The citric acid cycle —also known as the Krebs cycle, Szent-Györgyi-Krebs cycle or the TCA cycle (tricarboxylic acid cycle)—is a series of chemical reactions to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins. The Krebs cycle is used by organisms that respire (as opposed to organisms that ferment) to generate energy, either by anaerobic respiration or aerobic respiration. In addition, the cycle provides precursors of certain amino acids, as well as the reducing agent NADH, that are used in numerous other reactions. Its central importance to many biochemical pathways suggests that it was one of the earliest components of metabolism. Even though it is branded as a 'cycle', it is not necessary for metabolites to follow only one specific route; at least three alternative segments of the citric acid cycle have been recognized.
Glycolysis is the metabolic pathway that converts glucose into pyruvate, and in most organisms, occurs in the liquid part of cells, the cytosol. The free energy released in this process is used to form the high-energy molecules adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide (NADH). Glycolysis is a sequence of ten reactions catalyzed by enzymes.
A dehydrogenase is an enzyme belonging to the group of oxidoreductases that oxidizes a substrate by reducing an electron acceptor, usually NAD+/NADP+ or a flavin coenzyme such as FAD or FMN. Like all catalysts, they catalyze reverse as well as forward reactions, and in some cases this has physiological significance: for example, alcohol dehydrogenase catalyzes the oxidation of ethanol to acetaldehyde in animals, but in yeast it catalyzes the production of ethanol from acetaldehyde.
Nicotinamide adenine dinucleotide (NAD) is a coenzyme central to metabolism. Found in all living cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an adenine nucleobase and the other, nicotinamide. NAD exists in two forms: an oxidized and reduced form, abbreviated as NAD+ and NADH (H for hydrogen), respectively.
In biochemistry, an oxidoreductase is an enzyme that catalyzes the transfer of electrons from one molecule, the reductant, also called the electron donor, to another, the oxidant, also called the electron acceptor. This group of enzymes usually utilizes NADP+ or NAD+ as cofactors. Transmembrane oxidoreductases create electron transport chains in bacteria, chloroplasts and mitochondria, including respiratory complexes I, II and III. Some others can associate with biological membranes as peripheral membrane proteins or be anchored to the membranes through a single transmembrane helix.
In biochemistry and metabolism, beta oxidation (also β-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. It is named as such because the beta carbon of the fatty acid undergoes oxidation to a carbonyl group. Beta-oxidation is primarily facilitated by the mitochondrial trifunctional protein, an enzyme complex associated with the inner mitochondrial membrane, although very long chain fatty acids are oxidized in peroxisomes.
In enzymology, a vomifoliol dehydrogenase (EC 1.1.1.221) is an enzyme that catalyzes the chemical reaction
In enzymology, a cholest-5-ene-3β,7α-diol 3β-dehydrogenase (EC 1.1.1.181) is an enzyme that catalyzes the chemical reaction
In enzymology, a L-gulonate 3-dehydrogenase (EC 1.1.1.45) is an enzyme that catalyzes the chemical reaction
In enzymology, an omega-hydroxydecanoate dehydrogenase (EC 1.1.1.66) is an enzyme that catalyzes the chemical reaction
In enzymology, a sterol-4alpha-carboxylate 3-dehydrogenase (decarboxylating) (EC 1.1.1.170) is an enzyme that catalyzes the chemical reaction
In enzymology, a 3-hydroxy-2-methylbutyryl-CoA dehydrogenase (EC 1.1.1.178) is an enzyme that catalyzes the chemical reaction
In enzymology, a 3-hydroxyacyl-CoA dehydrogenase (EC 1.1.1.35) is an enzyme that catalyzes the chemical reaction
In enzymology, a (R)-2-hydroxyacid dehydrogenase (EC 1.1.1.272) is an enzyme that catalyzes the chemical reaction
In enzymology, a (R)-2-hydroxy-fatty-acid dehydrogenase (EC 1.1.1.98) is an enzyme that catalyzes the chemical reaction
In enzymology, a (S)-2-hydroxy-fatty-acid dehydrogenase (EC 1.1.1.99) is an enzyme that catalyzes the chemical reaction
In enzymology, a NADH peroxidase (EC 1.11.1.1) is an enzyme that catalyzes the chemical reaction
In enzymology, a 1-pyrroline-5-carboxylate dehydrogenase (EC 1.2.1.88) is an enzyme that catalyzes the chemical reaction
In enzymology, a pyrroline-5-carboxylate reductase (EC 1.5.1.2) is an enzyme that catalyzes the chemical reaction
In enzymology, a 4-hydroxy-tetrahydrodipicolinate reductase (EC 1.17.1.8) is an enzyme that catalyzes the chemical reaction
