The Citric Acid Cycle
The citric acid cycle is the next step in cellular respiration. The two pyruvates produced in glycolysis enter the mitochondria through transport proteins and get converted into acetyl CoA. This is the preparation step for the actual citric acid cycle:
1 pyruvate, 1 NAD+, and 1 Coenzyme A -----> 1 acetyl CoA, 1 NADH, 1 H+, and 1 CO2.
Note this is the first step in cellular respiration where carbon dioxide is produced. Also, since each molecule of glucose produces two pyruvates, we can double the above reaction to get:
2 pyruvate, 2 NAD+, and 2 Coenzyme A -----> 2 acetyl CoA, 2 NADH, 2 H+, and 2 CO2.
Now, let's get to the actual citric acid cycle. This is another complex process that you do not have to remember. However, you need to know what comes in and what goes out.
1 acetyl CoA, 3 NAD+, 1 inorganic phosphate, 1 ADP, 1 FAD, H2O -----> Coenzyme A, 2 CO2, 3 NADH, 1 FADH2, 3 H+, and 1 ATP
Double that (because there are two acetyl CoA's produced for every glucose) and we get:
2 acetyl CoA, 6 NAD+, 2 inorganic phosphate, 2 ADP, 2 FAD, 2H2O -----> 2 Coenzyme A, 4 CO2, 6 NADH, 2 FADH2, 6 H+, and 2 ATP
The key products here are 6 NADH electron carriers, 2 FADH2 electron carriers, and 2 ATP.
If we add the 2 NADH formed in the preparation step we get 8 NADH, 2 FADH2, and 2 ATP.
If we add the 2 NADH and 2 ATP from glycolysis, our current subtotal is 10 NADH, 2 FADH2, and 4 ATP. However, right now most of the energy is harnessed within the 12 electron carriers. (Note that the 2 NADH from glycolysis may be shuttled into the mitochondrion as either NADH or FADH2, so technically we can also have 8 NADH, 4 FADH2, and 4 ATP.) The energy stored in NADH and FADH2 will soon be released in oxidative phosphorylation.
1 pyruvate, 1 NAD+, and 1 Coenzyme A -----> 1 acetyl CoA, 1 NADH, 1 H+, and 1 CO2.
Note this is the first step in cellular respiration where carbon dioxide is produced. Also, since each molecule of glucose produces two pyruvates, we can double the above reaction to get:
2 pyruvate, 2 NAD+, and 2 Coenzyme A -----> 2 acetyl CoA, 2 NADH, 2 H+, and 2 CO2.
Now, let's get to the actual citric acid cycle. This is another complex process that you do not have to remember. However, you need to know what comes in and what goes out.
1 acetyl CoA, 3 NAD+, 1 inorganic phosphate, 1 ADP, 1 FAD, H2O -----> Coenzyme A, 2 CO2, 3 NADH, 1 FADH2, 3 H+, and 1 ATP
Double that (because there are two acetyl CoA's produced for every glucose) and we get:
2 acetyl CoA, 6 NAD+, 2 inorganic phosphate, 2 ADP, 2 FAD, 2H2O -----> 2 Coenzyme A, 4 CO2, 6 NADH, 2 FADH2, 6 H+, and 2 ATP
The key products here are 6 NADH electron carriers, 2 FADH2 electron carriers, and 2 ATP.
If we add the 2 NADH formed in the preparation step we get 8 NADH, 2 FADH2, and 2 ATP.
If we add the 2 NADH and 2 ATP from glycolysis, our current subtotal is 10 NADH, 2 FADH2, and 4 ATP. However, right now most of the energy is harnessed within the 12 electron carriers. (Note that the 2 NADH from glycolysis may be shuttled into the mitochondrion as either NADH or FADH2, so technically we can also have 8 NADH, 4 FADH2, and 4 ATP.) The energy stored in NADH and FADH2 will soon be released in oxidative phosphorylation.