Cellular Respiration Questions
Aerobic pathways require oxygen, while anaerobic pathways don't.
Anaerobic pathways only require the process of glycolysis to produce energy. Anaerobic pathways are found outside the mitochondria within the cytoplasm of the cell, with a low efficiency of 4%. These pathways require glucose, ATP, adolase, fructokinase, dehydrogenase, and NAD+. Out of one glucose molecule, major products include two net ATP, two NADH, and two pyruvate molecules. The latter can be produced without the use of an aerobic process, such as the Krebs cycle. The two pyruvates eventually get produced into either the painful lactic acid, or ethyl alcohol (fermentation).
Aerobic pathways require oxygen to produce energy. Aerobic pathways can be found inside the mitochondria, and are 40% efficient, much more efficient than anaerobic pathways. Aerobic pathways include the Krebs cycle and the election transport chain. The input of aerobic pathways include glucose, oxygen, NAD+, and the same enzymes that anaerobic pathways need. The difference is that aerobic pathways can produce a max of 36 ATP, which is way more efficient that anaerobic pathways. Aerobic pathways also produce FADH2, which is NADH's “backup”. They also produce CO2, which is expelled from our body by gas respiration in our lungs. It is clear why our bodies choose aerobic pathways over anaerobic pathways.
The general redox reaction is XH2 + NAD+ → X + NADH + H+ . The purpose of transferring electrons is to produce NADH, which will be used in the electron transport chain to ship hydrogen ions onto the other side of the cristae membrane, to make a concentration gradient that will eventually be used to produce ATP. These redox reactions occur in almost all steps of cellular respiration, including glycolysis, “chemical grooming”, and the Krebs cycle. Without NADH produced, the electron transport chain couldn't function, which would jeopardize aerobic respiration entirely. This transfer of electrons is a biological necessity.
Chemiosmosis is the process of producing ATP in the electron transport chain, by runnning hydrogen ions across ATP synthase, that spins and cranks out ATP molecules from ADPs and phosphate groups. Chemiosmosis takes effect inside the mitochondria. Chemiosmosis is the long-term investment, almost like a retirement fund. ATP isn't automatically produced in this process, as it is in substrate level phosphorylation (SLP). Instead, when the time comes, a massive amount of ATPs are produced by this process. The major advantage of chemiosmosis is that more ATPs are produced per glucose molecule than SLP. The downfall of chemiosmosis is that it isn't as rapid of a process as is SLP, and that oxygen is required for it to function.
SLP is the process of producing ATP anaerobically without the use of the electron transport chain, such as the ATP produced in glycolysis and the citric acid cycle. SLP is a short-term investment, like a checking account. It takes place outside the mitochondria, in the cytoplasm. The pros of SLP include the fact that ATP is easily, rapidly produced, and that no oxygen is required for SLP to function. The cons include the fact that the level of ATP produced by SLP is substantially lower than chemiosmosis. From a single glucose molecule, two net ATPs in glycolysis and two ATPs in the citric acid cycle are produced, making a total of four ATP molecules. This amount of ATPs is not enough to meet the energy needs of most organisms. As said before, this is why our bodies mostly use aerobic pathways, and not anaerobic pathways. Efficiency is key!