Cellular Respiration

Jerry J. Zimmerman , ... Jerry McLaughlin , in Pediatric Critical Care (Fourth Edition), 2011

Respiration, Metabolic Pathways

Glycolysis

As previously indicated, cellular respiration allows controlled release of free free energy from carbohydrate, fat, and protein free energy substrate. Cellular respiration consists of three related series of biochemical reactions:

one.

Degradative reactions resulting in the germination of acetyl coenzyme A and reducing equivalents

two.

Metabolism of acetate to carbon dioxide in the Krebs bicycle with generation of additional reducing equivalents

three.

Shuttling of electrons generated from reducing equivalents forth the mitochondrial electron transport chain

Acetate coupled to coenzyme A (AcCoA) is derived from carbohydrates, lipids, and proteins. Glucose is transported into cells via glucose transporter (Overabundance) receptors and osmotic gradients (see Chapter 77). Ten enzymatic reactions inside the prison cell cytoplasm define the metabolic pathway, termed glycolysis. These initial serial of reactions ultimately generate two net molecules of ATP, two molecules of NADH, and two molecules of pyruvate.

The fates of pyruvate is multiple. Under anaerobic conditions, pyruvate may be reduced by NADH to lactate to regenerate NAD+. Alternatively, pyruvate is shuttled to the mitochondria, where it is further metabolized to carbon dioxide (CO2) and AcCoA. Pyruvate transamination yields alanine, whereas pyruvate carboxylase generates oxylacetate (Figure 74-6).

Catabolism of fatty acids by β-oxidation generates one molecule of AcCoA and i molecule each of FADH2 and NADH for each two-carbon fatty acid fragment cycle. These reactions occur in the mitochondria afterward fatty acid transport past a carnitine transport system. It should exist appreciated that generation of AcCoA past fatty acid β-oxidation occurs contained of pyruvate dehydrogenase that can exist rate limiting for complete glucose metabolism. Especially as an attribute of the metabolic stress response mediated by cortisol, catecholamines, and interleukins 6 and 2, protein degradation can occur with release of amino acids. All amino acids may be catabolized to either AcCoA or some Krebs cycle intermediate. Accordingly, amino acids tin can be mobilized for energy production as well every bit de novo poly peptide synthesis. Alternatively, amino acids can undergo gluconeogenesis, a costly procedure that basically requires four ATP molecules plus ii GTP molecules and 2 NADH molecules to regenerate one molecule of glucose from two molecules of pyruvate (run into Chapter 77). ATP and GTP for these series of reactions are provided by β-oxidation of fatty acids.

Pyruvate is metabolized in the mitochondria to AcCoA and CO2 via pyruvate dehydrogenase, a large polyhedral protein complex with molecular weight of 10 × ten6 Da. Thiamin, lipoic acid, magnesium, and coenzyme A serve as cofactors for this reaction, which represents the starting time irreversible stride in terms of mitochondrial oxidation of pyruvate. This key reaction is regulated past a family of pyruvate dehydrogenase kinases. As noted above, AcCoA is too generated inside the mitochondria past β-oxidation of fatty acids. Two molecules of AcCoA may condense to grade acetyl acetate, which can after be metabolized to β-hydroxy butyrate and acetone, all of which may be used as energy substrate past the middle, brain, and skeletal muscle during fasting after a depletion of glycogen stores.

Krebs Cycle

The Krebs bike summarizes a round series of reactions in the mitochondria to metabolize AcCoA to two molecules of COtwo with resultant generation of one molecule of GTP, iii molecules of NADH, and ane molecule of FADH2. GTP is equivalent to ATP in terms of free energy charge. Although oxygen itself is not part of the Krebs cycle, its presence at the end of the mitochondrial electron transport chains ensures recycling of NAD+ and FAD required in the Krebs cycle (Figure 74-vii).

AcCoA, derived from glucose, fatty acids, or poly peptide catabolism, condenses with oxaloacetate in step 1. One rotation of reactions in the mitochondria metabolizes the AcCoA to two molecules of CO2, generates 1 ATP equivalent in the form of GTP, and generates reducing equivalents in the class of NADH and FADH2.

