energy from Organic Compounds

The Process of Cellular Respiration o Three Pathways for Energy Release n Aerobic Cellular Respiration p Requires oxygen (oxicconditions)

Releasing energy without oxygen n Anaerobic Cellular Respiration p Occurs in the absence of oxygen (anoxic conditions) – oxygen may be lethal to the organism n Fermentation p An anaerobic process

Aerobic Cellular Respiration o Oxidation reaction n n Electrons move from high-energy molecules (eg. Glucose) to oxygen Main process for releasing energy (ATP) in most eukaryotic cells

Aerobic Cellular Respiration o Key Events n n n Glycolysis Krebs Cycle Electron Transport System

Outside the Mitochondria: Glycolysis o Occurs in all living cells o Can proceed anaerobically o Goal: split glucose (6 -C) into 2 pyruvate molecules (3 -C)

Steps of Glycolysis o Energy (2 ATP) is added to glucose to start reactions o 2 intermediate 3 -C molecules are formed o 4 molecules of ATP are synthesized, and NAD+ is reduced to NADH o 2 molecules of pyruvate are formed o NET GAIN: 2 ATP and 2 pyruvate molecules

Glycolysis overview 2 ATP Glucose (6 -C) 2 ADP Intermediate 3 -C molecule (PGAL) 4 ADP 4 ATP Pyruvate (3 -C)

Krebs Cycle Preparation o Pyruvate breaks down into CO 2 and a 2 carbon group (acetyl) which bonds to a coenzyme acetyl Co. A o NAD+ is reduced to NADH

The Krebs Cycle o It is a cycle because one of the products becomes a reactant o Cycle occurs twice for each molecule of glucose processed o During one cycle: n n n 3 NADHs and 1 FADH 2 are formed 1 ATP is formed 2 CO 2 molecules are produced and released as waste

Electron Transport o Most ATP molecules in cellular respiration are produced during electron transport o Very similar to electron transport in chloroplasts

Oxygen in the e- transport chain o In this case, oxygen is the final electron acceptor, and also picks up excess H+ n Creates water molecules

Role of Oxygen in Aerobic Cellular Respiration o Oxygen picks up the electron from the last set of reactions in electron transport o So why is it so important? ? ? n If it did not pick up the last electron, the entire process would become backed up – electrons from previous steps would not be passed on. o Glycolysis would be the only part of aerobic cellular respiration that could proceed doesn’t produce enough ATP for life functions of most Ekaryotic cells

Anaerobic Cellular Respiration Uses a Different Final Electron Acceptor o Occurs in some prokaryotic cells o Uses another type of electron transport system

Anaerobic Respiration o Not as efficient (less ATP synthesized) o Oxygen not available, so it uses sulfate, nitrate, or carbon dioxide as the final electron acceptor o Byproducts: S 8, N 2, nitrite, or methane

Fermentation o Occurs in cytoplasm o A pathway including glycolysis and the oxidation of NADH NAD+ by reducing pyruvate

Fermentation o Inefficient – only produces ATP in glycolysis o Many types of fermentation, including: n Lactate Fermentation n Ethanol Fermentation

Lactate Fermentation o Pyruvate is converted to lactate (lactic acid) o Eg) muscle soreness during a workout n n n Rate of glycolysis exceeds oxygen supply Lactic acid is temporarily stored in muscles, causing cramping After exercise, lactic acid is converted back to pyruvate as oxygen supply is replenished

Ethanol Fermentation o Yeasts and other organisms o Convert pyruvate to ethanol and carbon dioxide o Used commercially to make bread, wine, beer, champagne, mead, cider… o Ethanol is released as a waste product

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