The Krebs Cycle and Role of Amino Acids

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Aerobic respiration is used by many organisms in the animal kingdom, including humans like you and me. It is a metabolic reaction that requires oxygen to produce ATP or energy. The equation for aerobic respiration is C6H12O6 + 6 O2 = 6 CO2 + 12 H2O + 38 ATP (engergy).

In simple terms it means organisms take in food and water, and put out CO2, water, and energy.
In this process, there are four steps, including glycolysis, formation of acetyl CoA, the Krebs cycle, and theelectron transport chain. We will primarily discuss glycolysis, the Krebs cycle, amino acids needed, and the electron transport chain.

Before the Krebs cycle begins, glucose needs to be broken down into the proper components before they can enter the cycle. First it is broken down into 2 3-carbon molecules of pyruvate in the cytoplasm of the cell.

This is known as glycolysis, which consumes 2 ATP, and produces 4 molecules of ATP, and  two molecules of NADH. Some organisms can survive on glycolysis alone for their energy,  while others continue the process to get more ATP. After the glucose is turned to pyruvate, it gets oxidized to carbon dioxide, and a 2-carbon acetyl group. It is then bound to coenzyme A, and shuttled into the mitochondria in the cell, while carbon dioxide is released as a waste product.

The next stage in energy production is the Krebs cycle, also known as the citric acid or Calvin cycle. Each of the acetyl groups produced from the original glucose molecule gets bonded to a molecule of oxaloacetate to form citrate or citric acid.

This is where the name of the cycle comes from. These are the Krebs cycle’s amino
acids needed to start the cycle. These two citric acid molecules get slowly oxidized  and hydrogen ions become bound to NAD form NADH and FAD from FADH2.

When the last carbon atom is released in the form of CO2, oxaloacetate is produced. This process forms 2 ATP molecules for every glucose that enters the cell.

After the Krebs cycle, the electrons removed from this process follow many cytochromes on
the mitochondrial membrane in eukaryotic cells, and the plasma membrane of bacteria.

Here, hydrogen ions get pumped across the inner membrane of the mitochondria and flow through ATP synthase enzyme molecules. As the electrons pass through the electron transport chain, they fall to lower and lower energy states.

This energy that is released is used to drive H+ ions across the membrane, which in turn generates a transmembrane gradient of H+ ions. These hydrogen ions serve as a battery like source of energy to drive the phosphorylation of ADP to make 34 ATP per molecule of glucose.

Now you should be pretty familiar with glycolysis, the Krebs cycle, amino acids needed, and the electron transport chain, making the understanding of aerobic respiration, a breeze!