Electron Ship Chain

Electrons derived from reducing equivalents NADH and FADH2 are shuttled along the mitochondrial electron send chain, ultimately reducing molecular oxygen to h2o. Basically, for each pair of electrons involved in one hydride equivalent, 3 molecules of ATP are produced. Five complexes of proteins and cytochromes comprise the mitochondrial electron ship chain and facilitate a stride-down period of FADH2 and NADH reduction potential along the inner membrane of the mitochondria. These redox reaction complexes include NADH dehydrogenase–ubiquinone oxidoreductase (complex 1), succinate dehydrogenase–ubiquinone oxidoreductase (complex 2), ubiquinone–cytochrome C oxidoreductase (circuitous three), cytochrome c oxidase (complex 4), and ATP synthase (circuitous 5). Electrons in the form of hydride ions from NADH and FADH2 pour along these protein/cytochrome complexes toward molecular oxygen. Protons generated during these reactions are pumped across the inner mitochondrial membrane matrix into the intermembrane infinite, generating a proton motive force. The proton electrochemical slope across the inner mitochondrial membrane drives ATP synthesis past a reaction that has been termed chemiosmosis. 41 Energy for ATP synthesis arises from an influx of these protons dorsum into the matrix, literally through the rotary motor of ATP synthase. 42

The proton pore involves the c-ring and the a-protein. The rotary component is the coiled-gyre γ-subunit, which is jump to the ε-subunit and to the c-ring. The stationary component is the hexameric α3β3 unit of measurement and is fixed by the δ, b, and a proteins (Effigy 74-8).

Although multiple regulatory steps exist along the respiration metabolic pathways, the following 3 are prominent:

ane.

Oxygen availability to serve as the ultimate electron acceptor. This will depend on oxygen delivery to the tissue equally well every bit regulation of oxygen bounden to the heme moiety of cytochrome oxidase by NO, as previously discussed.

2.

Availability of nutrient metabolism to generate reducing equivalents in the grade of NADH

and FADH2, equally previously noted. Depletion of NADH can occur in instances of

astringent cellular stress after activation of the PARP.

three.

Overall cellular energy land defined past the ratio of ATP/ADP.

Specific adenine nucleotide translocase on the inner mitochondrial membrane as well as a voltage-dependent ion channel representing the virtually abundant poly peptide of the outer mitochondrial membrane facilitate ATP send out of the mitochondria for use as free energy currency for all cellular functions.

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TISSUE RESPIRATION | Cellular Respiration

1000.B. McClelland , in Encyclopedia of Fish Physiology, 2011

Abstract

Cellular respiration constitutes the primary oxygen-consuming and adenosine triphosphate (ATP)-producing processes. Whole-animal metabolic rate is the sum of respiration from all tissues combined. ATP production past oxidative phosphorylation (OXPHOS) requires adequate delivery of both oxygen and metabolic fuels to cells. While environmental levels of oxygen (east.thousand., atmospheric or dissolved oxygen) and the pathway from gas-transfer organs to tissues decide oxygen delivery, fuels tin be fatigued from stores inside the trunk. The pathway for oxygen from the environs to mitochondria involves the processes of diffusion and convective transport. The delivery of nonesterified fatty acids (NEFAs), glucose, and amino acids additionally relies on protein must also rely on poly peptide transporters to cross membranes. While most, just not all, of the aspects of cellular respiration are shared across taxa, fish testify some unique characteristics. Probably the biggest difference betwixt mammals and fish are the fuels used to power musculus during exercise, and their plasticity in response to environmental and energetic stress. In addition, dissimilar fish groups tin can be thought of equally natural knockout models for sure aspects of the fuel and oxygen commitment systems. The elasmobranchs lack NEFA plasma transport proteins and a key fatty oxidation enzyme. Several species of Antarctic icefish lack the oxygen-transport proteins hemoglobin and myoglobin. Understanding how these species deal with the absence of these proteins provides windows into the regulation of fuel and oxygen-commitment pathways.

