0:01 hey everyone in this lesson we're
0:02 talking about glycogen synthesis also
0:04 known as glyco genesis so the first
0:06 thing we're gonna get into is what
0:08 glycogen is how it is actually
0:10 synthesized what are the enzymes
0:13 involved in glycogen synthesis then
0:15 we're gonna talk about where glycogen is
0:16 stored in the body and then finally
0:18 we're gonna talk about what the role of
0:23 glycogen is in our bodies so to begin
0:25 here is a picture demonstration of what
0:28 glycogen is actually actually looks like
0:31 and as you can see it's a very complex
0:36 branching structure with a core enzyme
0:37 and we'll get into what that core enzyme
0:41 is in a moment now glycogen if you break
0:43 down the word glycogen it's actually the
0:46 prefix glyco means glucose and then the
0:49 suffix Gen means producing so it's like
0:54 glucose producing now in fact like a gin
0:57 is simply just large polymer of glucose
1:01 monomers and glucose monomers can be
1:03 arranged in a linear fashion with
1:07 linkages of alpha one four linkages and
1:09 it is also a branching structure as I
1:11 mentioned before and the branch points
1:15 are actually alpha one six linkages now
1:18 the carbons are all numbered in a
1:22 glucose molecule and again as I
1:23 mentioned before the linear linkages are
1:28 1-4 and the branching is alpha one six
1:31 another important thing to note is that
1:34 glycogen has branching points at every
1:37 eight to twelve glucose monomers which
1:39 is important because it distinguishes
1:43 glycogen from similar compounds such as
1:47 amylopectin now glycogen because of the
1:50 word glucose producing it is in fact an
1:53 app it's or s-- of glucose and that's
1:56 the key about glycogen is actually a
1:58 rapid source of glucose and it is highly
2:00 important because it actually maintains
2:04 blood glucose levels and during
2:07 prolonged fasting glycogen stores in our
2:11 body typically only last about 1224
2:13 hours or a little less than 20
2:16 for hours now I mentioned before there's
2:21 a enzyme in the core of the glycogen now
2:25 this enzyme is called glycogenin and i
2:27 like to call this enzyme the catalytic
2:30 core and it's because it actually is an
2:33 initiating enzyme it itself begins the
2:35 process of glycogen synthesis and it
2:38 does it does this by actually Auto
2:41 glycosylated itself and it'll actually
2:44 produce or attach chains of about 10 to
2:47 20 glucose monomers to itself and that's
2:49 how this whole glycogen synthesis
2:55 process actually begins so stepping back
2:58 we start with a glucose now when a
3:03 glucose enters a cell it can actually be
3:06 foster elated by hexa kinase or gluco
3:08 kinase as we've learned before another
3:11 lessons to glucose 6-phosphate now I
3:13 always like to call glucose 6-phosphate
3:17 be the hub of many different signaling
3:20 pathways it in fact can be used for
3:25 several different purposes now the first
3:27 thing it can do is actually can go back
3:31 and be D phosphorylated to glucose by
3:33 glucose-6-phosphatase if glucose is
3:36 needed however it can also go into other
3:38 pathways one of them is that glucose
3:42 6-phosphate can be processed into glucan
3:45 or 1/5 lactone and then shunted into the
3:47 pentose phosphate pathway and if you
3:50 haven't watched that lesson please do so
3:53 because it's very important now another pathway
3:54 pathway
3:56 pretty much everybody's aware of is
3:59 glucose 6-phosphate can be processed to
4:02 fructose 6-phosphate and then used for
4:07 glycolysis for energy production and the
4:09 whole topic of this video though is that
4:11 if it's not used for any of these
4:15 pathways it can be used for glycogen
4:18 synthesis by being shunted or processed
4:21 into glucose 1-phosphate for glycogen
4:24 synthesis so if the glucose 6-phosphate
4:26 is used for glycogen synthesis
4:28 does that actually happen well the first
4:30 thing that happens is that
4:32 glucose-6-phosphate is action is acted
4:35 on by the enzyme phosphoglucomutase to
4:37 form glucose 1-phosphate
4:40 and pretty much this enzyme simply just
4:42 shifts the phosphate group from carbon 6
4:44 onto carbon 1 to form glucose 1-phosphate
4:45 1-phosphate
4:47 now it's important to realize that this
4:50 step is a reversible step which means
4:51 that glucose 1-phosphate
4:54 can be reprocessed into glucose
4:56 6-phosphate if the cell requires free
5:00 glucose and this is important during
5:02 glycogenolysis which i will talk about
5:04 in another video nevertheless if glucose
5:06 1-phosphate is going to be used for
5:08 glycogen synthesis what's the next step
5:11 well the next step is actually glucose
5:13 1-phosphate being acted on by UDP
5:15 glucose pyro phosphorylates now this is
5:20 a very important enzyme it takes UTP and
5:23 it activates glucose this is what we
5:27 call the activation step UTP will
5:31 actually attach a uridine moiety to the
