{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

chapter15 - CHAPTER 15 GLYCOGEN METABOLISM AND...

Info icon This preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Glucose Glucose 6-phosphate Fructose 6-phosphate Glyceraldehyde 3-phosphate Pyruvate Glycogen (glucose) n Ribose 5-phosphate CHAPTER 15 - GLYCOGEN METABOLISM AND GLUCONEOGENESIS Introduction Certain tissues, such as the brain and red blood cells, rely on glucose for fuel. Serum glucose levels must be maintained at about 5 mM. Serum glucose is maintained by dietary sources, glycogen breakdown, and synthesis from noncarbohydrate precursors via gluconeogenesis (see Figure 1). Glucose is polymerized to glycogen (animal starch) to avoid osmotic imbalances and stored primarily in the muscle and liver. Muscle tissue maintains a store of glycogen for its own use. The liver stores glycogen stores glycogen and breaks it down to glucose for export to other tissues. Notice in the scheme below that glycogen metabolism intersects glycolysis at glucose-6-phosphate. Keep in mind that, since glycogen is stored in a muscle cell for use only in that cell, glucose-6-phosphate is never hydrolyzed to glucose in muscle cells since once glucose is formed it can leave the cell (glucose-6-phosphate cannot leave the cell). Glycogen breakdown can be thought of as a mini-pathway that intersects glycolysis at glucose-6- phosphate. As is typically the case, there is a complementary, biosynthetic pathway that links the same endpoints. As is also typical, some of the enzymes are utilized by both catabolic and biosynthetic pathways, but at one point at the minimum, different enzymes are employed.
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon