etc solutions – Flashcards

The long isoprenoid side chain makes ubiquinone very soluble in lipids and allows it to diffuse in the semifluid membrane. This is important because ubiquinone transfers electrons from Complexes I and II to Complex III, all of which are embedded in the inner mitochondrial membrane.

(a) Cyanide inhibits cytochrome oxidase (a a3); all carriers become reduced. (b) In the absence of O2, no terminal electron acceptor is present; all carriers become reduced. (c) In the absence of NADH, no carrier can be reduced; all carriers become oxidized. (d) These are the usual conditions for an aerobic, actively metabolizing cell; the early carriers (e.g., Q) are somewhat reduced, while the late ones (e.g., cytochrome c) are oxidized.

(a) The inhibition of NADH dehydrogenase by rotenone decreases the rate of electron flow through the respiratory chain, which in turn decreases the rate of ATP production. If this reduced rate is unable to meet its ATP requirements, the organism dies. (b) Antimycin A strongly inhibits the oxidation of reduced Q in the respiratory chain, severely limiting the rate of electron transfer and ATP production. (c) Electrons flow into the system at Complex I from the NAD-linked reactions and at Complex II from succinate and fatty acyl-CoA through FAD (see Figs. 19-8 and 19-16). Antimycin A inhibits electron flow (through Q) from all these sources, whereas rotenone inhibits flow only through Complex I. Thus, antimycin A is a more potent poison.

2.5

At relatively low levels of an uncoupling agent, P/O ratios drop somewhat, but the cell can compensate for this by increasing the rate of electron flow; ATP levels can be kept relatively normal. At high levels of uncoupler, P/O ratios approach zero and the cell cannot maintain ATP levels.

The observed effects are consistent with the action of an uncoupler—that is, an agent that causes the free energy released in electron transfer to appear as heat rather than in ATP. In respiring mitochondria, H ions are translocated out of the matrix during electron transfer, creating a proton gradient and an electrical potential across the membrane. A significant portion of the free energy used to synthesize ATP originates from this electric potential. Valinomycin combines with K ions to form a complex that passes through the inner mitochondrial membrane. So, as a proton is translocated out by electron transfer, a K ion moves in, and the potential across the membrane is lost. This reduces the yield of ATP per mole of protons flowing through ATP synthase (FoF1). In other words, electron transfer and phosphorylation become uncoupled. In response to the decreased efficiency of ATP synthesis, the rate of electron transfer increases markedly. This results in an increase in the H gradient, in oxygen consumption, and in the amount of heat released.

DCCD (like oligomycin) inhibits ATP synthesis. In tightly coupled mitochondria, this inhibition leads to inhibition of electron transfer also

A decrease in electron transfer causes a decrease in O2 consumption. 2,4-Dinitrophenol uncouples electron transfer from ATP synthesis, allowing respiration to increase. No ATP is synthesized and the P/O ratio decreases.

Malate dehydrogenase catalyzes the conversion of malate to oxaloacetate in the citric acid cycle, which takes place in the mitochondrion, and also plays a key role in the transport of reducing equivalents across the inner mitochondrial membrane via the malate-aspartateshuttle

(a) If n-butylmalonate, an inhibitor of the malate-a-ketoglutarate transporter, is added to cells, NADH accumulates in the cytosol. This forces glycolysis to operate anaerobically, with reoxidation of NADH in the lactate dehydrogenase reaction. (b) Because reducing equivalents from the oxidation reactions of glycolysis do not enter the mitochondrion, oxygen consumption slows and eventually ceases. (c) The end product of anaerobic glycolysis, lactate, accumulates. (d) ATP is not formed aerobically because the cells have converted to anaerobic glycolysis. Overall, ATP synthesis decreases drastically, to 2 ATP per glucose molecule.

(a) Oxygen allows the tissue to convert from lactic acid fermentation to respiratory electron transfer and oxidative phosphorylation as the mechanism for NADH oxidation. (b) Cells produce much more ATP per glucose molecule oxidized aerobically, so less glucose is needed. (c) As [ATP] rises, phosphofructokinase-1 is inhibited, thus slowing the rate of glucose entry into the glycolytic pathway.

