Bio1151 Chapter 9 Cellular Respiration
  1. Living organisms require         to perform cellular work. Energy flows into most ecosystems as           and leaves as       .

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      Energy flows into an ecosystem as sunlight and ultimately leaves as heat, while the chemical elements essential to life are recycled.


      At the cell level, energy from sunlight is stored in organic compounds by photosynthesis in chloroplasts. A byproduct of this process is oxygen. The organic compounds and oxygen are used by mitochondria to produce ATP for work in a process called cellular respiration. Byproducts of respiration are water and carbon dioxide, which are used as raw material for photosynthesis. Heat is released into the environment in this cycle.
     
     
     
     
  2. Cellular              is a catabolic pathway that consumes         and organic molecules and yields the energy molecule      by the transfer of            .
     
     
     
     
  3. Electron transfer occurs through chemical reactions called        reactions. Molecules such as NAD+ and FAD act as electron receptors in this pathway.

      In a redox reaction, one substance loses electrons (oxidation) and energy while another gains electrons (reduction) and energy.


      Nicotinamide Adenine Dinucleotide Two electrons and one proton (H^+) from an organic molecule such as glucose is transferred to NAD^+ which is reduced the to NADH. The NADH stores energy that can be tapped to make ATP when the electrons complete their fall down an energy gradient to oxygen.
     
     
     
     
  4. In cellular respiration,          is oxidized and         is reduced, in a series of steps called the           transport chain (ETC) to form      .

      The uncontrolled exergonic reaction of hydrogen with oxygen to form water releases a large amount of energy: an explosion. In cellular respiration, an electron transport chain breaks the fall of electrons into a series of smaller steps and stores some of the energy to make ATP, the rest of the energy is released as heat.
     
     
     
     
  5. Cellular respiration comprises three metabolic stages:             ,         acid cycle, and            phosphorylation.

      An overview of cellular respiration. During glycolysis, a glucose molecule is broken into 2 molecules of pyruvate in the cytosol. The pyruvate enters the citric acid cycle in the mitochondrion; these 2 steps produce a few molecules of ATP by substrate-level phosphorylation NADH and FADH[2] transfer electrons to the ETC, where oxidative phosphorylation produces much more ATP by chemiosmosis. 3
     
     
     
     
    •             occurs in the          to produce two molecules of      from the metabolism of one          molecule.

        Glycolysis ("splitting of sugar") occurs in the cytosol and breaks down one glucose molecule into two molecules of pyruvate, yielding a net gain of 2 ATP amd 2 NADH molecules.
       
       
       
       
    • The           is converted to         CoA, which enters the         acid cycle in the matrix of the mitochondrion.

        Several enzymes catalyze the conversion of 3-carbon pyruvate to 2-carbon acetyl CoA. The acetyl CoA enters the citric acid cycle, while CO[2] diffuses out of the cell.
       
       
       
       
    • During            phosphorylation, NADH and FADH2 donate            to the ETC to produce about 32 to 34 molecules of ATP.


      As high-energy electrons move along a series of protein complexes, they pump hydrogen ions (protons) across the membrane, producing a gradient of H^+. The protons diffuse back (chemiosmosis) through the enzyme ATP synthase to form ATP. This process requires oxygen (the final electron acceptor) and releases water.


      ATP yield per molecule of glucose at each stage of cellular respiration. Since oxygen is required to complete the citric acid cycle and oxidative phosphorylation, these two processes are known as aerobic respiration.
     
     
     
     
    Review: Cellular Respiration
     
     
     
     
  6. In            conditions, glycolysis is followed by               , which does not produce      , but regenerates NAD+, and allows glyocolysis to continue generating      .

      Fermentation. In the absence of oxygen, some cells undergo fermentation instead of aerobic respiration. Pyruvate serves as an electron acceptor for oxidizing NADH back to NAD^+, which is reused in glycolysis. Two end products formed from fermentation are ethanol with the release of CO[2] and lactic acid. Note that fermentation. itself yields no ATP molecules; it serves to recycle NADH back to NAD^+.
     
     
     
     
  7. Other organic molecules such as           and       can also enter cellular respiration via different            pathways.

      The catabolism of various molecules from food. Carbohydrates, fats, and proteins can all be used as fuel for cellular respiration. Monomers of these molecules enter glycolysis or the citric acid cycle at various points.