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Peroxidase Biochemistry and Redox Signaling

A. Bindoli , K.P. Rigobello , in Encyclopedia of Biological Chemistry (Second Edition), 2013

Cellular Respiration and Product of Reactive Oxygen Species

Cellular respiration sustains aerobic life and involves the oxidation of nutrients, with the last production of carbon dioxide and water. During this process, oxidation energy is captured in the grade of adenosine triphosphate (ATP) molecules. Nigh of the oxygen is reduced to water by cytochrome c oxidase in a 4-electron process. However, a minor percentage of oxygen (1–3%) can be converted to the superoxide anion ( O 2 • − ) in a mono-electronic procedure ( Figure one ), depending on the leak of single electrons, mostly released by the mitochondrial and microsomal electron transport chains. However, several other sources of superoxide anion are besides active in the cell. Superoxide undergoes dismutation to hydrogen peroxide (HiiOtwo), either spontaneously or in a superoxide dismutase-catalyzed reaction. In the presence of transition metals such as atomic number 26 or copper, the formation of the stiff oxidizing hydroxyl radical (•OH) is favored ( Figure 1 ). Superoxide anion, hydrogen peroxide, and hydroxyl radical are collectively called reactive oxygen species (ROS) and considered the master agents responsible for oxidative stress. Hydrogen peroxide is a relatively stable oxidant and, when its concentration in cells increases, it must be controlled by several enzymes, in detail, catalase and the peroxidases dependent on glutathione or thioredoxin (Trx). All the same, several peroxidases utilise H2O2 for defensive or biosynthetic purposes. Lastly, it is increasingly recognized that H2Otwo should be included among the cell-signaling molecules such as nitric oxide, calcium, and cyclic adenosine monophosphate (military camp). Hence, peroxidases, enzymes capable of breaking down H2O2 to HiiO, deed as modulators of the level of hydrogen peroxide, decision-making its office as a second messenger.

Figure one. Reduction of oxygen and formation of oxygen-complimentary radicals. Oxygen is largely reduced to water by the cytochrome oxidase complex, with the concomitant generation of energy in the form of ATP (left). However, a little oxygen tin can be reduced univalently, with the formation of reduced intermediates (right). The first reduction product is superoxide anion ( O ii • − ). Hydrogen peroxide is the ii-electron reduced course of oxygen. In the presence of reduced iron ions, hydrogen peroxide undergoes the Fenton reaction (H2Otwo  +   Fe(II)   →   Fe(Iii)   +   OH−  + •OH), leading to the formation of the highly oxidant hydroxyl radical (•OH). Lastly, hydroxyl radical can be reduced to water. Other metals, peculiarly copper, can catalyze the formation of •OH from H2O2.

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Energy Metabolism

Due south.Eastward. Cox , in Encyclopedia of Human Diet (Third Edition), 2013

Cellular Respiration and Adenosine Triphosphate (ATP)

Cellular respiration tin can be defined more often than not equally the procedure by which chemical energy is released during the oxidation of organic molecules. If it requires oxygen it is called aerobic respiration, whereas if it takes place in the absenteeism of oxygen it is anaerobic respiration.

Organic molecules, unremarkably carbohydrate or fat are broken down by a series of enzyme-catalyzed reactions. Many of these reactions release a small corporeality of energy that is channeled into molecules of a chemical nucleotide called adenosine triphosphate or ATP (Figure 1).

Figure ane. Structure of adenosine triphosphate (ATP).

ATP is the standard unit of measurement in which the energy released during respiration is stored. ATP is an instant source of energy within the cell. Information technology is mobile and transports energy to wherever energy-consuming processes are occurring within the prison cell. The energy is released by the dephosphorylation of ATP to adenosine diphosphate (ADP), which can and so be rephosphorylated to ATP thorough coupling to the processes of respiration. ATP is establish in all living cells and can exist thought of as a universal energy transducer.

