Glycogen is the principal storage form of glucose in animal cells. In humans, the most glycogen is found in the liver (10% of the liver mass), whereas muscles only contain a relatively low amount of glycogen (1% of the muscle mass). In addition, small amounts of glycogen are found in certain glial cells in the brain.
Sometimes called “animal starch” for its resemblance with starch found in plants, it is stored in liver and muscle cells and can be converted to glucose if needed. In the liver this conversion is regulated by the hormone glucagon. Under certain conditions, between meals for instance, liver glycogen is an important source of blood glucose. Muscle cell glycogen appears to be only for local use. Glycogen is the primary glucose (energy) storage mechanism. It is stored in the form of granules in the cytosol which is where glycolysis takes place. These granules contain both glycogen and the necessary enzymes for its conversion into glucose.
Glycogen is a highly branched glucose polymer. It is formed of small chains of 8 to 12 glucose molecules linked together with &alpha (1�4) bonds. These small chains are in turn linked together with &alpha (1�6) bonds. A single molecule of glycogen can be made of up to 120,000 molecules of glucose. It is generated from glucose by the enzyme glycogen synthase. This process is called glycogenesis. The addition of a glucose molecule to glycogen takes two high energy bonds: one from ATP and one from UTP. Its breakdown into glucose, called glycogenolysis, is mediated by the enzyme glycogen phosphorylase. It’s highly branched.
Glycogen is a quick storage vehicle for the body to keep large amounts of glucose when it is not needed by the body. It is classed as a polysaccharide. Although much like amylopectin, glycogen contains more branched chains and has a higher molecular weight. It is stored in both the liver and muscles, but the liver store is more readily available for energy and blood sugar level maintenance, while the muscle store is mostly used for muscle fuel.
Glycogen stores of readily available glucose to supply the tissues with an oxidizable energy source are found principally in the liver, as glycogen. A second major source of stored glucose is the glycogen of skeletal muscle. However, muscle glycogen is not generally available to other tissues, because muscle lacks the enzyme glucose-6-phosphatase.
The major site of daily glucose consumption (75%) is the brain via aerobic pathways. Most of the remainder is utilized by erythrocytes, skeletal muscle, and heart muscle. The body obtains glucose either directly from the diet or from amino acids and lactate via gluconeogenesis. Glucose obtained from these two primary sources either remains soluble in the body fluids or is stored in a polymeric form, glycogen. Glycogen is considered the principal storage form of glucose and is found mainly in liver and muscle, with kidney and intestines adding minor storage sites. With up to 10% of its weight as glycogen, the liver has the highest specific content of any body tissue. Muscle has a much lower amount of glycogen per unit mass of tissue, but since the total mass of muscle is so much greater than that of liver, total glycogen stored in muscle is about twice that of liver. Stores of glycogen in the liver are considered the main buffer of blood glucose levels.
A) milk and cheese.
B) fruits and honey.
C) fruits and vegetables.
D) breads and cereals.
A) cause obesity.
B) promote tooth decay.
C) cause diabetes mellitus.
D) cause hyperactivity.
A) High blood pressure
B) High HDL cholesterol
C) Elevated glucose
D) Elevated triglycerides
D) Sugar cane
A) Carbohydrate digestion is assisted by cooking, which softens tough skins.
B) Carbohydrate digestion begins in the stomach.
C) Chewing food does not assist in carbohydrate digestion.
D) Saliva production does not influence starch digestion.
A) Salivary amylase
C) Pancreatic proteases
D) Pancreatic amylase
A) an enzyme that digests protein.
B) a branched chain of glucose units.
C) an enzyme that digests starch.
D) a straight chain of glucose units.
A) Starch to lactose to galactose
B) Starch to maltose to glucose
C) Starch to glycogen to glucose
D) Starch to sucrose to fructose
A) a milk allergy.
B) lactase deficiency.
C) milk bacteria.
D) intestinal bacteria.
A) gas, abdominal pain, and distention.
B) a rash, sneezing, and stuffy nose.
C) a headache and chest pain.
D) nausea and vomiting.
A) serve as raw material to build tissue.
B) work with enzymes to carry out chemical reactions.
C) repair tissue.
D) supply energy.
A) the liver to break down glycogen and release glucose into the blood.
B) muscle and fat cells to increase glucose uptake.
C) fat breakdown in fat tissue.
D) the liver to make glycogen from protein.
A) carbohydrate consumed.
B) glucose absorbed.
C) insulin released from the pancreas.
D) glycogen stored.
A) a long, straight glucose chain.
B) branched glucose chains.
C) a long, straight fatty acid chain.
D) branched amino acid chains
A) muscles and liver.
B) kidney and muscles.
C) liver and kidney.
D) liver and pancreas.
A) They are mostly polysaccharides.
B) The bonds between sugar units cannot be broken by human digestive enzymes.
C) They cannot be absorbed by the small intestine.
D) They are absorbed in the large intestine.
A) increase stool size significantly.
B) are not readily fermented by intestinal bacteria.
C) do not dissolve in water.
D) can lower blood cholesterol.
A) 10 to 12
B) 15 to 30
C) 20 to 34
D) 25 to 38
A) Eating enriched grains such as Rice Krispies and Saltines
B) Increasing his meat intake
C) Reading the labels of grain products and buying those labeled "wheat flour"
D) Eating more fruits and vegetables and not removing the edible peels
A) Kidney beans
B) English muffins made with enriched flour
C) Orange juice
D) Corn flakes
A) restrict fluid intake.
B) not be concerned about consuming large amounts.
C) avoid foods that are not whole grain.
D) increase fluid intake.
A) Grapefruit half, 2 fried eggs, 3 bacon slices, 1 slice of toast with butter, coffee
B) 8 ounces orange juice, 2 cups Cream of Wheat with 2 tablespoons sugar, English muffin with jelly, 1 cup whole milk
C) 8 ounces orange juice, 2 bran muffins, 8 ounces nonfat yogurt, coffee
D) 1 cup whole milk, 2 ounces sausage, 2 fried eggs, 1 slice of toast with butter
A) Type 1 diabetes, coronary artery disease, and cancer.
B) Type 1 diabetes, coronary artery disease, and stroke.
C) Type 2 diabetes, coronary artery disease, and stroke.
D) Type 2 diabetes, coronary artery disease, and cancer.
A) arises most commonly in adulthood.
B) caused by insensitivity of fat and muscle cells to insulin.
C) often associated with obesity.
D) the least common form of diabetes.
A) lose body fat.
B) eat regular meals.
C) maintain a constant ratio of carbohydrate to protein to fat throughout the day.
D) avoid sugar.
A) two monosaccharides.
B) two polysaccharides.
C) one monosaccharide and one polysaccharide.
D) two oligosaccharides.
a. raises blood cholesterol levels
b. speeds up transit time for food through the digestive system
c. causes diverticulosis
d. causes constipation
a. enzyme amylase
b. monosaccharide glucose
c. hormone insulin
d. hormone glucagon
a. indigestible fiber
b. simple carbohydrate
c. energy-yielding nutrient
d. animal polysaccharide
a. glucose, lactose
b. glucose, fructose
c. sucrose, maltose
d. fructose, sucrose
a. complex carbohydrate
c. simple carbohydrate
a. fresh fruits
b. fish and poultry
d. whole grains and cereals
e. both a and d
a. type 1
b. type 2
c. type 3
a. drinking high-fat milk
b. eating a large amount of yogurt
c. low lactase activity
d. a high-fiber diet
a. high body weight
b. high waist circumference
c. low blood sugar
d. low blood pressure
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