viernes, 17 de abril de 2009

Pentose Phosphate Pathway

Pentose Phosphate Pathway

In most animal tissues, glucose is catabolized via de glycolityc pathway into two moleucles of pyruvate. pyruvate is then oxidizen via de citric acid cycle to generate ATP. There is another metabolic fato for glucose used to generate NADPH and specialized products needed by the cell. this pathway is called the pentose phosphate pathway. Some texto books call it the hexose monophosphate shunt, still others call it the phosphogluconate pathway. We will call it this time as the pentose phosphate pathway.

The pentose phosphate pathway produces NADPH whick is the universal reductant in anabolic pathways. in mammals the tissues requiring large amounts of NADPH produced by this pathway are the tissues than synthesize farry acids and steroids such as the mammary gland, adipose tissue, adrenal cortex and the liver. Tissues less active in fatty acidy synthesis such as skeletal muscle are virtually laching the pentose phosphate pathway.

The second function of the pentose phosphate pathway is to generate pentoses, particulary ribose which is necessary for the synthesisi of nucleic acids. It is convenient to think of the pentose phosphate pathway as operatingo in two phases. The first phase is the oxidative phase. Two of the first three reactions of the first phase generate NADPH. The second phase is the nonoxidative phase.
In the first step glucose-6-phosphate is oxidized into ribulose-5-phosphate, COx. during the oxidation of glucose-6-phosphate NADP is reduced into NADPH.
The second step of the phathway converts the ribulose-5-phosphate into other pentose-5-phosphates including ribose-5-phosphate used to synthesize nucleic acids.

The thirdstep includes a series of reactions that convert three of the pentose-5-phosphate so the cycle can be repeated. The direction of the pathway varies to meet different metabolic conditions.

Oxidative Phase

In this phase two molecules of NADP are reduced to NADPH using energy of the convertion of glucose-6-phosphate in ribulose-5-phosphate. The NADPH used in the sinthesize of cholesterol, hidrolization reactions of neurotransmiters.

Non oxidative phase

Up to ribulose-5-phosphate sintesizes xululose-5-phosphate and ribulose-5-phosphate.

Tailoring the pentose phosphate pathway to meet specific needs of the cell.
1). if the cell requires both ribose-5-P and NADPH
2).More ribose-5-P needed than NADPH.
3). More NADPH needen than Ribose-5-P
4). Both NADPH and ATP are needed but not ribose-5-P

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