Atp Production Essay, Research Paper
Metabolism, which encompasses glycolysis, the Kreb s cycle, and the electron transport system, occurs in the mitochondria of cells. The mitochondria consist of a double membrane and an inner compartmentalization called the matrix. Each of the processes of metabolism occurs in specific locations in and around the mitochondria. The process of glycolysis occurs in the cytoplasm just outside the outer membrane of the mitochondria. The Kreb s cycle occurs within the matrix and the electron transport system in the convoluted inner membrane called the cristae. When considering the location and process of the electron transport system, you would observe that all of the components (enzymes/proteins) necessary for this process are contained with the cristae membrane.
When trying to define a starting point concerning the production of ATP, you could consider glycolysis. Glycolysis basically provides the components which will ultimately drive the process involved in ATP production. Glycolysis yields two three-carbon compounds called pyruvate from one glucose molecule. Pyruvate plays a crucial role in the Kreb s cycle. Glycolysis also yields a number of Hydrogen ions and electrons, which will be used in the electron transport system. Glycolysis also yields a net production of two ATP.
Before the pyruvate molecules can be used in the Kreb cycle, they must be converted to Acetyl CoEnzyme A (Acetyl CoA). This occurs during the intermediate step. CoEnzyme A is introduced to the two pyruvate molecules from glycolysis. An NAD+ picks up a hydrogen ion from both the CoEnzyme A and the pyruvate. CoEnzyme A reacts with the pyruvate releasing carbon dioxide and yields Acetyl CoA. Acetyl CoA will now enter the Kreb s cycle within the matrix.
Acetyl CoA starts the Kreb s cycle by catalyzing a reaction between the Acetyl portion of Acetyl CoA and oxaloacetate. This yields a six-carbon compound called citrate or citric acid. Next, a water molecule is released from the citrate causing a change in the structure. The water is then added back on to the citrate, forming an isomer of citrate called isocitrate. A molecule of CO2 is released and transferred to the lungs for export, while NAD+ picks up the hydrogen ions and the electrons and transports them to the electron transport system. The enzyme alpha-ketoglutarate now enters the cycle causing the last of the two CO2 molecules removed in the Kreb s cycle. NAD+ again picks up any hydrogen ions and electrons and transports them to the ETS. The new product, succinyl, is picked up by CoEnzyme A while an inorganic phosphate is phosphorylated by GDP yielding a GTP. At this point, an ADP will act upon the GTP, and pick up the inorganic phosphate that was phosphorylated. This yields an ATP and returns the GTP to a GDP. The remaining product is called succinate. FAD acts upon the succinate molecule and removes two hydrogen ions and transports them to the ETS. This yields fumerate. Water is added to the fumerate to form malate. The last of the three NAD+ removes two hydrogen ions forming oxaloacetate which is ready to be acted upon by another acetyl CoA. This process describes one turn of the Kreb s cycle. The Kreb s cycle consists of this process twice through. The Kreb s cycle will yield two ATP s and six NADH + H+ from one molecule of glucose.
The final and most productive step in the production of ATP, is the electron transport system. Again, this process takes place in the cristae or inner-membrane. The elcetron transport system begins with and NADH + H+ derived from either the Kreb s cycle or glycolysis. The first protein in the electron transport chain (ETS), flavo protein, releases the two hydrogen ions into the intermembrane the space between the outer membrane and the cristae. At the same time, it transfers the two electrons to the next protein in the chain. The second protein, iron sulfur protein, passes the two electrons to the third, quinone enzyme. At this point, an FADH2 , derived from the Kreb s cycle, is acted upon by the Q enzyme. The two hydrogen ions are released into the intermembreane. Q enzyme also transfers the elcetrons along the chain. It sends one electron to one citochrome b , and the other electron to another citochrome b. The citochrome b offsets these two electrons so as to allow one to follow the other to the next citochrome, citochrome C1 . C1 transfers one electron at a time to citochrome C, then C transfers to A, and then to A3 . A3 releases the electrons back into the matrix to the electron acceptor oxygen. With the accumulation of hydrogen ions in the intermembrane, there exists/forms and electrochemical gradient. With the help of a chemiosmotic pump, this electrochemical gradient moves back towards equilibrium. Kinase, located in the cristae, transfers two hydrogen ions across the cristae into the matrix. The energy derived from these protons phosphorylates an inorganic phosphate to an ADP in the matrix, forming an ATP. The hydrogen ions react with the oxygen that accepted the released electrons and forms water. The ETS will produce 34 ATP s in this manner from just one glucose molecule that has passed through glycolysis, the intermediate step, and the Kreb s cycle. Thus, with all of the processes combine, 38 ATP s are produced from one glucose molecule.