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Lecture 19 - LECTURE 19 05 October 2011(P J Hollenbeck...

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LECTURE 19 05 October 2011 (P. J. Hollenbeck) BIOL231 Mitochondria: TCA cycle, electron transport, and ATP synthesis Read: pp. 436-446; 453-476 + DVD 13.2, 14.1 - 14.4 Problems: 7.1 - 7.3; Exam II‘09, #10; Exam II‘10, #1 and #6 I. Structure and function of the mitochondrion ( DVD 14.1 ) (A) Compartmental organization Matrix and IMS. The two membranes of the mitochondrion create two compartments, a space contained by the inner membrane, called the matrix, and a space between the inner and outer membrane, called the intermembrane space, or IMS (see figs 14-4,-7 ). Although the mitochondria are not part of the endomembrane system of the cell, we still need to establish a convention for describing the topology of these spaces. Remember that when the Ä G for ion flow across a membrane is negative, it means that it is energetically favorable for it to flow into the cytoplasm. What about ion movement across the inner mitochondrial membrane? (B) Membranes (1) The outer membrane is in contact with the cytoplasm and has a composition generally similar to that of other membranes in the cell. It is very permeable (“leaky”) to most solutes with molecular weights below 5 kD. This permeability is largely due to the presence of integral membrane proteins called porins that form channels (made of parallel â -sheets) through the membrane ( fig. 11-25 ). Thus, if you are a small molecule (say, ATP or ADP) you can move freely between the cytoplasm and the IMS, so the IMS has a similar composition to the cytoplasm. (2) The inner mitochondrial membrane is very different: it has a very high protein content , 75% protein and, like bacterial membranes, has no cholesterol. The integral membrane proteins include a variety of transporters, the proteins of the electron transport chain, and ATP synthase. The inner membrane is also very impermeable to solutes but has numerous transporters to manage the exchange of specific molecules between the MATRIX and the IMS. The inner membrane is also deeply and variably infolded, giving it a large surface area relative to the size of the mitochondrion.
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<Which stages of the total oxidation of glucose occur in mitochondria, and how are they organized?> II. The TCA Cycle (everything here occurs in the mitochondrial matrix; see DVD 13-2 !) <here, the cell will harvest energy from coupled reactions at 6 steps out of 9 total (compare this to glycolysis)> (A) Harvesting high energy electrons (:H ions) : move once through the cycle [ Fig. 13-11 ] (1) Recall that pyruvate (3C) is the product of glycolysis. It enters the TCA cycle in an indirect way: it combines with coenzyme A (“CoA”) to produce acetyl-coA (2C) and 1 2 CO . In this reaction, a pair of electrons (hydride ion) is transferred to NAD to + produce 1 NADH .
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