Cellular metabolism and fermentation through glycolysis

Atom balance is maintained by the two phosphate Pi groups: For simple fermentationsthe metabolism of one molecule of glucose to two molecules of pyruvate has a net yield of two molecules of ATP. Cells performing aerobic respiration synthesize much more ATP, but not as part of glycolysis.

Cellular metabolism and fermentation through glycolysis

Catalytic Mechanism The enzyme does not require metal ions for its activity; one of the amino acids in the active site acts as a general base being able to abstract a hydride ion from the hydroxyl group bound to C1 of glucose 6-phosphate.

This causes glucose 6-phosphate, a cyclic hemiacetal with carbon 1 in the aldehyde oxidation state, to be oxidized to a cyclic ester, namely, a lactone. Because such histidine is conserved in many of the glucose 6-phosphate dehydrogenases sequenced, it is likely that this catalytic mechanism can be generalized to all glucose 6-phosphate dehydrogenases.

In humans, the enzyme exists in two forms: In fact, the binding of the oxidized coenzyme to a specific site close to the dimer interface, but distant from the active site, is required to maintain its dimeric conformation.

Under these conditions the oxidative phase is virtually inactive. Therefore it is possible to state that the fate of glucose 6-phosphate, an intermediate common to both glycolysis and the phosphogluconate pathway, also depends on the current needs for NADPH.

A second mechanism for the regulation of glucose 6-phosphate dehydrogenase activity calls into question the accumulation of acyl-CoAs, intermediates in fatty acid synthesis.

These molecules, by binding to the dimeric form of the enzyme, lead to dissociation into the constitutive monomers, and then to the loss of the catalytic activity. Insulin up-regulates the expression of the genes for glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase.

Therefore, in the well-fed state, the hormone increases carbon flow through the pentose phosphate pathway and then the production of NADPH. Insulin also promotes the synthesis of fatty acids.

However, in the cell this ring-opening reaction, an hydrolysis, is accelerated by the catalytic action of 6-phosphogluconolactonase EC 3. The reaction is catalyzed by 6-phosphogluconate dehydrogenase EC 1. It consists of an acid-base catalysis proceeding through a three step mechanism in which two strictly conserved residues, a lysine Lysand a glutamate Gluare involved; in humans, Lys and the Glu This leads to the formation of the 3-keto intermediate and a molecule of NADPH that leaves the active site.

In the second step, the decarboxylation step, 3-ketophosphogluconate, that is very susceptible to decarboxylation, is converted to the cis-1,2-enediol of ribulose 5-phosphate, a high energy intermediate.

What is the pentose phosphate pathway?

The result is the formation of ribulose 5-phosphate. An enediol is an organic compound containing two carbon atoms linked by a double bond and an hydroxyl group -OH bound to both carbon atoms. The enediol can have cis or trans configuration. Therefore, the oxidative phase of the pentose phosphate pathway ends with the production of ribulose 5-phosphate, namely, the substrate for the reactions of the non-oxidative phase.

The overall equation of the oxidative phase is: This phase begins with two reactions: Enzymatic isomerizations and epimerizations play an important role in carbohydrate metabolism. In isomerization reactions, the interchange of chemical groups occurs between carbon atoms.

This reaction is catalyzed by phosphopentose isomerase or ribose 5-phosphate isomerase EC 5.


The formation of the cis-1,2-enediol intermediate occurs via a proton-transfer mechanism common to the aldose-ketose isomerizations. The proposed catalytic mechanism for phosphopentose isomerase from E. Catalytic Mechanism In the first step, the furanose ring of the substrate is opened, opening induced by the interaction with an aspartic acid residue Asp81 that accepts a proton from the hydroxyl group bound to C-1, whereas it is likely that water is the proton donor.

Once the chain is opened, a glutamic acid residue Glu acts as a general base, as a nucleophile, abstracting a proton bound to the C-2, whereas Asp81 donates a proton. As a result, cis-1,2-enediol intermediate is produced.

During the synthesis of ribose 5-phosphate from ribulose 5-phosphate phosphopentose isomerase works in reverse.

Xylulose 5-phosphate is a regulatory molecule that inhibits gluconeogenesis and stimulates glycolysis by controlling the levels of fructose 2,6-bisphosphate in the liver.Oct 14,  · Glycolysis is a complex biological process that occurs to convert glucose into pyruvate in order to provide energy for each living cell.

Since the glycolysis cycle involves the conversion of blood sugar into an anion of pyruvic acid (pyruvate), glycolysis is also referred to as the citric acid cycle. Cellular respiration is a set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products.

Cellular metabolism and fermentation through glycolysis

Fermentation is the first stage of cellular respiration, glycolysis, plus reduction of the electron carrier NAD+. The term glycolysis describes exactly what is occurring during this metabolic step—the lysis, or breaking down, of the sugar glucose.

Endosymbiont theory for origin of mitochondria. The location of the electron transport chain on the inner mitochondrial membrane, and the pyruvate oxidation and citric acid cycle in the mitochondrial matrix, makes sense in light of the endosymbiont theory for the origin of mitochondria.

Cellular respiration is a set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products.

The reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy in the process, as weak so-called "high-energy. Metabolism (/ m ə ˈ t æ b ə l ɪ z ə m /, from Greek: μεταβολή metabolē, "change") is the set of life-sustaining chemical reactions in regardbouddhiste.com three main purposes of metabolism are the conversion of food/fuel to energy to run cellular processes, the conversion of food/fuel to building blocks for proteins, lipids, nucleic acids, and some carbohydrates, and the elimination of.

Glycolysis | Cellular respiration | Biology (article) | Khan Academy