Two mitochondria from mammalian lung tissue displaying their matrix and membranes as shown by electron microscopy
The redox reactions of nicotinamide adenine dinucleotide.
Simplified structure of a mitochondrion.
UV absorption spectra of NAD and NADH.
Cross-sectional image of cristae in a rat liver mitochondrion to demonstrate the likely 3D structure and relationship to the inner membrane
Some metabolic pathways that synthesize and consume NAD in vertebrates. The abbreviations are defined in the text.
Electron transport chain in the mitochondrial intermembrane space
Salvage pathways use three precursors for NAD+.
Transmission electron micrograph of a chondrocyte, stained for calcium, showing its nucleus (N) and mitochondria (M).
Rossmann fold in part of the lactate dehydrogenase of Cryptosporidium parvum, showing NAD in red, beta sheets in yellow, and alpha helices in purple.
Typical mitochondrial network (green) in two human cells (HeLa cells)
In this diagram, the hydride acceptor C4 carbon is shown at the top. When the nicotinamide ring lies in the plane of the page with the carboxy-amide to the right, as shown, the hydride donor lies either "above" or "below" the plane of the page. If "above" hydride transfer is class A, if "below" hydride transfer is class B.
Model of the yeast multimeric tethering complex, ERMES
A simplified outline of redox metabolism, showing how NAD and NADH link the citric acid cycle and oxidative phosphorylation.
Evolution of MROs
The structure of cyclic ADP-ribose.
The circular 16,569 bp human mitochondrial genome encoding 37 genes, i.e., 28 on the H-strand and 9 on the L-strand.
Arthur Harden, co-discoverer of NAD

This is done by oxidizing the major products of glucose: pyruvate, and NADH, which are produced in the cytosol.

- Mitochondrion

In eukaryotes the electrons carried by the NADH that is produced in the cytoplasm are transferred into the mitochondrion (to reduce mitochondrial NAD) by mitochondrial shuttles, such as the malate-aspartate shuttle.

- Nicotinamide adenine dinucleotide
Two mitochondria from mammalian lung tissue displaying their matrix and membranes as shown by electron microscopy

11 related topics with Alpha

Overall

Overview of the citric acid cycle

Citric acid cycle

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Series of chemical reactions to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.

Series of chemical reactions to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.

Overview of the citric acid cycle
Structural diagram of acetyl-CoA: The portion in blue, on the left, is the acetyl group; the portion in black is coenzyme A.

In addition, the cycle provides precursors of certain amino acids, as well as the reducing agent NADH, that are used in numerous other reactions.

In eukaryotic cells, the citric acid cycle occurs in the matrix of the mitochondrion.

Interactive animation of the structure of ATP

Adenosine triphosphate

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Organic compound and hydrotrope that provides energy to drive many processes in living cells, such as muscle contraction, nerve impulse propagation, condensate dissolution, and chemical synthesis.

Organic compound and hydrotrope that provides energy to drive many processes in living cells, such as muscle contraction, nerve impulse propagation, condensate dissolution, and chemical synthesis.

Interactive animation of the structure of ATP
The cycles of synthesis and degradation of ATP; 2 and 1 represent input and output of energy, respectively.
This image shows a 360-degree rotation of a single, gas-phase magnesium-ATP chelate with a charge of −2. The anion was optimized at the UB3LYP/6-311++G(d,p) theoretical level and the atomic connectivity modified by the human optimizer to reflect the probable electronic structure.
An example of the Rossmann fold, a structural domain of a decarboxylase enzyme from the bacterium Staphylococcus epidermidis with a bound flavin mononucleotide cofactor.

ATP production by a non-photosynthetic aerobic eukaryote occurs mainly in the mitochondria, which comprise nearly 25% of the volume of a typical cell.

Two equivalents of NADH are also produced, which can be oxidized via the electron transport chain and result in the generation of additional ATP by ATP synthase.

Summary of aerobic respiration

Glycolysis

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Metabolic pathway that converts glucose , into pyruvic acid (CH3COCO2H).

Metabolic pathway that converts glucose , into pyruvic acid (CH3COCO2H).

Summary of aerobic respiration
Summary of the 10 reactions of the glycolysis pathway
Glycolysis pathway overview.
Eduard Buchner. Discovered cell-free fermentation.
Otto Meyerhof. One of the main scientists involved in completing the puzzle of glycolysis
Yeast hexokinase B
Bacillus stearothermophilus phosphofructokinase
Yeast pyruvate kinase

The free energy released in this process is used to form the high-energy molecules adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide (NADH).

