They serve as a source of both energy and chemical groups in biosynthetic reactions.
ATP (Adenosine Triphosphate).
NAD+ acts as an oxidizing agent in catabolism, while NADPH acts as a reducing agent in anabolism.
The high-energy thioester bond in acetyl CoA releases a large amount of free energy when hydrolyzed, allowing the acetate molecule to be readily transferred to other molecules.
ΔG° = – RT ln K
ΔG = 0 at equilibrium.
They link the breakdown of food molecules (catabolism) to the energy-requiring biosynthesis of small and large organic molecules (anabolism).
ΔG° = –5.94 log K
K = [X]/[Y], where [X] is the concentration of the product and [Y] is the concentration of the reactant at equilibrium.
Enzymes couple an energetically favorable reaction, such as the oxidation of foodstuffs, to an energetically unfavorable reaction, such as the generation of an activated carrier molecule.
An energy input from nucleoside triphosphate hydrolysis.
Pumps that transport substances into and out of the cell, and molecular motors that enable muscle cells to contract and nerve cells to transport materials.
Between –46 and –54 kJ/mole.
Provided that a suitable reaction path is available.
At equilibrium, there is no net change in the ratio of Y to X, and the ΔG for both forward and backward reactions is zero.
NADPH participates in many important biosynthetic reactions that would otherwise be energetically unfavorable.
Because they convert an energy-rich phosphoanhydride bond in ATP to a phosphoester bond, resulting in a large negative ΔG.
It must be coupled to a highly energetically favorable reaction to occur.
The hydrolysis of the terminal phosphate of ATP yields between 46 and 54 kJ/mole of usable energy.
The synthesis of biological polymers is driven by ATP hydrolysis.
Enzymes.
NADPH is a much stronger electron donor (reducing agent) than NADH, while NAD+ is a much better electron acceptor (oxidizing agent) than NADP+.
Through enzyme-catalyzed pathways where the –OH group is first activated by forming a high-energy linkage to a second molecule.
ATP is synthesized by coupling a highly energetically favorable reaction to an energetically unfavorable phosphorylation reaction in which a phosphate group is added to ADP.
The principle of coupled chemical reactions.
The intrinsic character of the molecules, as expressed in the value of ΔG° in kilojoules per mole.
It makes available a total free-energy change of about –100 kJ/mole.
Because the actual mechanisms linking ATP hydrolysis to their synthesis are more complex and do not leave phosphate groups in the final products.
Acetyl CoA transfers two-carbon acetyl groups.
The synthesis of the amino acid glutamine.
Carboxylated biotin transfers carboxyl groups in biosynthetic reactions, such as the production of oxaloacetate.
The activated intermediate (A–O–PO3) reacts with B–H to form the product A–B, releasing inorganic phosphate.
To create and maintain order within themselves to survive and grow.
Because the transfer of the hydride ion from NADPH is accompanied by a large negative free-energy change.
NADPH is primarily involved in anabolic reactions, while NADH plays a special role as an intermediate in the catabolic system of reactions that generate ATP through the oxidation of food molecules.
Activated carriers store energy in an easily exchangeable form and serve as a source of both energy and chemical groups in biosynthetic reactions.
ATP, NADH, and NADPH.
Condensation reaction, where a water molecule is lost.
NAD+ (nicotinamide adenine dinucleotide) and NADP+ (nicotinamide adenine dinucleotide phosphate) are important electron carriers in cells.
ATP acts as a convenient and versatile store of energy used to drive a wide variety of chemical reactions in cells.
The forward and backward fluxes of reacting molecules are equal and opposite at chemical equilibrium.
It produces heat only.
A phosphoanhydride bond.
K = [C][D] / [A][B]
Polymer-end activation and direct-monomer activation.
The reactive bond required for the condensation reaction.
Direct-monomer activation.
Because the total ΔG° for the series of sequential reactions has a large negative value.
Pyruvate carboxylase uses carboxylated biotin to transfer a carboxyl group to pyruvate, forming oxaloacetate.
Coenzyme A carries a readily transferable acetyl group in a thioester linkage, known as acetyl CoA, which is used to add two carbon units in the biosynthesis of larger molecules.
ΔG becomes less negative as the concentration of products increases and the concentration of substrates decreases.
The nucleotide derivative, usually adenosine diphosphate, serves as a convenient 'handle' for the recognition of the carrier molecule by specific enzymes, and may be a relic from an early stage of evolution.
By transferring its terminal phosphate to another molecule.
One high-energy intermediate.
