Warm Up - 10/4

Explain the process of aerobic cellular respiration.

Aerobic cellular respiration begins with glycolysis, the conversion of a molecule of glucose into two pyruvate molecules and two ATP molecules.  The first step of glycolysis is phosphorylation, where hexokinase and then phosphofructokinase add two phosphates to the glucose molecule, creating a hexose biphosphate.  The second step of glycolysis is lysis, the splitting of hexose biphosphate into two 3-carbon sugars by the enzyme aldolase.  These 3-carbon sugars are called G3P, PGAL, or triose phosphate.  The third step of glycolysis is oxidation where each G3P molecule loses two atoms of hydrogen by converting NAD+ into NADH + H+.  The creation of NADH releases energy to add a phosphate group to both G3Ps.  The resulting 3-carbon molecules with extra phosphate are called PGA.  In the fourth step of glycolysis, ATP formation, ADP undergoes substrate-level phosphorylation, producing ATP.  The remaining carbon and phosphate molecule is turned into pyruvate.

Fatty acids can also be used to bypass glycolysis.  Since fatty acids are a long chain of carbon molecules, coenzyme CoA oxidizes this chain and breaks it down, making Acetyl CoA with two carbons.

After glycolysis, the link reaction occurs.  Pyruvate is decarboxylated to form an acetyl group (2C) and CO2 is released.  Then the pyruvate is oxidized and NAD+ accepts a hydrogen to form NADH + H+.  The acetyl group combines with a coenzyme (CoA) to form Acetyl CoA, which enters the Krebs cycle.

In the Krebs Cycle, Acetyl CoA combines the acetyl group (2C) with oxaloacetate (4C), forming citrate (6C).  Citrate undergoes oxidative decarboxylation, converting NAD+ into NADH + H+ and producing CO2.  This forms a 5 carbon molecule, which undergoes oxidative decarboxylation again, making a 4 carbon molecule.  Substrate level phosphorylation occurs, adding a phosphate to ADP to create ATP.  FAD2 is converted into FADH2 and NAD+ is converted into NADH + H+.  After these reactions, the 4 carbon molecule is converted into oxaloacetate, which is used in the next turn of the Krebs Cycle.  The products of the Krebs Cycle are used to power the Electron Transport Chain.