Glycogen Metabolism - Intro

Question 1

What is glucose and how is it degraded?

Answer 1

A major metabolic fuel source degraded via glycolysis to produce ATP

Question 2

How do higher organisms protect themselves from potential fuel shortages?

Answer 2

By polymerizing excess glucose for storage as high molecular mass glucans (glucose polysaccharides) that may be readily metabolized in times of metabolic need

Question 3

What is the glucose storage substance in plans?

Answer 3

Starch, a mixture of the alpha(1–>4) linked glucan alpha-amylose and amylopectin, which has alpha(1–>6) branches every 24 to 30 residues

Question 4

What is the glucose storage substance in animals?

Answer 4

Glycogen, which differs from amylopectin only in that its branches occur every 8 to 14 residues

Question 5

Glycogen occurs in 100- to 400-Angstrom what?

Answer 5

Cytoplasmic granules

Question 6

What do glycogen granules contain?

Answer 6

• 120,000 glucose units
• Enzymes that catalyze glycogen synthesis and degradation
• Some of the enzymes that regulate these processes

Question 7

Where is glycogen most prominent?

Answer 7

In cells that make the greatest use of glycogen
- Muscle cells: maximally 1-2% glycogen by weight
- Liver cells: maximally 10% glycogen by weight, an approx.12 hr energy supply for the body

Question 8

How are glycogen’s glucose units mobilized?

Answer 8

By their sequential removal from the glucan chain’s nonreducing ends

Question 9

What are nonreducing ends?

Answer 9

Ends lacking a C1 -OH group

Question 10

Why is glycogen’s highly branched structure physiologically significant?

Answer 10

It permits glycogen’s rapid degradation through the simultaneous release of the glucose units at the end of every branch
- More free enzymes to be catabolized to glucose
- More soluble
More reducing ends

Question 11

Why does the body go to such metabolic effort to use glycogen for energy storage when fat, which is far more abundant in the body, seemingly serves the same purpose?

Answer 11

1) Muscles cannot mobilize fat as rapidly as they can glycogen
2) The fatty acid residues of fat cannot be metabolized anaerobically
3) Animals cannot convert fatty acids to glucose, so fat metabolism alone cannot adequately maintain essential blood glucose levels
4) Osmolarity of cells is not affected