{"id":2295,"date":"2016-05-20T21:33:34","date_gmt":"2016-05-20T21:33:34","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/biologyxwaymakerxmaster\/?post_type=chapter&p=2295"},"modified":"2024-04-26T22:24:22","modified_gmt":"2024-04-26T22:24:22","slug":"cellular-respiration","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-biology1\/chapter\/cellular-respiration\/","title":{"raw":"Cellular Respiration","rendered":"Cellular Respiration"},"content":{"raw":"Cellular respiration is a process that all living things use to convert glucose into energy. Autotrophs (like plants)\u00a0produce glucose during photosynthesis. Heterotrophs (like humans) ingest other living things to obtain glucose. While the process can seem complex, this page takes you through the key elements of each part of cellular respiration.\r\n\r\nCellular respiration is a collection of three unique metabolic pathways: glycolysis, the citric acid cycle, and the electron transport chain.\u00a0Glycolysis is an anaerobic process, while the other two pathways are\u00a0aerobic. In order to move from glycolysis to the citric acid cycle, pyruvate molecules (the output of glycolysis) must be oxidized in a process called pyruvate oxidation.\r\n

Glycolysis<\/h2>\r\nGlycolysis is the first pathway in cellular respiration. This pathway is anaerobic and takes place in the cytoplasm of the cell.\u00a0This pathway\u00a0breaks down 1 glucose molecule and produces 2 pyruvate molecules.\u00a0There are two halves of glycolysis, with five steps in each half.\u00a0The first half is known as the \"energy requiring\" steps. This half\u00a0splits glucose, and uses up 2 ATP.\u00a0If the concentration of pyruvate kinase is high enough, the second half of glycolysis can proceed.\u00a0In the second half, the \"energy releasing: steps, 4 molecules of ATP and 2 NADH are released.\u00a0Glycolysis has a net gain\u00a0<\/strong>of\u00a0<\/strong>\u00a02 ATP molecules and 2 NADH.\r\n\r\nSome cells (e.g., mature mammalian red blood cells) cannot undergo aerobic respiration, so glycolysis is their only<\/strong> source of ATP. However, most cells undergo pyruvate oxidation and continue\u00a0to the other pathways of cellular respiration.\r\n

Pyruvate Oxidation<\/h2>\r\nIn eukaryotes, pyruvate oxidation\u00a0takes place in the mitochondria. Pyruvate oxidation can only happen if oxygen is available. In this process, the\u00a0pyruvate created by glycolysis is oxidized. In this oxidation process,\u00a0a carboxyl group is removed from pyruvate, creating\u00a0acetyl groups, which compound with coenzyme A (CoA) to form acetyl CoA.\u00a0This process also releases CO2<\/sub>.\r\n

Citric Acid Cycle<\/h2>\r\nThe citric acid cycle (also known as the Krebs cycle) is the second pathway in cellular respiration, and it also takes place in the mitochondria. The rate of the cycle is controlled by ATP concentration. When there is more ATP available, the rate slows down; when there is less ATP the rate increases.\u00a0This pathway is a closed loop: the final step produces the compound needed for the first step.\r\n\r\nThe citric acid cycle is considered an aerobic pathway because the\u00a0NADH and FADH2<\/sub> it produces act as temporary electron storage compounds, transferring their electrons to the next pathway (electron transport chain), which uses atmospheric oxygen.\u00a0Each turn of the citric acid cycle provides a net gain <\/strong>of\u00a0CO2<\/sub>, 1 GTP or ATP, and\u00a03 NADH and 1\u00a0FADH2<\/sub>.\r\n

Electron Transport Chain<\/h2>\r\nMost ATP from\u00a0glucose is generated in the electron transport chain. It\u00a0is the only part of cellular respiration that directly consumes oxygen; however, in some\u00a0prokaryotes, this is an anaerobic pathway.\u00a0In eukaryotes, this pathway takes place in the inner mitochondrial membrane. In\u00a0prokaryotes\u00a0it occurs in the plasma membrane.\r\n\r\nThe electron transport chain is made up of 4 proteins along the membrane and a proton pump. A\u00a0cofactor shuttles electrons between proteins I\u2013III. If NAD is depleted, skip I: FADH2<\/sub> starts on II.\u00a0In chemiosmosis, a proton pump takes hydrogens from inside mitochondria to the outside; this spins the \u201cmotor\u201d and the phosphate groups attach to that.\u00a0The movement changes from ADP to ATP, creating 90% of ATP obtained from aerobic glucose catabolism.\r\n

Let's Practice<\/h2>\r\nNow that you've reviewed cellular respiration,\u00a0this practice activity will help you see how well you know\u00a0cellular respiration:\r\n\r\n