pentoosifosfaattivaihe

Pentoosifosfaattivaihe, also known as the pentose phosphate pathway or the hexose monophosphate shunt, is a metabolic pathway parallel to glycolysis. It plays a crucial role in cellular metabolism by generating NADPH and producing pentose sugars. The pathway begins with glucose-6-phosphate, an intermediate of glycolysis.

The pentose phosphate pathway has two main phases: the oxidative phase and the non-oxidative phase. The oxidative phase involves a series of irreversible reactions that produce NADPH and ribulose-5-phosphate. During this phase, glucose-6-phosphate is oxidized, and NADP+ is reduced to NADPH. NADPH is an essential reducing agent used in various biosynthetic processes, such as fatty acid synthesis and steroid synthesis, and in protecting cells from oxidative damage.

The non-oxidative phase consists of reversible reactions that interconvert various phosphorylated sugars, including ribose-5-phosphate, erythrose-4-phosphate, and fructose-6-phosphate. Ribose-5-phosphate, a key product of this phase, is essential for the synthesis of nucleotides, which are the building blocks of DNA and RNA. The non-oxidative phase also allows for the entry of pentose phosphates back into glycolysis, ensuring that carbon skeletons are efficiently utilized.

The pentose phosphate pathway is particularly important in tissues with high rates of reductive biosynthesis, such as the liver, adipose tissue, and adrenal cortex, as well as in red blood cells where it provides NADPH to combat oxidative stress. Disruption of this pathway can lead to various metabolic disorders.