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Glycogen Metabolism

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Glycogen Metabolism Glycogen Function In liver The synthesis and breakdown of glycogen is regulated to maintain blood glucose levels. In muscle - The synthesis ... – PowerPoint PPT presentation

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Title: Glycogen Metabolism


1
Glycogen Metabolism
2
Glycogen Function
  • In liver The synthesis and breakdown of
    glycogen is regulated to maintain blood glucose
    levels.
  • In muscle - The synthesis and breakdown of
    glycogen is regulated to meet the energy
    requirements of the muscle cell.

3
Liver Cell
4
Glycogen structure
  • Large molecule
  • Branch points are frequent (about every fourth
    residue) allows glucose residues to be easily
    added or removed quicker than a linear molecule.

Glucose residues linked by a (1-4) glycosidic
bonds into chains chains branch via a (1-6)
linkage
5
  • Liver glycogen varies with food intake,
  • with a high level after a meal, and decreasing
    slowly as it is mobilized to maintain blood
    glucose levels. (see fig).

6
Glucose-6-phosphatase
phosphoglucomutase
phosphoglucomutase
G-1-phosphate uridylyl transferase
Glycogen synthases
7
Insulin
  • Peptide hormone of 51 aa produced in the pancreas
  • The stimulation of glycogen synthesis is one of
    the major physiological responses modulated by
    insulin
  • The exact mechanism by which insulin stimulates
    glycogen synthesis is not known
  • Insulin
  • Controls uptake and transport of glucose

8
Reciprocal Regulation of Glycogen Synthase and
Glycogen Phosphorylase
Glycogen Synthesis and Degradation are Highly
Regulated Pathways Glycogen synthase and
glycogen phosphorylase are the regulatory enzymes
of glycogen synthesis and degradation. Insulin
Induces and activates protein phosphatase-1
(removes p from GS- Activates GS Feeding results
in glycogen synthesis Glucagon activates Protein
kinase A which phosphorylates and inactivates
glycogen synthase and activates GP Little
glycogen synthesis during fasting. Lots of
breakdown
9
Effect of Hormone on Glycogen Metabolism
  • low blood glucose gt pancreas release glucagon
  • gtgtgtgtgtgtgt promotes glycogen degradation
  • During stress gt release epinephrine (adrenal
    medulla)
  • Promotes glucagon release gt increase blood
    glucose
  • interacts directly with both muscle and liver
    cells to promote glycogen degradation
  • High blood sugar gt release insulin (B-cells)
  • gtgtgtgtgt gt glycogen synthesis

10
Exercise and Glycogen Metabolism
  • Exercise of a muscle triggers mobilization of
    glycogen to form ATP.
  • The yield of ATP and the fate of carbons from
    glycogen depends on whether the muscles is
    white or red.
  • Red muscles are supplied with rich supply of
    blood, have a large amount of myoglobin, and are
    packed with mitochondria.

11
(No Transcript)
12
  • In red muscles glycogen is converted to
    pyruvate.
  • Then pyruvate is converted to CO2 and H2O ATP
  • (due to O2 and mitochondria).
  • White muscles have a poorer supply of O2 and
  • fewer mitochondria.
  • Glycogen -------gt Lactate primarily
  • White muscles have more capacity for
    glycogenolysis and glycolysis than red muscle
    fibers.

13
  • In Red muscles glycogen provides energy for
    longsustained activities. ( O2 mitochondria,
    more ATP)
  • In White muscles glycogen provides energy for
    short periods of maximal activity. (glycogen is
    mobilized rapidly)
  • In humans most skeletal muscles are a mixture of
    red and white fibers to provide for both rapid
    and sustained muscle activity.

14
McArdle's Disease
  • Glycogen phosphorylase deficient cannot break
    glycogen gt glucose
  • There is an abnormal accumulation of glycogen in
    muscle tissue.
  • Symptoms are exercise intolerance - muscular
    pain, fatigability - and muscle cramping. Rest
    relieves the muscle pain and enables exercise to
    resume

15
  • Muscle phosphorylase enzyme histochemistry in a
    control muscle shows the normal checkerboard
    staining pattern. Phosphorylase staining was
    absent in the patient's muscle

Assay Normal(nmol/min/g) Patient
Glycogen 0.1-1.5 1.85
Phosphorylase A 12.00 0.09
Phosphofructokinase 12.8 15.21
Myoadenylate deaminase 15.88 19.13

16
Study Questions
  • Whats the importance of glucose?
  • What is glucose stored as in the body? Where is
    it stored?
  • How much glycogen can be stored?
  • Whats the significance of glycogen being highly
    branched?
  • Is there any difference in the functions
    performed by the liver and muscle glycogen? If so
    what is it?
  • Define glycogenesis and glycogenolysis?
  • By the aid of diagrams explain the process of
    glycogenesis and glycogenolysis.
  • 9. Which hormones are involved in regulating
    these processes - glycogenesis and
    glycogenolysis?
  • 10. Why is it important that these processes
    are rigorously controlled?
  • How is blood glucose regulated?
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