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Lecture 5: "Mitochondria"

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Western University
Biology 2601A/B
Brown Jason

Organismal Physiology Lecture No. 5: Mitochondria th Tuesday September 25 , 2012 Introduction: -Mitochondria are the “powerhouses” of the cell. Their main function is to provide the energy necessary for cellular functions. Mitochondrial Structure: -By examining an electron micrograph, the mitochondria possess a double-membrane. The inner membrane is quite creased and these folds, known as cristae, increase the surface area of the mitochondrial inner membrane. This double-membrane also divides the mitochondria into two different compartments, the mitochondrial matrix and the intermembrane space. Mitochondria are more accurately represented as long coil of organelles and not merely individual objects. Primary Role: -The primary role of mitochondria is to produce the energy molecule known as ATP. Glycolysis: -The first pathway of cellular respiration that converts 1 molecule of glucose into 2 pyruvate, is an ancient, yet wasteful process. Most cells carry about this process, however it generates little ATP and most of the energy is contained within the pyruvate and NADH molecules, which are not used in glycolysis. The Origin Of Mitochondria: -Ancestral prokaryotic cells, containing a plasma membrane and no nucleus, originally only produced energy through glycolysis. Then, through the engulfing of other cells, these prokaryotes greatly increased in size as their plasma membrane enfolded in on itself, forming the basis for the nuclear envelope and later, the endoplasmic reticulum. -At this time, the beginnings of the eukaryotic cell were already under way. Aerobic bacteria were the first prokaryotes of their kind to utilize 2 to extract more energy as ATP. It was through the engulfing of aerobic bacteria by a eukaryotic cell that endosymbiosis became a reality. As the engulfed aerobe did not get digested by immediately by the eukaryotic cell, it took the waste products of glycolysis and made ATP from that. The ancestral eukaryote was now able to engage in oxidative metabolism. The Fate Of Pyruvate: -Mitochondria take up pyruvate, where pyruvate dehydrogenase oxidizes it to form the product Acetyl Co-A. This product is then run through the Citric Acid (Kreb’s) Cycle, where some energy from the original pyruvate and NADH is produced in the form of ATP. The Electron Transport Chain: -The electron transport chain is part of the final process of oxidative metabolism and occurs embedded in the inner mitochondrial membrane (along the cristae). All of the structures involved in the transport of electrons (ubiquinone, Cytochrome C and other complexes) are linked together in function. This process takes NADH molecules and extracts energy from them ultimately in the form of ATP. -An NADH molecule is oxidized to NAD , whereby it donates its pair of electrons to complex I and onto the ubiquinone where it is shuttled to complex III. Here the pair of electron is shuttle by Cytochrome C to complex IV where it binds with O in2the process of reducing it to water. Redox Potential & The Transfer Of Energy: -The structures and molecules involved in the electron transport chain are arranged in order of increasing redox potential (measure of affinity of a molecule for electrons) with NADH having the lowest affinity and O2having the highest. Every time an electron moves to a higher affinity molecule some energy is released. The Electrochemical Gradient & The Proton Motive Force: -The energy release from electron transfer is conserved as an electrochemical proton gradient and ultimately used to make ATP. This happens when the released energy moves the H ions (protons) into the intermembrane space at complexes I, III and IV respectively. This causes a high concentration of protons in the intermembrane space relative to the mitochondrial matrix. This build-up of protons provides a major source of potential energy. -The protons finally cross the inner mitochondrial membrane by
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