Pentose Phosphate Pathway
Pentose phosphate pathway is a major source of NADPH enzyme required for a wide range of anabolic processes. Generally, there are 3 phases of the processes and each, offers a distinct outcome. The metabolites of an outcome can be fed into different pathways depending on the needs of an organism.
Gluconeogenesis in the processes is usually connected to pentose phosphate pathways. If the need for the NADPH in the beginning of a metabolite in an anabolic process increases, there will be also an increase in a gluconeogenesis.
The introduction of pentose phosphate pathway
Glucose-6-phosphate is the main molecule in the body that is responsible for anabolic reactions. This is because of the structure of the molecule as it readily donates ions and more specifically hydrogen ions to the metabolites. As a result, it reduces them efficiently and makes them easily available for harvesting energy later on.
The pentose phosphate pathway however, is the main source for NADPH. It is also responsible for the production for Ribose-5-phosphate, a very important component of the nucleic acids. Pentose phosphate pathway can also produce glyceraldehyde 3 phosphate to allow for harvesting of energy in ETC and TCA cycles.
The enzymes that are highly responsible for catalyzing PPP processes are similarly found in abundant in the liver. This is the major site or organ in the body for gluconeogenesis and in the cytosol. The cytosol is however the place in which the synthesis of fatty acids takes place and is an NADPH dependent process.
There are different pentose phosphate pathway phases including oxidation phase, isomerization phase and rearrangement phase
The oxidation phase
Oxidation phase begins when PPH molecule is oxidized in the presence of G6PD and NADP. This is a crucial irreversible and highly regulated step because fatty acyl-CoA and NADPH are very strong negative inhibitors in the enzyme. The purpose of the reaction is to enhance production of NADPH is high and fatty acid synthesis is no longer needed.
The oxidation phase of PPP is responsible for the production of NADPH in all anabolic processes.
After oxidation, Isomerization of pentose phosphate pathway will occur. Ribulose 5 phosphate can be isomerized to produce ribose 5 phosphae by phosphopentose isomerase. The product is crucial because it is the main building block of nucleic acid.
If the production of ribose-5-phosphate exceeds the needed amount, phosphopentose epimerase will catalyze a rearrangement to produce different carbon chains. The length carbon chains will however have an array of metabolic fates.
The rearrangement phase of pentose phosphate pathway
Transaldolase and transketolase are two major enzymes that are required for rearrangement of PPP. The latter cleaves a two carbon unit from xyulose 5-p and adds 2 carbon units to ribose e5 phosphate to produce sedoheptulose 7-p and glyceraldehyde 3-p.
Transaldolase is responsible for cleaving carbon units from sedoheptulose 7-P and adds 3 carbon units to glyceraldehyde 3-P resulting in fructose 6 P and 4 -P.
The rearrangement phase ends with an array of length sugars that can be efficiently fed into metabolic processes. For instance, fructose 6-P is an active and key intermediate of glycolysis and glyceraldehyde 3-P.
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