0:03 a constant source of blood glucose is an
0:05 absolute requirement for human life that
0:08 is why the body develop mechanisms for
0:11 storing a supply of glucose in a rapidly
0:14 mobilizable form namely glycogen these
0:16 mechanisms are glycogenesis the
0:18 conversion of glucose to glycogen for
0:21 storage and glycogenolysis the
0:23 conversion of glycogen back to glucose for
0:29 utilization let's first discuss
0:31 glycogenesis which is composed of four
0:35 steps step one the synthesis of uin
0:37 diphosphate glucose it is synthesized
0:40 from glucose 1 phosphate and urine
0:43 triphosphate acted upon by the enzyme
0:46 UDP glucose pyrophosphate forming now
0:49 your uin th phosphate
0:52 glucose step two synthesis of a primer
0:55 to initiate glycogen synthesis since
0:57 adding UDP glucose and other glucose
1:00 molecules to elongate the chain via
1:03 glycogen synthes cannot occur a primer
1:04 should be first
1:07 formed a protein called glycogenin can
1:09 serve as an acceptor of glucose residues
1:13 from UDP glucose glycogen in itself can
1:15 catalyze this reaction because it is an
1:17 enzyme just add few more molecules of
1:20 glucose from UDP glucose producing a
1:23 short alpha1 14 link glucos Cil chain
1:25 that can serve as a primer that is able
1:28 to be elongated by glycogen synthase
1:32 step three elongation of glycogen chains
1:34 you can now add molecules of glucose
1:37 from UDP glucose at the non-reducing end
1:39 to elongate the chain via glycogen
1:42 synthase it is the enzyme responsible
1:45 for making the alpha1 14 linkages in
1:49 glycogen step four formation of branches
1:50 the branches are made by the action of
1:54 the enzyme Amo alpha1 14 to Alpha one6
1:57 trans glucosidase it removes a set of 6
1:59 to8 glucos residues from the non
2:02 reducing end of the glycogen chain
2:05 breaking an alpha1 14 Bond and attaches
2:07 it to a non-terminal glucos residue by
2:11 an alpha one6 linkage resulting to a new
2:14 non-reducing end you can now repeat step
2:16 three and four to form a highly branched
2:19 polysaccharide named glycogen now let's
2:22 go to glycogenolysis which is composed
2:25 of Three Steps step one shortening of
2:29 chains the enzyme glycogen phosphor cves
2:31 alpha1 14 glycosidic bonds between
2:34 glucos Cil residues at non-reducing ends
2:36 until four glucos Cil units remain on
2:39 each chain before a branch point the
2:40 remaining structure is called limit
2:43 extreme and phosphor cannot degrade it
2:47 further step two removal of branches the
2:49 branches are removed by the debranching
2:52 enzyme first it removes the outer three
2:54 of the four glucosyl residues attached
2:58 at a branch next is it transfers them to
3:00 the non-reducing end of another chain
3:07 length the remaining glucose residue
3:10 attached in an alpha one6 linkage is
3:12 still removed by the debranching enzyme
3:14 releasing it as free
3:17 glucose this glucos Cil chain is now
3:20 available again for degradation via the
3:27 phosphor step three conversion of
3:29 glucose 1 phosphate to glucose 6 phosphate
3:30 phosphate
3:32 since the glucose released by glycogen
3:34 phosphor is still in the glucose one
3:37 phosphate form it has to be converted
3:57 phosphoglucomutase in the liver glucose
3:59 6 phosphate is transported into the the
4:02 endoplasmic reticulum by glucose 6 phosphate
4:03 phosphate
4:06 translocates here the glucose 6
4:08 phosphate is converted to glucose via
4:09 glucose 6
4:12 phosphatase hepatocytes release this
4:14 glycogen derived glucose into the blood
4:17 to help maintain blood glucose
4:21 levels however in the muscles glucose 6
4:23 phosphate cannot be sent into the blood
4:25 because of the lack in the enzyme glucos
4:28 6 phosphatase instead it enters
4:30 glycolysis providing The energy needed
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