NADPH acts as a reducing agent, transferring a hydride ion to reduce the C=C bond in the final stage of cholesterol biosynthesis.
It converts A–OH to a higher-energy intermediate compound, which then reacts with B–H to form A–B.
They carry hydride ions (H-), which consist of a proton (H+) plus two electrons.
ATP is hydrolyzed to ADP and inorganic phosphate, releasing energy that can be used to drive energetically unfavorable reactions.
ATP transfers phosphate groups and provides energy for biosynthesis and other cellular processes.
The equilibrium constant changes by a factor of 10.
By coupling it to a second reaction, analogous to the synthesis of activated carrier molecules.
ATP hydrolysis drives the reaction by producing a favorable free-energy change (ΔG° of –30.5 kJ/mole), which is larger in magnitude than the energy required for the synthesis of glutamine from glutamic acid plus NH3 (ΔG° of +14.2 kJ/mole).
Activated carrier molecules are generated in reactions coupled to ATP hydrolysis.
ATP transfers a phosphate group to A–OH to produce a high-energy intermediate, A–O–PO3.
They store energy as chemical-bond energy and carry it from sites of energy release to where it is needed for biosynthesis.
The synthesis of carboxylated biotin requires energy derived from ATP.
NADPH has an extra phosphate group compared to NADH, which gives it a slightly different shape and allows it to bind to different sets of enzymes.
The free-energy change (ΔG) must be less than zero for a reaction to proceed spontaneously.
Rocks falling from a cliff.
ΔG° = –2.58 ln K
They become NADH and NADPH, respectively.
The conversion of X to Y requires a more energetic collision, making it occur less often than the conversion of Y to X.
They provide the energy required to activate each subunit before its addition to the growing polymer chain.
Because the hydrolysis of these phosphoanhydride linkages releases a great deal of free energy.
The synthesis of nucleic acids (polynucleotides) from nucleoside triphosphates.
The –OH group involved in the condensation reaction is first activated by forming a high-energy linkage to a second molecule.
The net result is the formation of the product A–B from substrates A–OH and B–H, accompanied by the release of inorganic phosphate.
Polymer-end activation.
NADPH is an important carrier of electrons, produced in reactions where two hydrogen atoms are removed from a substrate. It holds its hydride ion in a high-energy linkage, making it an effective donor of its hydride ion to other molecules.
They are assembled from small activated precursor molecules by repetitive condensation reactions driven by ATP hydrolysis.
Water is added, breaking down the polymers in an energetically favorable reaction.
A–OH + ATP + B–H → A–B + ADP + phosphate.
NADPH is produced when two hydrogen atoms are removed from a substrate molecule, with both electrons and one hydrogen atom added to NADP+ to form NADPH, while the second hydrogen atom is released as a proton (H+).
NADPH and FADH2 transfer electrons and hydrogen atoms.
The removal of unfavorable repulsion between adjacent negative charges and the stabilization of the inorganic phosphate ion by resonance and hydrogen-bond formation with water.
ΔG° = –5.94 log ([C][D] / [A][B])
The overall free-energy change for a set of coupled reactions is the sum of the free-energy changes in each of its component steps.
The ΔG° for the coupled reaction will be –8 kJ/mole.
A condensation reaction links monomers together to form macromolecules, releasing water in the process.
NADPH operates chiefly with enzymes that catalyze anabolic reactions, supplying the high-energy electrons needed to synthesize energy-rich biological molecules.
The ratio of NAD+ to NADH is kept high, whereas the ratio of NADP+ to NADPH is kept low, allowing the cell to adjust the supply of electrons for different purposes.
The electromagnetic radiation of the Sun drives the formation of organic molecules in photosynthetic organisms.
Animals obtain their energy by eating organic molecules and oxidizing them in a series of enzyme-catalyzed reactions that are coupled to the formation of ATP.
ATP is used to form reactive phosphorylated intermediates, making the energetically unfavorable reaction of biosynthesis energetically favorable.
The high-energy intermediate, a nucleoside triphosphate, reacts with the growing end of an RNA or DNA chain, leading to the release of pyrophosphate.
The nicotinamide ring in NADP+ accepts the hydride ion (H-) to form NADPH.
Different pathways allow for independent regulation, enabling the cell to adjust the supply of electrons for the contrasting purposes of anabolic and catabolic reactions.
Polymer-end activation and direct-monomer activation.
The hydrolysis of pyrophosphate to inorganic phosphate is highly favorable and helps drive the overall reaction.
It is driven by ATP hydrolysis, where a nucleoside monophosphate is activated by the sequential transfer of terminal phosphate groups from two ATP molecules.
