CHAPTER 24 Glycogen Degradation

Most glycogen is found in muscle and liver cells Glycogen particles in a liver cell section

The enzyme Glycogen Phosphorylase -Catalyzes phosphorolysis – Cleavage of a bond by group transfer to an oxygen atom of phosphate -Glycogen phosphorylase removes glucose residues from the end of glycogen -Acts only on  -1  4 linkages of a glycogen polymer -The product is glucose 1-phosphate, which is converted to glucose 6-phosphate

Figure 24.2: The glycogen phosphorylase removes single glucose units via cleavage of  -1,4 glycosidic bonds.

Metabolism of Glucose 1-Phosphate Phosphoglucomutase catalyzes the conversion of glucose 1-phosphate to glucose 6-phosphate

Hormones Regulate Glycogen Metabolism -Insulin produced by  -cells of the pancreas in response to high blood glucose (the “fed” state) -Insulin increases the rate of glucose transport into muscle and adipose tissue via the glucose transporter (GLUT 4) -Glucagon is secreted by the  -cells of the pancreas in response to low blood glucose (the fasting state) -Glucagon stimulates glycogen degradation to restore blood glucose to steady-state levels -Epinephrine (adrenaline) is released from the adrenal glands in response to sudden energy requirements (“fight or flight”)

Hormones Regulate Glycogen Metabolism -Epinephrine and glucagon stimulates the breakdown of glycogen to glucose 1-phosphate

Figure 24.11: Signal transduction pathway activates glycogen phosphorylase Amplification via cyclic AMP