The gluconeogenesis pathway seems quite pointless to me. I don't understand why an organism would want to spend energy to create a molecule that can then be metabolized again for less energy? The pathway seems only to serve as a complete waste of energy?
Can someone explain why we have gluconeogenesis and when it is used?
Answer
Gluconeogenesis is not the reversal of the glycolysis, but the generation of glucose from non-carbohydrate precursors (like odd chain fatty acids and proteins). The reason why we have this process is because some organs and tissues can only use glucose as their energy source. These include the brain (although ketone bodies can be used here as well), erythrocytes, testes and the kidney medulla.
Usually the glucose for the supply of these tissues comes directly from carbohydrates in food or storage carbohydrates as glycogen or starch, but when these are not available, the body has another way to get around this problem and to avoid the starvation of these tissues. See for example here and here.
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