Chapter 9 - Cellular Respiration 

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• The glucose molecule is oxidized (loses hydrogen atoms and electrons) during glycolysis, and each NAD+ molecule is reduced (gains a hydrogen atom and electrons) to NADH.
  • Keep in mind that everytime one molecule is oxidized, another must be reduced.
• Carbon-containing compounds are oxidized during cellular respiration, whereas the electron carriers NAD+ and FAD+ are reduced.
  • In the early stages of glycolysis, two molecules of ATP are required.
  • However, glycolysis produces four molecules of ATP, resulting in a net gain of two ATP molecules.
  • The six-carbon glucose molecule is broken into two three-carbon pyruvate molecules at the end of glycolysis.
• Glycolysis is a multistep process involving several enzyme-catalyzed stages and intermediates.
  • Focus on where each step in cellular respiration happens and what the inputs and outputs are for each process when studying for the AP Biology test.
  • The mitochondria are responsible for the next stage in cellular respiration.
  • To enter the cell, the three-carbon pyruvate molecule must be changed.
• ^^Four molecules of ATP were produced as a result of substrate-level phosphorylation (two in glycolysis and two in the Krebs cycle).^^
  • Twelve high-energy electron carriers (10 NADH and two FADH2) have been produced and will move on to the next stage of cellular respiration: oxidative phosphorylation.
  • The electron transport chain (ETC) and chemiosmosis, which both occur on the inner membrane of the mitochondria, are both involved in oxidative phosphorylation.
  • The vast majority of ATP generated in cellular respiration is produced by oxidative phosphorylation.
• Electron carriers (NADH and FADH2) created during glycolysis, pyruvate oxidation, and the Krebs cycle carry electrons to the inner mitochondrial membrane's electron transport chain.
  • The potential energy of electrons lowers as they pass along the electron transport chain, and energy is liberated.
  • This energy is utilized to push protons (H+) out of the matrix and into the mitochondrial intermembrane space, resulting in a proton gradient.
  • Proton concentrations in the intermembranous region can be 1,000 times higher than in the matrix!
• Molecular oxygen (O2) interacts with four protons (H+) and four electrons (e–) at the end of the electron transport chain to generate two water molecules.
  • As a result, during cellular respiration, oxygen serves as the ultimate, or terminal, electron acceptor.
  • The electron transport chain's proton gradient is employed to drive ATP production.
  • ^^Chemiosmosis is the process of using a proton gradient to stimulate the synthesis of ATP.^^
  • ^^ATP is an enzyme.^^
• Some membranes, for example, may be "leaky," allowing protons to enter the inner membrane of the mitochondria without passing through ATP synthase.
  • As a result, the actual results from this technique may vary.
  • NADH is oxidized (at the electron transport chain) to NAD+ during oxidative phosphorylation, which can subsequently be utilised in glycolysis.
• However, oxidative phosphorylation cannot proceed in the absence of oxygen.
  • (Recall that oxygen is the ETC's last electron acceptor.)
  • Without oxygen, the ETC is unable to discharge its low-energy electrons from the final carrier, causing the chain to get clogged and the system to shut down.)
  • Cells ferment under anaerobic environments to renew the NAD+ required to keep the glycolysis process going.
  • If a cell ran out of NAD+, it would die.

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