The principle metabolic fuel is glucose and there are three stages in its oxidation to carbon dioxide, water, and energy; captured as ATP. This process tin be summarized very simply by the following equation:

C 6 H 12 O 6 + 6 O 2 → six CO 2 + six H 2 O + ENERGY ( ATP )

In the kickoff stages of glycolysis and the tricarboxylic acid bicycle, glucose, and other metabolic fuels are oxidized, linked to the chemical reduction of coenzymes (nicotinamide adenine dinucelotide (NAD+), flavin adenine dinucleotide (FAD), and flavin mononucleotide (FMN)). In the final stage, of oxidative phosphorylation via the hydrogen electron transfer chain, ATP is synthesized from ADP and phosphate using energy released from the oxidation and recycling of the reduced coenzymes (Table 1). Thus the oxidation of metabolic fuels is tightly coupled to energy consumption and the production of ADP from ATP in energy consuming processes (Figure 2).

Table one. The three principle stages in the product of ATP from 1 molecule of glucose

Metabolic pathway Where O2 required? Net ATP or reduced coenzymes/glucose Products
Glycolysis Cytoplasm Anaerobic Net gain Glucose→2 pyruvate
two ATP
2 NADH+H+
Pyruvate→acetyl-CoA Mitochondrial matrix Aerobic ii NADH+H+
TCA cycle Mitochondrial matrix Aerobic ii GTP→ii ATP 2 Pyruvate→6CO2
viii NADH+H+
2 FADHii
Electron transfer chain (oxidative phosphorylation) Mitochondrial crista and primary particles Aerobic 12 NAD++ii FAD→38 a ATP 12Htwo+6O2→6HiiO
a
The exact net gain in the number of ATP produced from the oxidation of the reduced coenzymes NAD+H and FADH can vary dependent on the machinery used to transport them across the crista membrane in the mitochondria, the site of oxidative phosphorylation.

Figure two. Linkage between ATP utilization in physical and chemical work and the oxidation of metabolic fuels.

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Conversion of α-Helical Proteins into an Culling β-Amyloid Fibril Conformation

Jason C. Collins , Lesley H. Greene , in Bio-nanoimaging, 2014

Prosthetic All α-Helical Proteins

Cellular respiration via the electron transport chain is present in eukaryotic and prokaryotic organisms. Two small all α-helical c-type cytochrome proteins, both functioning every bit electron-transport molecules, accept been shown to form amyloid fibrils under unique methodologies. Both cytochrome c 552 from Hydrogenobacter thermophilus (Fig. 43.5C) and bovine middle cytochrome c (Fig. 43.5D) covalently demark a haem group in their native structure and comprise 80 amino acids and 104 amino acids, respectively. In the instance of cytochrome c 552 Cys11Ala/Cys14Ala variant, there is a clear structural destabilization of the native construction upon loss of the haem grouping [59]. This destabilization allows this small all α-helical protein to form into amyloid-like fibrils nether physiologic weather (Table 43.1) [59]. The presence of thioether linkages to haem may indicate why cytochrome c 552 does non form amyloid fibrils in vivo, and may point an evolutionary step in avoiding amyloid fibrillation. Withal, another approach, using bovine cytochrome c, indicates that damage, but not removal, of the haem group also results in the formation of amyloid aggregates as the protein adopts a predominant random roll to let for conformational rearrangement [60].

Another prosthetic protein, not related to a illness, that has been shown to form amyloid fibrils in vitro is myoglobin (Fig. 43.5E). The nigh usually described function of myoglobin is the storage of dioxygen in muscles; however, it has also been described in nitric oxide scavenging and as a hypoxic nitrite reductase [61–63]. Later removal of its haem group, apomyoglobin was induced to form amyloid fibrils nether the basic weather shown in Table 43.1 [64]. Interestingly, apomyoglobin maintains its helical content later on removal of the haem group under mild conditions (22°C), whereas at 65°C apomyoglobin is dramatically is destabilized, resulting in fibrillation [64]. However, investigation into this process revealed that, at a college temperature (i.e. 90°C), fibrillation is significantly disrupted, whereas at a lower temperature (i.e. fifty°C) protein folding appears to suppress the germination of amyloid fibril structures [6]. Mutations of wild-type myoglobin, such as Trp7Phe/Trp14Phe, destroy the ability of myoglobin to bind its haem group, and Val10 significantly reduces its stability, assuasive this α-helical poly peptide to form amyloid fibrils at physiological pH [65–67]. It appears that the evolution of protein role with prosthetic groups, such as haem, seems to also function as a stabilizing cistron that prevents these types of proteins from forming amyloid fibrils in vivo.

