Gluconeogenesis and the Calvin cycle

Published on April 19, 2020 Reviewed on November 27, 2022   40 min

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Greetings. Welcome to this Principles of Biochemistry lecture series. I am Jerry Feigenson, a professor in the Department of Molecular Biology and Genetics at Cornell University in the USA. Welcome to the 20th lecture. In the 19th lecture, you learned the possible fates of light energy after a photon is absorbed and you learned the roles of chlorophyll and other photosynthetic pigments. The events at the photosynthetic reaction centers create a gradient, mainly a gradient of protons across the thylakoid membrane. That gives rise to synthesis of ATP.
In this 20th lecture, we'll talk about metabolism of molecular synthesis and that's called anabolism. We will compare the anabolism of glucose synthesis, gluconeogenesis to glycolysis. We'll look briefly at the concept called 'substrate cycling'. Then we will look at the Calvin Cycle and the anabolic reactions of photosynthesis.
Now we'll talk about anabolism, biosynthesis. Until now, we've looked at metabolism that we call bioenergetics. How sugars, fats, amino acids, are oxidized to yield ATP. Then we looked at how the energy in sunlight produces ATP and NADPH. Now we'll talk about biosynthetic pathways and the pathways that we will study are those for synthesis of carbohydrates, then synthesis of lipids and finally, synthesis of nitrogen-containing molecules. We'll start with glucose synthesis, gluconeogenesis. Now you see some pictures here of glucose. But let me tell you some interesting facts about glucose. The brain and nerves use about 3/4 of the body's glucose. Brain and nerves do some gluconeogenesis, but no fat synthesis and they store essentially no fat. Red blood cells, actually, mature red blood cells. They only have a plasma membrane and they have cytosol and they store no fat. Mature red blood cells exclusively use glucose and glycolysis for energy needs. Skeletal muscle cells do store fat and do use glucose. We have enough glucose stored in our body as glycogen for about a half day's energy needs. So the body must continuously synthesize glucose. About 90% of all new glucose synthesis -gluconeogenesis - occurs in the liver. The other 10% occurs in kidney, muscles and nerves.