The absence of cytochrome oxidase prevents these mutants from oxidizing the products of fermentation (ethanol, acetate, lactate, or glycerol) via the normal respiratory route. These mutants do not have a working citric acid cycle because they cannot reoxidize NADH through the O2-dependent electron-transfer chain. Thus, catabolism of glucose stops at the ethanol stage, even in the presence of oxygen. The ability to carry out these fermentations in the presence of oxygen is a major practical advantage because completely anaerobic conditions are difficult to maintain. The Pasteur effect—the decrease in glucose consumption that occurs when oxygen is introduced—is not observed in the absence of an active citric acid cycle and electron-transfer chain.

What term describes the presence of both normal and mutated mitochondrial DNA (mtDNA), resulting in variable expression in mitochondrial inherited diseases?

Pyruvate dehydrogenase is located in the mitochondrion, and glyceraldehyde 3-phosphate dehydrogenase in the cytosol. Because the mitochondrial and cytosolic pools of NAD are separated by the inner mitochondrial membrane, the enzymes do not compete for the same NAD pool. However, reducing equivalents are transferred from one nicotinamide coenzyme pool to the other via shuttle mechanism

The malate-aspartate shuttle transfers electrons and protons from the cytoplasm into the mitochondrion. Neither NAD nor NADH passes through the inner membrane, thus the labeled NAD moiety of [7-14C]NADH remains in the cytosol. The 3 H on [4-3 H]NADH enters the mitochondrion via the malate-aspartate shuttle (see Fig. 19-29). In the cytosol, [4-3 H]NADH transfers its 3 H to oxaloacetate to form [3 H]malate, which enters the mitochondrion via the malate- -ketoglutarate transporter, then donates the 3 H to NAD to form [4-3 H]NADH in the matrix.

(1) electron donor and reducing agent

(1) electron acceptor and oxidizing agent

(2) electron donor and reducing agent

(2) electron acceptor and oxidizing agent

(3) electron donor and reducing agent

(3) electron acceptor and oxidizing agent

The effect of replacing ATP4- with ADP3- in the matrix is the net efflux of one negative charge, which is favored by the charge difference across the inner membrane (outside positive) an antiporter that brings ATP out of the matrix into the ims and ADP into the matrix from the ims

-is a symporter that allows a H+ to flow down its concentration gradient and simultaneously brings a phosphate group along into the matrix; is specific for H2PO4-. There is no net flow of charge during symport of H2PO4- and H+, but the relatively low proton concentration in the matrix favors the inward movement of H+. Thus the proton-motive force is responsible both for providing the energy for ATP synthesis and for transporting substrates (ADP and Pi) into and product (ATP) out of the mitochondrial matrix.

This alternative means of moving reducing equivalents from the cytosol to the mitochondrial matrix operates in skeletal muscle and the brain. In the cytosol, dihydroxyacetone phosphate accepts two reducing equivalents from NADH in a reaction catalyzed by cytosolic glycerol 3-phosphate dehydrogenase. An isozyme of glycerol 3-phosphate dehydrogenase bound to the outer face of the inner membrane then transfers two reducing equivalents from glycerol 3-phosphate in the intermembrane space to ubiquinone. Note that this shuttle does not involve membrane transport systems.

protein complex in the mitochondrial inner membrane and the bacterial plasma membrane that consists of the F1 complex bound to the Fo complex; the flow of protons through the Fo component leads to the synthesis of ATP by the F1 component.

produces low rates of glycolysis, pyruvate oxidation, acetate oxidation via the citric acid cycle, and oxidative phosphorylation. All four pathways are accelerated when the use of ATP and the formation of ADP, AMP, and Pi increase.

inhibits glycolysis, supplements the action of the adenine nucleotide system

also inhibit the oxidation of pyruvate to acetyl-CoA

inhibits the dehydrogenase reactions of TCA

As amounts of an uncoupler increase, the P/O ratio decreases and the body struggles to make sufficient ATP by oxidizing more fuel. The heat produced by this increased rate of oxidation raises the body temperature

Increased activity of the respiratory chain in the presence of an uncoupler requires the degradation of additional energy stores (glycogen and fat). By oxidizing more fuel in an attempt to produce the same amount of ATP, the organism loses weight

Defects in Complex II result in increased production of ROS, damage to DNA, and mutations that lead to unregulated cell division (cancer) cancer cells are in an altered metabolic state; mutations in mitochondrial DNA encoded genes can contribute to the development of cancer. It is possible that such mutations provide metabolic adaptivity to the cancer cell