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Harmful and Protective Effects of Terpenoids from African Medicinal Plants

Armelle T. Mbaveng , ... Victor Kuete , in Toxicological Survey of African Medicinal Plants, 2014

19.3.2 Inhibition of Cellular Respiration

In cellular respiration, taking place in mitochondria, ATP is generated. This energy is essential for all cellular and organic functions making respiration a vulnerable target in animals. Institute metabolites can set on this target with HCN, which binds to fe ions of the concluding cytochrome oxidase in the mitochondrial respiratory chain [13]. HCN does not occur in a gratis grade, but is stored as cyanogenic glycosides in institute vacuoles [thirteen]. A establish's cytosolic enzymes, such as β-glucosidase and nitrilase, hydrolyze the cyanogenic glycosides and the extremely toxic HCN is released [thirteen]. The diterpene atractyloside (5) (Figure 19.1) is a potent inhibitor of the mitochondrial ADP/ATP transporter and thus inhibits the ATP supply of a cell [13]. Atractyloside is an inhibitor of the adenine nucleotide translocator that inhibits oxidative phosphorylation by blocking the transfer of adenosine nucleotides through the mitochondrial membrane [16].

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Arsenic and Cancer

Paul B. Tchounwou , ... Sanjay Kumar , in Handbook of Arsenic Toxicology, 2015

23.iii.v Arsenic Distortion of Protein Structure

Arsenic impairs cellular respiration past inhibiting various mitochondrial enzymes, and the uncoupling of oxidative phosphorylation. Toxic by-products are released when arsenic interacts with sulfhydryl groups of proteins and enzymes, and substitutes phosphorus in a diversity of biochemical reactions [72]. For example, dihydrolipoyl dehydrogenase and thiolase enzymes are inactivated when arsenic reacts with their sulfhydryl groups causing inhibited oxidation of pyruvate and beta-oxidation of fatty acids. Arsenic likewise distorts the conformation of protein structure past attacking the disulfide bonds and thiol groups and binding to vicinal cysteines [73]. Arsenites interfere with sulfhydryl group of amino acids and disturb protein structure, while arsenates substitute for phosphate, affecting cellular processes such as ATP and DNA synthesis [74].

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An Overview of the Anatomy and Physiology of the Lung

H.H. Aung , ... Shadab Doctor , in Nanotechnology-Based Targeted Drug Delivery Systems for Lung Cancer, 2019

Abstract

Byproducts of cellular respiration, including carbon dioxide, must be removed from cells immediately, through the circulation and finally to the exterior of the body via the respiratory system to enable continuation of life and bodily functions. Understanding of the mutagenic development of cancers has led toward the development of novel treatment approaches, however an agreement of the basic architecture of the organ and its development helps. Therefore, in this chapter, the anatomy and physiology of the respiratory system are reviewed, including the embryonic development of the respiratory organisation followed by gross beefcake, innervation, blood circulation, and the microscopic structure of the lung and thoracic cavity. Then, the mechanism of breathing, pulmonary ventilation, and regulation of breathing are reviewed.

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Early Adventures in Biochemistry

In Foundations of Mod Biochemistry, 1995

Measurement of Oxygen Uptake

Studies on cellular respiration were technically more than hard than those on glycolysis because many of the enzymes are mitochondrial and so could non easily be solubilized. The earliest, semi-quantitative procedure for the micro-conclusion of oxygen utilization was that introduced past Thunberg ca. 1910 known as the Thunberg tube. The tissues which could be used were limited to those soft plenty to be chopped or put through a Latapie mincer (Szent-Gyorgi) which gave particles big enough to allow many of the cells to remain intact. After dispersal in a buffer the preparation could be pipetted. Oxidation was followed using nontoxic redox dyes such as methylene bluish whose color changed on oxidation or reduction. Many oxidizing systems were able to transfer electrons from substrates such as succinate to redox acceptors.

