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From Wikipedia

Glycogen

Glycogen is the molecule that functions as the secondary long-term energy storage in animal and fungal cells. It is made primarily by the liver and the muscles, but can also be made by glycogenesis within the brain and stomach.

Glycogen is the analogue of starch, a less branched glucose polymer in plants, and is commonly referred to as animal starch, having a similar structure to amylopectin. Glycogen is found in the form of granules in the cytosol in many cell types, and plays an important role in the glucose cycle. Glycogen forms an energy reserve that can be quickly mobilized to meet a sudden need for glucose, but one that is less compact than the energy reserves of triglycerides (lipids). In the liver hepatocytes, glycogen can compose up to 8% of the fresh weight (100–120 g in an adult) soon after a meal. Only the glycogen stored in the liver can be made accessible to other organs. In the muscles, glycogen is found in a low concentration (1% to 2% of the muscle mass). However, the amount of glycogen stored in the body, especially within the red blood cells, liver& muscles, mostly depends on physical training, basal metabolic rate and eating habits such as intermittent fasting. Small amounts of glycogen are found in the kidneys, and even smaller amounts in certain glial cells in the brain and white blood cells. The uterus also stores glycogen during pregnancy to nourish the embryo.

Function and regulation of liver glycogen

As a meal containing carbohydrates is eaten and digested, blood glucose levels rise, and the pancreas secretes insulin. Glucose from the portal vein enters livercells (hepatocytes). Insulin acts on the hepatocytes to stimulate the action of several enzymes, including glycogen synthase. Glucosemolecules are added to the chains of glycogen as long as both insulin and glucose remain plentiful. In this postprandial or "fed" state, the liver takes in more glucose from the blood than it releases.

After a meal has been digested and glucose levels begin to fall, insulin secretion is reduced, and glycogen synthesis stops. When it is needed for energy, glycogen is broken down and converted again to glucose. Glycogen phosphorylase is the primary enzyme of glycogen breakdown. For the next 8–12 hours, glucose derived from liver glycogen will be the primary source of blood glucose to be used by the rest of the body for fuel.

Glucagon is another hormone produced by the pancreas, which in many respects serves as a counter-signal to insulin. When the blood sugar begins to fall below normal, glucagon is secreted in increasing amounts. It stimulates glycogen breakdown into glucose even when insulin levels are abnormally high.

In muscle and other cells

Muscle cell glycogen appears to function as an immediate reserve source of available glucose for muscle cells. Other cells that contain small amounts use it locally as well. Muscle cells lack the enzyme glucose-6-phosphatase, which is required to pass glucose into the blood, so the glycogen they store is destined for internal use and is not shared with other cells. (This is in contrast to liver cells, which, on demand, readily do break down their stored glycogen into glucose and send it through the blood stream as fuel for the brain or muscles). Glycogen is also a suitable storage substance due to its insolubility in water, which means it does not affect the osmotistic levels and pressure of a cell.

Glycogen debt and endurance exercise

Long-distance athletes such as marathon runners, cross-country skiers, and cyclists often go into glycogen debt, where almost all of the athlete's glycogen stores are depleted after long periods of exertion without enough energy cons


From Yahoo Answers

Question:I always thought they were the same thing, like glycogen was the plural. I know glucose is a monosaccharide, but what about glycogen?

Answers:Glycogen is a polysaccharide, it is made up from many glucose molecules as a way of storing and transporting them en masse. An important thing to remember is that glycogen is soluble in the blood so it can move around the body. It is formed in the liver from glucose molecules in animals.

Question:Hi everyone, I'm completed a study guide for Biology, and ran into a few questions I don't understand. If you know the answer, please let me know! 2.) Where does gas exchange occur in plants and in animals? 3.) What does this equation represent? CO2 ---> C6H12O6 4.) What is the primary means by which plants obtain water from their environment? 5.) Why do plants have accessory pigments? 6.) What is the difference in hypertonic, hypotonic and isotonic and how does it relate to water movement in plants and animals? 7.) Name several processes that proceed spontaneously and several that require energy?

Answers:#4 Plants absorb water through their leaves. In vascular plants, water is absorbed through the "xylem". #6 Hypertonic cells are cells that have a higher concentration of solutes than their surrounding solution. This cause the water inside of the cell to go outward. This, in turn, causes the cell to shrivel up. Hypotonic is when more solute are in the solution which causes the water of the cell to leaves. This causes the water to go to an area of low concentration to an area of high concenteration which causes the cell to fill up with too much water. Isotonic is when everything is "just right"--not too much not too little..

Question:Which part of the day has the highest rate of metabolism?