When glucose has been converted into G6P by hexokinase or glucokinase, it can either be converted to glucose-1-phosphate (G1P) for conversion to glycogen, or it is alternatively converted by glycolysis to pyruvate, which enters the mitochondrion where it is converted into acetyl-CoA and then into citrate.

The electron transport chain in the cell is the site of oxidative phosphorylation. The NADH and succinate generated in the citric acid cycle are oxidized, releasing the energy of O2 to power the ATP synthase.

Oxidative phosphorylation

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Metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing chemical energy in order to produce adenosine triphosphate (ATP).

Metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing chemical energy in order to produce adenosine triphosphate (ATP).

The electron transport chain in the cell is the site of oxidative phosphorylation. The NADH and succinate generated in the citric acid cycle are oxidized, releasing the energy of O2 to power the ATP synthase.
Reduction of coenzyme Q from its ubiquinone form (Q) to the reduced ubiquinol form (QH2).
Complex I or NADH-Q oxidoreductase. The abbreviations are discussed in the text. In all diagrams of respiratory complexes in this article, the matrix is at the bottom, with the intermembrane space above.
Complex II: Succinate-Q oxidoreductase.
The two electron transfer steps in complex III: Q-cytochrome c oxidoreductase. After each step, Q (in the upper part of the figure) leaves the enzyme.
Complex IV: cytochrome c oxidase.
Mechanism of ATP synthase. ATP is shown in red, ADP and phosphate in pink and the rotating γ subunit in black.

In eukaryotes, this takes place inside mitochondria.

The energy stored in the chemical bonds of glucose is released by the cell in the citric acid cycle producing carbon dioxide, and the energetic electron donors NADH and FADH.

The electron transport chain in the mitochondrion is the site of oxidative phosphorylation in eukaryotes. The NADH and succinate generated in the citric acid cycle are oxidized, which releases the energy of oxygen to power ATP synthase.

Electron transport chain

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Series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples this electron transfer with the transfer of protons (H+ ions) across a membrane.

Series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples this electron transfer with the transfer of protons (H+ ions) across a membrane.

The electron transport chain in the mitochondrion is the site of oxidative phosphorylation in eukaryotes. The NADH and succinate generated in the citric acid cycle are oxidized, which releases the energy of oxygen to power ATP synthase.
Photosynthetic electron transport chain of the thylakoid membrane.
Depiction of ATP synthase, the site of oxidative phosphorylation to generate ATP.

The energy released by reactions of oxygen and reduced compounds such as cytochrome c and (indirectly) NADH and FADH is used by the electron transport chain to pump protons into the intermembrane space, generating the electrochemical gradient over the inner mitochondrial membrane.

Most eukaryotic cells have mitochondria, which produce ATP from reactions of oxygen with products of the citric acid cycle, fatty acid metabolism, and amino acid metabolism.

An ion gradient has potential energy and can be used to power chemical reactions when the ions pass through a channel (red).

Chemiosmosis

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Movement of ions across a semipermeable membrane bound structure, down their electrochemical gradient.

Movement of ions across a semipermeable membrane bound structure, down their electrochemical gradient.

An ion gradient has potential energy and can be used to power chemical reactions when the ions pass through a channel (red).
Chemiosmosis in a mitochondrion.
Energy conversion by the inner mitochondrial membrane and chemiosmotic coupling between the chemical energy of redox reactions in the respiratory chain and the oxidative phosphorylation catalysed by the ATP synthase.
Directions of chemiosmotic proton transfer in the mitochondrion, chloroplast and in gram-negative bacterial cells (cellular respiration and photosynthesis). The bacterial cell wall is omitted, gram-positive bacterial cells do not have outer membrane.
Chemiosmotic coupling between the energy of sunlight, bacteriorhodopsin and phosphorylation (chemical energy) during photosynthesis in halophilic bacteria Halobacterium salinarum (syn. H. halobium). The bacterial cell wall is omitted.
Early cell powered by external proton gradient near a deep-sea hydrothermal vent. As long as the membrane (or passive ion channels within it) is permeable to protons, the mechanism can function without ion pumps.

The generation of ATP by chemiosmosis occurs in mitochondria and chloroplasts, as well as in most bacteria and archaea.

The theory suggests essentially that most adenosine triphosphate (ATP) synthesis in respiring cells comes from the electrochemical gradient across the inner membranes of mitochondria by using the energy of NADH and FADH2 formed from the breaking down of energy-rich molecules such as glucose.

The enzyme glucosidase converts the sugar maltose into two glucose sugars. Active site residues in red, maltose substrate in black, and NAD cofactor in yellow.

Enzyme

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Enzymes are proteins that act as biological catalysts (biocatalysts).

Enzymes are proteins that act as biological catalysts (biocatalysts).

The enzyme glucosidase converts the sugar maltose into two glucose sugars. Active site residues in red, maltose substrate in black, and NAD cofactor in yellow.
Eduard Buchner
Enzyme activity initially increases with temperature (Q10 coefficient) until the enzyme's structure unfolds (denaturation), leading to an optimal rate of reaction at an intermediate temperature.
Organisation of enzyme structure and lysozyme example. Binding sites in blue, catalytic site in red and peptidoglycan substrate in black.
Enzyme changes shape by induced fit upon substrate binding to form enzyme-substrate complex. Hexokinase has a large induced fit motion that closes over the substrates adenosine triphosphate and xylose. Binding sites in blue, substrates in black and Mg2+ cofactor in yellow.
Chemical structure for thiamine pyrophosphate and protein structure of transketolase. Thiamine pyrophosphate cofactor in yellow and xylulose 5-phosphate substrate in black.
The energies of the stages of a chemical reaction. Uncatalysed (dashed line), substrates need a lot of activation energy to reach a transition state, which then decays into lower-energy products. When enzyme catalysed (solid line), the enzyme binds the substrates (ES), then stabilizes the transition state (ES‡) to reduce the activation energy required to produce products (EP) which are finally released.
The metabolic pathway of glycolysis releases energy by converting glucose to pyruvate via a series of intermediate metabolites. Each chemical modification (red box) is performed by a different enzyme.
In phenylalanine hydroxylase over 300 different mutations throughout the structure cause phenylketonuria. Phenylalanine substrate and tetrahydrobiopterin coenzyme in black, and Fe2+ cofactor in yellow.
Hereditary defects in enzymes are generally inherited in an autosomal fashion because there are more non-X chromosomes than X-chromosomes, and a recessive fashion because the enzymes from the unaffected genes are generally sufficient to prevent symptoms in carriers.

the hydride ion (H−), carried by NAD or NADP+

For example, fatty acids are synthesized by one set of enzymes in the cytosol, endoplasmic reticulum and Golgi and used by a different set of enzymes as a source of energy in the mitochondrion, through β-oxidation.

Schematic demonstrating mitochondrial fatty acid beta-oxidation and effects of long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency, LCHAD deficiency

Beta oxidation

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Schematic demonstrating mitochondrial fatty acid beta-oxidation and effects of long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency, LCHAD deficiency
Complete beta oxidation of linoleic acid (an unsaturated fatty acid).

In biochemistry and metabolism, beta-oxidation is the catabolic process by which fatty acid molecules are broken down in the cytosol in prokaryotes and in the mitochondria in eukaryotes to generate acetyl-CoA, which enters the citric acid cycle, and NADH and FADH2, which are co-enzymes used in the electron transport chain.

Simplified gluconeogenesis pathway (as occurs in humans). Acetyl-CoA derived from fatty acids (dotted lines) may be converted to pyruvate to a minor extent under conditions of fasting.

Gluconeogenesis

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Metabolic pathway that results in the generation of glucose from certain non-carbohydrate carbon substrates.

Metabolic pathway that results in the generation of glucose from certain non-carbohydrate carbon substrates.

Simplified gluconeogenesis pathway (as occurs in humans). Acetyl-CoA derived from fatty acids (dotted lines) may be converted to pyruvate to a minor extent under conditions of fasting.
Catabolism of proteinogenic amino acids. Amino acids are classified according to the abilities of their products to enter gluconeogenesis:
Gluconeogenesis pathway with key molecules and enzymes. Many steps are the opposite of those found in the glycolysis.

The location of the enzyme that links these two parts of gluconeogenesis by converting oxaloacetate to PEP – PEP carboxykinase (PEPCK) – is variable by species: it can be found entirely within the mitochondria, entirely within the cytosol, or dispersed evenly between the two, as it is in humans.

Oxaloacetate is reduced to malate using NADH, a step required for its transportation out of the mitochondria.

Illustration of the malate-aspartate shuttle pathway

Malate-aspartate shuttle

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Illustration of the malate-aspartate shuttle pathway

The malate-aspartate shuttle (sometimes simply the malate shuttle) is a biochemical system for translocating electrons produced during glycolysis across the semipermeable inner membrane of the mitochondrion for oxidative phosphorylation in eukaryotes.

The shuttle system is required because the mitochondrial inner membrane is impermeable to NADH, the primary reducing equivalent of the electron transport chain.