By the late 1920s quantitative micro-determination of oxygen uptake had been developed in Warburg's laboratory in Berlin based on a manometric technique introduced by Barcroft and Haldane (1902). With this equipment evolution of carbon dioxide or uptake of oxygen could exist monitored; Carbon dioxide produced in respiration was absorbed by potassium hydroxide. If bicarbonate buffer was used, acrid production caused carbon dioxide to be released. Krebs and others from Warburg'due south laboratory were skilled in designing assays which could exist adapted to manometric procedures (encounter Chapter vi). The ease with which measurements could be made by an experienced worker enabled kinetic analyses to exist performed speedily nether a diverseness of weather condition. Different ways of preparing tissues were also explored. Fred Waring, an American bandleader, marketed kitchen blenders (Waring blenders) which gave easily handleable suspensions, only intracellular organelles were often extensively damaged so that enzymes were rapidly inactivated. Alternatively the tissues were dispersed using a ability-driven, close-fitting pestle, originally fabricated of glass or stainless steel, but now usually of teflon (Potter-Elvejhem homogenizers). Cells were disrupted by the shearing force set upwards between the rotating pestle and the surrounding walls of the tube. The clearance of the pestle could exist selected so that nuclei and mitochondria were relatively undamaged.

Many of the early workers preferred to retain cell organization and diminish organelle damage by using tissue slices (Warburg, 1923). With a soft tissue like liver or kidney, these were cut by hand with a "cutthroat" razor or afterward, chopped mechanically. Rates of oxygen diffusion into the slices necessarily express their thickness. With a metabolically active tissue similar liver very sparse slices were desirable, which were patently fragile. There were also complications because the outer layer of cells was inevitably damaged.

A very different approach for measuring oxygen uptake now is to use an oxygen electrode with automatic recording. Dissolved oxygen tin be reduced electrolytically and this followed continuously by the change in potential. Originally a dropping mercury electrode was used (Vitek, 1933). By 1953 Clark had adult a system for small amounts of material where the electrode compartment was separated from the tissue past a cellophane membrane (at present "cling-film" or teflon) beyond which oxygen diffused rapidly. The method is fast and sensitive and since 1960 has become the method of selection for many respiratory studies.

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Specific Metals

Bruce A. Fowler , ... C.-J. Chen , in Handbook on the Toxicology of Metals (Fourth Edition), 2015

5.6.1 Mechanisms of Arsenical Metabolism and Toxicity

Arsenical inhibition of cellular respiration every bit a principal crusade of prison cell expiry has been appreciated for a number of decades ( ATSDR, 2007; NRC, 1999, 2001), and the methylation of inorganic arsenic to course methylated species such equally MMA and DMA has as well been studied for a number of decades (Braman and Foreback, 1973; Challenger, 1945, 1951). In contempo years, scientific attention has focused on trying to understand the relationships that must be between the in vivo methylation of inorganic arsenic and mechanisms of arsenical toxicity. This issue is of not bad practical importance because the methylation of inorganic arsenic was originally thought to be a detoxification pathway; withal, more recent studies (NRC, 1999) have suggested that highly toxic reactive oxygen species (ROS) generated by MMA(III) and DMA(3) mitochondrial toxicity may also play an important role in both the cellular toxicity and carcinogenicity of this element. The increased presence of MMA(Three) in the urine of a Mexican population exposed to inorganic arsenic in drinking water on a chronic ground was plant to course the ground for identifying subpopulations at a greater risk of arsenic-induced toxicity and cancer (Steinmaus et al., 2005a,b; Valenzuela et al., 2005). These studies also reported a strong link between dietary intakes of protein and other nutrients and the power to methylate arsenicals such that persons with low dietary intakes of these nutrients would be more susceptible than others to arsenic-induced cancers. The fundamental function of oxidative stress induced by arsenic in cell expiry via apoptosis or necrosis and carcinogenicity via oxidative impairment to cellular DNA cannot exist underestimated because it may permit attenuation of these deleterious cellular furnishings through nutritional interventions and stimulation of the cellular antioxidant systems.

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