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Does phosphorylation occur in photosynthesis
The catabolic pathways of glycolysis and respiration capture the chemical energy in glucose and other fuels and store it in ATP. Glycolysis, occurring in the cytosol, produces ATP, pyruvate, and NADH; the later two, may then enter the mitochondria for respiration. A mitochondrion consists of a matrix in which the enzymes of the krebs cycle are localized, a highly folded inner membrane (cristae) in which enzymes and the molecules of the electron transport chain (ETC) are embedded, and an intermembrane space between the two membranes, to temporarily house H+ that has been pumped across the inner membrane during the redox reactions of the ETC (a proton motive force (the definition is given below in the text) drives oxidative phosphorylation as protons move back through ATP synthases located in the membrane).
The coupling in oxidative phosphorylation uses a more complicated (and amazing!) mechanism, but the end result is the same: the reactions are linked together, the net free energy for the linked reactions is negative, and, therefore, the linked reactions are spontaneous.
Photophosphorylation occurs during photosynthesis
Phosphorylation of ADP (Equation 8) is coupled to the oxidation-reduction reaction of NADH and O2 (Equations 9 and 10). Electrons are not transferred directly from NADH to O2; rather, electrons pass through a series of intermediate electron carriers in the inner membrane of the mitochondrion. Why? This allows something very important to occur: the pumping of protons across the inner membrane of the mitochondrion. As we shall see, this proton pumping that is ultimately responsible for coupling the oxidation-reduction reaction to ATP synthesis.
Glycolysis, occurring in the cytosol, breaks glucose into two molecules of pyruvate. So partially oxidizes glucose (C6) into two pyruvate (C3) molecules. The Krebs cycle, which is a catabolic pathway, located in the mitochondrial matrix, converts a derivative of pyruvate (acetyl CoA) into carbon dioxide. In some of the steps of glycolysis and the krebs cycle, dehydrogenase enzymes transfer electrons to NAD+. NADH passes electrons to the electrons transport chain. This chain accepts energized electrons from reduce coenzymes NADH and FADH2. Energized electrons are harvested during glycolysis and Krebs cycle. Those electrons will eventually combine with hydrogen ions and oxygen to form water. The energy released in each step of the chain is used to synthesize ATP by oxidative phophorylation. Oxidative phosphorylation accounts for almost 90% of the ATP generated by respiration. About 10% of the ATP generated for each molecule of glucose oxidized to carbon dioxide and water is produced by substrate-level phosphorylation, in which an enzyme transfers a phosphate group from a substrate to ADP.
Chemistry for Biologists: Respiration
In glycolysis, each six-carbon glucose molecule is converted into two molecules of pyruvate. The next two stages of cellular respiration require oxygen. The Krebs cycle releases carbon dioxide and generates high-energy molecules. Oxidative phosphorylation, the last stage in cellular respiration, produces more ATP than any other metabolic pathway.
Which of the three stages of cellular respiration—glycolysis, the Krebs cycle, or oxidative phosphorylation—could organisms have used four billion years ago, before photosynthesis by cyanobacteria released oxygen into the atmosphere?
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Respiration What is respiration
To generate ATP, cells use a proton-pumping system made up of proteins inside the mitochondria to generate ATP. Before we examine the details of ATP synthesis, we shall step back and look at the big picture by exploring the structure and function of the mitochondria, where oxidative phosphorylation occurs.
Pentose phosphate pathway - Wikipedia
Two major types of mitochondrial proteins (see Figure 9, below) are required for oxidative phosphorylation to occur. Both classes of proteins are located in the inner mitochondrial membrane.
Georgia Virtual Learning > Home
The three major steps in oxidative phosphorylation are (a) oxidation-reduction reactions involving electron transfers between specialized proteins embedded in the inner mitochondrial membrane; (b) the generation of a proton (H+) gradient across the inner mitochondrial membrane (which occurs simultaneously with step (a)); and (c) the synthesis of ATP using energy from the spontaneous diffusion of electrons down the proton gradient generated in step (b).
AP Biology Animations - Biology Junction
For each glucose molecule entering glycolysis: 1) A net gain of two ATPs is produced by substrate-level phosphorylation. 2) Two molecules of NAD+ are reduced to NADH. Energy conserved in the high-energy electrons of NADH can be used to make ATP by oxidative phosphorylation. Energy-Investment phase includes five steps that split glucose in two and consumes ATP. So I do not expect you to memorize the structures or steps of glycolysis, but you should understand the process, where it occurs and the major molecules required and produced. For the different steps, see the text book.
Cellular Respiration Animation - Sumanas, Inc.
In order to couple the redox and phosphorylation reactions needed for ATP synthesis in the body, there must be some mechanism linking the reactions together. In cells, this is accomplished through an elegant proton-pumping system that occurs inside special double-membrane-bound organelles (specialized cellular components) known as mitochondria. A number of proteins are required to maintain this proton-pumping system and catalyze the oxidative and phosphorylation reactions.
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