What is Glycogen? The Important Take-home Message Ensure you are optimizing glycogen stores before exercise, maintaining it during exercise, and replenishing it after exercise. References Goodman, MN. Amino acid and protein metabolism. In Exercise, nutrition and energy metabolism, Eds. Gluconeogenesis is the process of synthesizing glucose from non-carbohydrate sources. The starting point of gluconeogenesis is pyruvic acid, although oxaloacetic acid and dihydroxyacetone phosphate also provide entry points.
Lactic acid, some amino acids from protein and glycerol from fat can be converted into glucose. Gluconeogenesis is similar but not the exact reverse of glycolysis, some of the steps are the identical in reverse direction and three of them are new ones.
Without going into detail, the general gluconeogenesis sequence is given in the graphic on the left. Notice that oxaloacetic acid is synthesized from pyruvic acid in the first step. Oxaloacetic acid is also the first compound to react with acetyl CoA in the citric acid cycle.
If the concentration of acetyl CoA is low and concentration of ATP is high then gluconeogenesis proceeds. Also notice that ATP is required for a biosynthesis sequence of gluconeogenesis. Gluconeogenesis occurs mainly in the liver with a small amount also occurring in the cortex of the kidney. Very little gluconeogenesis occurs in the brain, skeletal muscles, heart muscles or other body tissue.
In fact, these organs have a high demand for glucose. Therefore, gluconeogenesis is constantly occurring in the liver to maintain the glucose level in the blood to meet these demands. Link to Rodney Boyer - Gluconeogenesis -. Quiz: How many pyruvic acid molecules are required to make glucose? Answer Pyruvic acid has 3 carbons, glucose has 6 carbons, therefore 2 pyruvic acid molecules are needed. Summary of Metabolic Processes Metabolic Process Brief Description Starting Compound and End Product Energy Required or Given off glycogenolysis Answer s-glycogen e-glucose- 6-phosphate Answer neither glycogenesis Answer s-glucose- 6-phosphate e-glycogen Answer needed glycolysis aerobic Answer s-glucose- 6-phosphate e- pyruvic acid Answer given off gluconeogenesis Answer s-pyruvic acid e-glucose- 6-phosphate Answer needed Summary Questions:.
Carbohydrate Metabolism Overview. Citric Acid Cycle. Elmhurst College. Glycolysis Summary. Pyruvic Acid - Crossroads. Most of the carbohydrates we eat are converted to glucose, our main source of energy. When the body doesn't need fuel, the glucose molecules are linked together in chains of eight to 12 glucose units which form a glycogen molecule.
The main trigger for this process is insulin:. The amount of glycogen stored in these cells can vary depending on how active you are, how much energy you burn at rest , and the types of food you eat. Glycogen stored in muscle is primarily used by the muscles themselves, while those stored in the liver are distributed throughout the body—mainly to the brain and spinal cord.
Glycogen should not be confused with the hormone glucagon, which is also important in carbohydrate metabolism and blood glucose control. At any given time, there are about 4 grams of glucose in your blood.
When the level begins to decline—either because you have not eaten or are burning glucose during exercise—insulin levels will also drop. When this happens, an enzyme called glycogen phosphorylase starts breaking glycogen down to supply the body with glucose.
For the next eight to 12 hours, glucose derived from liver glycogen becomes the body's primary energy source. Your brain consumes more than half of the body's blood glucose during periods of inactivity. What you eat and how much you move around also influence glycogen production. The effects are especially acute if you're following a low-carb diet , where the primary source of glucose synthesis—carbohydrate—is suddenly restricted.
When first starting a low-carb diet, your body's glycogen stores can be severely depleted and you may experience symptoms like fatigue and mental dullness. Additionally, any amount of weight loss can have the same effect on glycogen stores. Initially, you may experience a rapid drop in weight. After a period of time, your weight may plateau and possibly even increase.
The phenomenon is partly due to the composition of glycogen, which is primarily water. In fact, the water in these molecules accounts for three to four times the weight of the glucose itself. As such, rapid depletion of glycogen at the onset of the diet triggers the loss of water weight. Over time, glycogen stores are renewed and the water weight begins to return. When this happens, weight loss may stall or plateau.
Gains experienced in the beginning come from water loss, not fat loss, and are only temporary. Fat loss can continue despite the short-term plateau effect.
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