Answers:Metabolism is essentially the speed at which our body's motor is running. The speed at which our body burns calories is called the metabolic rate. It's how fast your "motor" is running when you're still in a reclined position or sleeping. About 60-75% of energy is expended by the body at rest in such activities. The metabolism is based on the number of calories we burn throughout the day. Our body constantly burns calories to keep us going whether we are eating, sleeping, cleaning etc. People with a lower percentage of body fat (i.e. muscular) have a higher metabolism than others that are less muscular because muscle uses more calories to maintain itself than fat. Some people have a slower metabolic rate and have a harder time staying slim. Younger persons have higher (faster) metabolism because of the increased activity of cells. A slow metabolism actually causes to store fat. The slower the metabolic rate, the greater the weight gains. How to build muscles to improve metabolism? What type of exercise is ideal that speed up metabolism so that you burn calories even at rest or sleep? There are simple exercises that speed up the metabolism. Causes for Low Metabolism * Fasting * A low calorie diet * Snacking throughout the day on high sugared foods (candy, colas, cakes, gum). * Eating or drinking too much sugar containing foods. * Lack of physical activity. * Underactive thyroid. Metabolism Boosters There are some natural metabolism boosters (natural foods) that improves your metabolism. Do not take over the counter pills containing animal thyroid extract that claim to boost up metabolism. These products may have side effects as diarrhea, increased heart rate, excessive sweating, nervousness, tremors, bulging eyes, etc. How to Improve (Speed up) Metabolism * Do not skip any meals * Exercise daily * Build your muscles * Avoid alcohol, sugar, and fastings *Drink 8-10 glasses of water daily. *Eat foods with high nutrition values

Question:If lactic acid is produced during exercise, how can it be metabolized within the muscle?

Answers:It is transported to the liver which is the main site of metabolism to clear the lactic acid. Cori Cycle The Cori cycle refers to the metabolic pathway in which lactate produced by anaerobic glycolysis in the muscles moves via the blood stream to the liver where it it is converted to blood glucose and glycogen.

From Youtube

Glycogen Metabolism I :This course is part of a series taught by Kevin Ahern at Oregon State University on General Biochemistry. For more information about online courses go to ecampus.oregonstate.edu 1. The structure of glycogen consists of units of glucose linked in the alpha 1-4 configuration with branches linked in the 1-6 configuration. 2. Glycogen differs from starch in the amount of branching (much more). 3. Glycogen is a storage form of energy that can yield ATP very quickly, because glucose-1-phosphate can be released very quickly. 4. You should know the function/activites of the enzymes in glycogen breakdown - glycogen phosphorylase, phosphoglucomutase, and debranching enzyme. 5. Glycogen phosphorylase action on glycogen yields glucose-1-phosphate. Glycogen phosphorylase exists in two forms - phosphorylase a and phosphorylase b. Phosphorylase a differs from phosphorylase b only in that phosphorylase a contains two phosphates and phosphorylase b contains none. Phosphate is added to glycogen phosphorylase by the enzyme phosphorylase kinase. 6. Glucose-6-phosphate (G6P) has many different fates and sources. First, breakdown of glycogen produces G1P, which is readily converted to G6P. G6P can then go three different directions. In muscle and brain (and most other tissues), G6P enters glycolysis. In liver only, G6P enters gluconeogenesis and is converted to glucose for export to the bloodstream. In other tissues, G6P enters the pentose phosphate pathway and is oxidized to produce NADPH. 7 ...

Glycogen Metabolism II :This course is part of a series taught by Kevin Ahern at Oregon State University on General Biochemistry. For more information about online courses go to ecampus.oregonstate.edu In the notes below, I refer to Glycogen Phosphorylase a as GPa and Glycogen Phosphorylase b as GPb. I also refer to Glycogen Synthase a as GSa and Glycogen Synthase b as GSb. You are welcome to do the same. 1. Glycogen phosphorylase is present in two forms, GPa and GPb. They differ in phosphorylation. GPa is phosphorylated and GPb is not.1. GPb is converted into GPa by phosphorylation at two sites. Covalent modifications are DIFFERENT from allosteric controls, which interconvert the R and T states of BOTH GPa and GPb. 2. 9. Thus, the binding of epinephrine to the cell surface stimulates the following events in muscle relating to glycogen breakdown A. Epinephrine binds receptor B. Receptor activates a G protein to bind GTP C. Alpha subunit of G protein activates adenylate cyclase D. Adenylate cyclase catalyzes formation of cAMP E. cAMP activates protein kinase A F. Protein kinase A phosphorylates phosphorylase kinase, activating it. G. Phosphorylase kinase phosphorylates GPb, converting it to GPa H. GPa breaks down glycogen to yield G1P 10. Glycogen synthase, like glycogen phosphorylase, is regulated at least partially by phosphorylation. Note that GSa has NO PHOSPHATE whereas GSb HAS PHOSPHATE. You should know the function/activites of the enzymes in glycogen synthesis - phosphoglucomutase ...