"SUGAR, GIVE ME SOME ENERGY"...
The second metabolic pathway in order of dominance of energy production is anaerobic glycolysis. This metabolic pathway is dedicated to the breakdown (catabolism) of carbohydrates (carbs). First, notice that I wrote the breakdown of carbs, and not the breakdown of sugar/s.
This point will become important to understand and notice later on, since every sugar is a carb, yet not every carb is considered a sugar. Thus, the catabolism of a carb even though it is not a sugar will count as a glycolytic process. In general, simple carbs are smaller molecules that commonly include glucose, fructose and galactose. More complex carbs tend to be bigger in size and commonly include oligosaccharides of milk, the cellulose of plant cell walls, and storage forms such as starch and glycogen.
Advertisement
In this post dedicated to glycolysis, we will focus on glycogen and glucose. Glycogen is the storage form for glucose that is not immediately used or not used within a short term. Glycogen molecules tend to vary in size, and can contain between 1,000 - 50,000 sub-units of glucose molecules. In other words, simplified, glycogen resembles a lengthy chain of glucose (similar to a beads necklace, where each bead represents a glucose molecule stored as part of the glycogen molecule.
The average and untrained person has about 30 grams of free glucose that is not stored, about 70 grams of glucose within the liver organ, and about 400 grams of glycogen within the muscles as backup carb storage. A high level competitive athlete tends to have 100 grams more compared to the untrained person. Any carbs beyond these amounts will be stored as fat, and some will help create muscle mass.
Glycolysis of glucose includes ten reactions, mediated by enzymes, two reactions of which act as chemical milestones that ensure that the process proceeds in one direction. Since these two reactions are not reversible, the process goes from whole molecule to catabolized molecule. Glucose is made of two molecules of pyruvate and four hydrogen atoms.
During glycolysis in the cytoplasm of the cell, glucose is split into two molecules of pyruvate and four hydrogen atoms. If the cell is experiencing a lack of oxygen (anaerobic conditions), each pyruvate molecule binds two of the hydrogen atoms to create lactic acid, mediated by anaerobic enzymes within the cell. Thus, due to the lack of sufficient oxygen within the cells, acidity goes up by two acid molecules per pyruvate or in other words, two acid molecules per glucose catabolized anaerobically (anaerobic glycolysis).
At the end of anaerobic glycolysis, the cell receives four molecules of ATP as a result, in addition to the acid molecules created. Yet, these four ATP molecules are not all "profit" or "net profit" since they do not account for the energy costs of the glycolysis process itself. The cost of catabolizing two different glucose molecules is not necessarily the same. If the glucose has never been stored before as part of a glycogen molecule, it will cost double the cost to breakdown a glucose molecule that has been stored as glycogen.
For every glycolysis of one molecule of glucose that was not stored before ("free" glucose) we invest two molecules of ATP, while we only invest one molecule of ATP if the glucose was stored before as part of a glycogen molecule. Thus, in the case of free glucose (never stored before) the calculation is four ATP received, two ATP invested, and two ATP left as net profit at the cell's disposal. In the case of glucose stored before as part of a glycogen molecule, the calculation is four ATP received, one ATP invested, and three ATP left as net profit at the cell's disposal.
The anaerobic glycolytic metabolic pathway occurs completely in the cytoplasm of the cell from start to end. It is second fastest in its energy creation, and yields the second most energy in absolute terms per one cycle of the process. This metabolic pathway is second in the order of dominancy as related to energy production since the phosphagen is faster, and the aerobic metabolic pathway is slower. Thus, it ends up serving as a metabolic bridge between the point in which creatine phosphate can no longer be dominant in energy production and the point in which there is enough oxygen within the cell to create energy aerobically to a dominant extent.
Advertisement
Combining the function thus far of our two anaerobic metabolic pathways, the phosphagen and anaerobic glycolysis pathways, they are the main energy suppliers for activities of up to 120 seconds or so (two minutes). A person that is more aerobically fit, shortens this period of time, and begins to create aerobic energy earlier, reducing the amount of acids created in the meanwhile. Since anaerobic glycolysis increase the acidity of the cell, and acidity negatively influences function, the cells aspire to utilize anaerobic glycolysis as little as possible, if at all possible.
Comments