glucose

Examples of glucose in the following topics:

• Hormonal Regulation of Metabolism

  • Insulin lowers blood glucose levels by enhancing the rate of glucose uptake and utilization by target cells, which use glucose for ATP production.
  • This prevents glucose from being absorbed by cells, causing high levels of blood glucose, or hyperglycemia (high sugar).
  • High blood glucose levels make it difficult for the kidneys to recover all the glucose from nascent urine, resulting in glucose being lost in urine.
  • As the levels of glucose in the blood rise, insulin stimulates the cells to take up more glucose and signals the liver to convert the excess glucose to glycogen, a form in which it can be stored for later use.
  • When the levels of glucose in the blood fall, glucagon responds by stimulating the breakdown of glycogen into glucose and signals the production of additional glucose from amino acids.

• Connecting Other Sugars to Glucose Metabolism

  • But living things consume more than glucose for food.
  • Glycogen, a polymer of glucose, is an energy-storage molecule in animals.
  • The glycogen is hydrolyzed into the glucose monomer, glucose-1-phosphate (G-1-P), if blood sugar levels drop.
  • The catabolism of sucrose breaks it down to monomers of glucose and fructose.
  • The entire globular granule may contain around 30,000 glucose units.

• Connecting Lipids to Glucose Metabolism

  • Lipids can be both made and broken down through parts of the glucose catabolism pathways.
  • Like sugars and amino acids, the catabolic pathways of lipids are also connected to the glucose catabolism pathways.
  • The lipids that are connected to the glucose pathways are cholesterol and triglycerides.
  • Thus, synthesis of cholesterol requires an intermediate of glucose metabolism.
  • Triglycerides can be both made and broken down through parts of the glucose catabolism pathways.

• Carbohydrate Molecules

  • Plants synthesize glucose using carbon dioxide and water, and glucose, in turn, is used for energy requirements for the plant.
  • Plants are able to synthesize glucose, and the excess glucose is stored as starch in different plant parts, including roots and seeds.
  • The cells can then absorb the glucose.
  • It is made up of monomers of glucose.
  • Whenever blood glucose levels decrease, glycogen is broken down to release glucose in a process known as glycogenolysis.

• Connecting Proteins to Glucose Metabolism

  • Excess amino acids are converted into molecules that can enter the pathways of glucose catabolism.
  • They can be broken down into their constituent amino acids and used at various steps of the pathway of glucose catabolism.
  • When deaminated, amino acids can enter the pathways of glucose metabolism as pyruvate, acetyl CoA, or several components of the citric acid cycle.
  • For example, deaminated asparagine and aspartate are converted into oxaloacetate and enter glucose catabolism in the citric acid cycle.
  • Several amino acids can enter glucose catabolism at multiple locations.

• Importance of Glycolysis

  • Glycolysis is the first step in the breakdown of glucose to extract energy for cellular metabolism.
  • Glucose enters heterotrophic cells in two ways.
  • These transporters assist in the facilitated diffusion of glucose.
  • Glycolysis is the first pathway used in the breakdown of glucose to extract energy.
  • Glycolysis is the first pathway of cellular respiration that oxidizes glucose molecules.

• Regulatory Mechanisms for Cellular Respiration

  • Cellular respiration can be controlled at each stage of glucose metabolism through various regulatory mechanisms.
  • As such, some type of control exists at each stage of glucose metabolism.
  • Access of glucose to the cell can be regulated using the GLUT proteins that transport glucose .
  • In addition, different forms of the GLUT protein control passage of glucose into the cells of specific tissues.
  • GLUT4 is a glucose transporter that is stored in vesicles.

• The Energy-Requiring Steps of Glycolysis

  • In the first half of glycolysis, energy in the form of two ATP molecules is required to transform glucose into two three-carbon molecules.
  • Hexokinase phosphorylates glucose using ATP as the source of the phosphate, producing glucose-6-phosphate, a more reactive form of glucose.
  • This reaction prevents the phosphorylated glucose molecule from continuing to interact with the GLUT proteins.
  • In the second step of glycolysis, an isomerase converts glucose-6-phosphate into one of its isomers, fructose-6-phosphate.
  • This is a type of end-product inhibition, since ATP is the end product of glucose catabolism.

• Catabolite Activator Protein (CAP): An Activator Regulator

  • For example, when glucose is scarce, E. coli bacteria can turn to other sugar sources for fuel.
  • When glucose levels drop, cyclic AMP (cAMP) begins to accumulate in the cell.
  • The cAMP molecule is a signaling molecule that is involved in glucose and energy metabolism in E. coli.
  • The CAP assists in production in the absence of glucose.
  • As glucose supplies become limited, cAMP levels increase.

• Food Energy and ATP

  • The primary source of energy for animals is carbohydrates, primarily glucose: the body's fuel.
  • The digestible carbohydrates in an animal's diet are converted to glucose molecules and into energy through a series of catabolic chemical reactions.
  • When the amount of ATP available is in excess of the body's requirements, the liver uses the excess ATP and excess glucose to produce molecules called glycogen (a polymeric form of glucose) that is stored in the liver and skeletal muscle cells.
  • When blood sugar drops, the liver releases glucose from stores of glycogen.
  • Skeletal muscle converts glycogen to glucose during intense exercise.