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#1. During aerobic cellular respiration, stored energy from glucose is extracted and stored in
the high-energy bonds of ATP. Known as the “energy currency of life,” ATP can store and
transport the energy required by all metabolic functions of living cells. Due to aerobic respiration,
energy is released from chemical bonds and used for “phosphorylation” of ATP. By adding a
phosphate ADP becomes ATP. Aerobic cellular respiration encompasses: Glycolysis, Transition
Reaction, Kreb’s Cycle, and Electron Transport System, with Chemiosmosis. Oxidizing 1
molecule of glucose nets a total of 38 ATPs. The overall equation for aerobic cellular respiration
is: carbohydrate + oxygen yield carbon dioxide, water, and ATP. During these reactions, oxygen
is typically consumed, but the process may be anaerobic or aerobic, depending upon availability.
#2. Glycolysis literally means ‘splitting sugars.’ Cellular respiration starts with glycolysis for
ALL living organisms (aerobes and anaerobes), in the cytosol. Two ATPs initiate the process.
Glucose (a six-carbon sugar) partially oxidizes and breaks down into 2 three-carbon molecules
called pyruvate. As glucose breaks down, hydrogen atoms will be used to reduce the coenzyme
NAD+ to NADH. Glucose’s chemical breakdown produces a total of 4 ATP, but the net gain will
only be 2 ATP. The reactants for glycolysis include: glucosease activation energy, 4ADP and 4P,
enzymes, and 2 NAD+. The products include: 2 pyruvates, 2 ATP net, and 2 NADH.
Without oxygen, many cells may carry out fermentation. This step also occurs in the cytosol, but
only allows for small amounts of energy production. Pyruvate, a product of glycolysis, can be
used in fermentation to produce 2 ethanol and 2CO2 (plant and yeast cells) or 2 lactic acid
molecules (animal and bacterial cells). Beginning with 1 molecule of glucose, the net yield from
fermentation is 2 ATP that originated in glycolysis. Once fermentation is completed, anaerobic
respiration is done. The reactants for fermentation include: 2 pyruvate and 2 NADH. The
products include: 2 lactic acid or 2 ethanol and 2 CO2, 2 NAD+, and 2H.
Transition Reaction: This is the secondary pathway in aerobic cellular respiration. Pyruvate
molecules enter the mitochondrion’s matrix and are converted into 2 acetyl CoA molecules. For
each pyruvate, 1 CO2 is released and 2 NADH are formed. The resulting acetyl-CoA are 2carbon molecules with coenzyme A temporarily attached. Now acetyl-CoA molecules can enter
the next respiration phase, Kreb’s Cycle. During Transition Reaction, no ATP is produced. This is
a conversion stage, and also the first time we encounter waste (CO2). (At the end of transition
reaction, we have 2 acetyl COA, 2NADH, and 2 CO2 products.)
Krebs Cycle: This is the third pathway in aerobic cellular respiration, and it occurs in the
mitochondrion’s matrix. Acetyl-CoA enzymes enter this step of respiration. It is a cyclical
process of oxidation and decarboxylation reactions resulting in the net formation of 6 NADH and
2 FADH2, and 4 CO2. During the Kreb’s Cycle, 2 ATP molecules are formed.
The Electron Transport Chain: This is the last pathway for aerobic cellular respiration. It is a
system of molecules imbedded in the mitochondrion’s inner membrane, which accept and lose
electrons, passing the electrons from one molecule to the next. In aerobic respiration at the end of
electron transport, the electrons combine with oxygen and hydrogen ions to form water
molecules. Electron transport is responsible for pumping hydrogen ions into the cristae, enabling
the process of chemiosmosis to occur. A total of 34 ATP’s are produced here.