We also learned about the digestive system and its function from the mouth to the rectum and out the body. We did an activity where we got a bagel and put it through the digestive system. Each person in the class was an organ, enzyme or another important part of digesting food. We went step by step through every part of the digestive tract until we wee at the rectum to find that the bagel was mushed and digested into a wet mess (thank god it was in a zip lock bag). We learned about digestive enzymes such as salivary amylase which digests carbohydrates such as starch, pancreatic amylase, lipase and nucleases digesting food in the small intestine, and pepsin that digests protein.
We also learned about cell respiration. Cell Respiration is the process by which chemical energy of food molecules is released and partially captured in the form of ATP. Carbohydrates, fats, and proteins can be used as fuels for cell respiration. Glycolysis, and if oxygen is available, Krebs cycle and electron transport chain (oxidative phosphorolation). If oxygen is not available fermentation begins after glycolysis. Glycolysis occurs in the cytoplasm and does not need oxygen. The 6 carbon molecule glucose is broken down in the investment and pay off phase into two, three carbon molecules called pyruvate. Glycolysis uses 2 ATP's to produce 4ATP's. the net gain of ATP's is 2. An NADH + H is formed in glycolysis (substrate level phosphorolation). The intermediate step before reaching Krebs cycle occurs after glycolysis and oxidizes the pyruvate molecules. A carbon from each pyruvate releases a CO2 and forms 2, 2 carbon molecules called Acetyl CoA. An NAD+ is reduced to form NADH for each molecule. This occurs in the matrix of the mitochondria. The next step is the Krebs cycle which is substrate level phosphorolation and occurs in the matrix. Also known as the Citric Cycle, the cycle generates a pool of chemical energy from the oxidation of pyruvate. The 2 carbon molecule from the intermediate step joins a free floating 4 carbon molecule created through evolution and makes a 6 carbon molecule called citrate (enzyme catalyzed reaction). Citrate goes through the cycle and loses 2 carbons releasing as CO2 making a 4 carbon molecule. During this cycle, NAD+ reduces to NADH three times for each molecule. 1 ATP is made and 1 FADH2 is made for each molecule. A total of 6 NADH + 6H, 2 ATP and 2FADH2 is made in Krebs Cycle. From glycolysis, int. phase and krebs cycle, a total of 10 NADH, 2FADH2 and 4ATP are created. The next 34 ATP are produced in the ETC and Chemiosmosis. The cristae contain protein complexes where the electron carriers, NADH and FADH2 drop off and release a pair of electrons. Each electron pair in transferred from a high level of energy to a low energy level. In this process, energy is released during the redox reactions to make ATP. Electrons provide the energy to pump protons across the membrane into the inter membrane space creating a H+ gradient. The matrix becomes more basic while the inter-membrane space becomes more acidic. The protons want to diffuse back into the matrix going from a high concentration to a low concentration. Chemiosmosis occurs as the hydrogens act as a generator and move through the enzyme ATP synthase into the matrix. ATP synthase has a rector that spins and creates electrical movement joining ADP and Phosphate substrates to make an end product of ATP. For each NADH, 3ATPS's are made. For each FADH2, 2 ATP's are made. This makes an average of 34 ATP's made in chemiosmosis. A total amount of ATP's made from all steps average to 38 ATP's. Electrons join with oxygen in ETC and attract protons to form H2O or water. As shown, oxygen drives this process.
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