Which molecule is 6C

am Puls Biologie 5, textbook

57 Cell metabolism Glucose is broken down in glycolysis Let us now follow the path of the breakdown processes in cell respiration step by step. Glucose first has to be channeled into the cell before it can be broken down in the cytoplasm. In glycolysis, glucose, a molecule made up of 6 carbon atoms, is then converted into two lower-energy C3 molecules. Pyruvate is formed in several steps. First of all, energy in the form of ATP has to be invested in glycolysis in order to activate the glucose molecule. In the next steps of glycolysis, however, energy and electrons are released, which are stored in the form of ATP and NADH. Glycolysis is divided into an energy investment phase and an energy generation phase. Glycolysis produces two ATP and two NADH molecules per glucose molecule. Glucose is broken down into 2 molecules of pyruvate in the cytoplasm during glycolysis. Pyruvate is broken down in the citric acid cycle. The next step in cell respiration occurs in the cell's power stations, the mitochondria (k Fig. 19). You already know that mitochondria are elongated cell organelles that are enclosed by a double membrane. The pyruvate formed in glycolysis is transported by the cytoplasm to the mitochondria for further breakdown. First of all, acetic acid (acetyl-CoA, a molecule with two carbon atoms) is produced from pyruvate. The third carbon atom of the pyruvate is already separated off as CO 2 in this reaction. In addition, NADH + H + is formed through the transfer of electrons. The activated acetic acid binds to oxaloacetate, a molecule with four carbon atoms, and thus forms a C6 molecule called citrate (citric acid). The entire reaction cycle is named after this molecule: the citric acid cycle. Through a cyclical sequence of reactions, citrate is now broken down into CO 2 and oxaloacetate, which in turn is required in the first step of the citric acid cycle. The yield of the citric acid cycle in one circulation is one ATP, three NADH and one FADH 2. Two pyravate molecules (C3) were formed per glucose molecule, so the citric acid cycle must be run through twice to break down a glucose molecule. The total yield for one molecule of glucose is two ATPs. That is still very little, since glucose is a very high-energy molecule. The release of energy is far from complete. The electrons that were released were initially only temporarily stored in NADH and FADH 2. The final electron acceptor, oxygen, does not wait until the end of the respiratory chain. This is where most of the energy is released in cell respiration. In the mitochondria, pyruvate is broken down into CO 2 in the citric acid cycle. Tasks S1 Glycolysis and the citric acid cycle take place in different parts of the cell. Explain the possible advantages and disadvantages of such a separation. S 2 When your body cells breathe, CO 2 and H 2 O are the end products. Think about which of the two compounds contains the inhaled oxygen and give reasons for your conclusion. Basic concept of structure and function: The double membrane that encloses the mitochondria is essential for a proton gradient to be built up. The respiratory chain takes place in the mitochondria. The release of energy in the respiratory chain occurs on the inner mitochondrial membrane and in the intermembrane space (k Fig. 19). The inner mitochondrial membrane contains four large protein complexes (I – IV), which are collectively referred to as the respiratory chain (k Fig. 20). These four complexes can transfer electrons along an electron transport chain because they have different redox potentials (see p. 51). The electron flow occurs from the intermembrane space through the inner mitochondrial membrane into the mitochondrial matrix, the electrons are energetically passed “downhill”. You already got to know a similar electron transport during photosynthesis. The electrons obtained are transferred to the oxygen in the respiratory chain. Fig.19: Mitochondrion. Mitochondria are the power plants of the cell. The respiratory chain runs on the inner mitochondrial membrane and in the space between the two membranes. inner mitochondrial membrane intermembrane space For testing purposes only - property of the publisher öbv

Made with FlippingBook

RkJQdWJsaXNoZXIy ODE3MDE =