5:34 glucose to form UDP glucose the active
5:37 form so once we have UDP glucose what is
5:39 the next step well the next step is
5:42 glycogen synthase now this isn't very
5:44 important enzyme and what it does is it
5:47 actually will remove the UDP portion off
5:50 of UDP glucose and add the glucose to
5:56 the actually a non-reducing end of a
5:59 glycogen chain so what it does is it'll
6:02 actually just pop the UDP portion off of
6:06 the UDP glucose and it will actually pop
6:10 the glucose monomer onto a non-reducing
6:15 end of a glycogen chain of glucose
6:18 monomers and it does this again in an
6:21 alpha 1 4 linkage it forms an alpha 1 4
6:28 linkage to actually extend the glycogen
6:30 chain and again the glucose is actually
6:34 added onto a non-reducing end so all the
6:37 other all the carbons besides carbon 1
6:40 are considered non-reducing but again it
6:42 is linked at an alpha one four linkage
6:46 so once we have a very long glycogen
6:48 chain where do the branching points come
6:51 from I mentioned glycogen synthase
6:56 attaches glucose to glucose at with
6:58 alpha one four linkage but I mentioned
7:00 before branching points are alpha one
7:03 six so how does that happen well if we
7:06 can imagine a glycogen chain very long
7:08 glycogen chain with a glycogen glycogen
7:12 in core how does the branching points or
7:13 where do the branching points come from
7:17 well simply there is something called a
7:19 branching enzyme now the branching
7:21 enzyme what it does is it'll actually
7:26 remove six to eight glucose molecules
7:28 off of the terminal end of the long
7:31 chain so what it'll do is it'll actually
7:35 chop off the last six to eight glucose
7:38 molecules off a long glycogen chain and
7:43 then it'll actually attach that chain it
7:46 chopped off back onto another chain of
7:49 glycogen with an alpha one six linkage
7:51 and that's how the branching enzyme
7:54 actually produces branch points so
7:57 that's where we get the very branching
8:02 structure of glycogen and this is also
8:05 very important to point out that with
8:09 the more branch points and the more free
8:11 terminal ends that glycogen actually has
8:15 it actually speeds up the rapid release
8:18 of glucose now instead of having in our
8:20 example instead of having one chain with
8:23 one free glucose at the end where one
8:25 can be removed at a time now we have two
8:27 points where two glucoses can be removed
8:30 at a time so it the branching of
8:33 glycogen actually speeds up the process
8:37 or it allows the cell to access more
8:39 glucose quicker and faster so that's why
8:43 it is actually a rapid source of glucose
8:45 now the final thing I want to talk about
8:49 is the UDP and UTP now I mentioned
8:52 before that UTP is used to activate glucose
8:53 glucose
9:00 and UDP UDP is actually removed off of
9:02 the udp-glucose once the glucose is
9:05 actually added to a glycogen chain so
9:10 that UDP glucose has to be recycled tea
9:13 back to UTP and it's done so by the
9:16 enzyme nucleoside diphosphate kinase and
9:21 this enzyme requires one ATP to reform
9:24 UTP so I just wanted to tell you guys
9:27 that just for sake of completeness so
9:29 we've talked about the production or the
9:30 synthesis of glycogen well we never
9:31 talked about where this is actually
9:36 happening where it's stored well as I
9:38 show you here the two major sites of
9:41 storage in our body for glycogen is the
9:45 liver and the muscle now with the liver
9:48 the glycogen is actually stored in the
9:53 cytoplasm of the hepatocytes and its
9:58 weight is about 100 grams and the role
10:01 of glycogen in the liver is pretty much
10:04 to maintain blood glucose levels that's
10:08 its main role when it's actually stored
10:12 and used in the liver and again it's
10:16 used during fasting and this is this
10:20 storage of or this reservoir of glycogen
10:24 usually only lasts for about 24 hours or
10:26 a little bit less than 24 hours and
10:29 again its main rule is just to maintain
10:33 blood glucose levels now with a muscle
10:36 again if glycogen is produced in the
10:40 muscle it's actually stored in the
10:45 cytoplasm of the muscle and in totality
10:49 in muscle glycogen will actually come
10:52 out to be about 400 grams of muscle mass
10:56 is actually glycogen and its role in the
10:58 muscle is actually an energy source and
11:02 it's actually utilized during exercise
11:04 so when you are exercising when you are
11:07 having acute periods of exercise
11:11 you begin to use muscle glycogen stores
11:16 and that is used simply before rapid and
11:19 glucose a rapid source of glucose and a
11:24 rapid source of energy anyways guys that
11:27 was a lesson on glycogen synthesis I
11:29 hope you found this video helpful if you
11:31 did please like and subscribe for more
11:32 videos like this one and as always thank
11:33 you so much for watching and have a
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