Glycogen Metabolism | Glycogenolysis | Pathway, Enzymes and Regulation
Summary
TLDRThis educational video delves into glycogen metabolism, also known as glycogenolysis, exploring how it serves as a rapid energy source due to its highly branched structure. It highlights the advantages, such as anaerobic energy generation and higher ATP yield per glucose molecule compared to non-glycogen sources. However, the script also addresses the limitations, including low ATP generation per mass and limited storage capacity. The lesson explains the enzymatic processes involved in glycogen breakdown and synthesis, emphasizing the role of glycogen phosphorylase and debranching enzyme. It further discusses the regulatory mechanisms by hormones like insulin, glucagon, and epinephrine, and how glycogenolysis differs in the liver for maintaining blood glucose levels and in skeletal muscle for energy during physical activity. The video concludes by explaining why glycogen-derived glucose yields 3 ATP instead of 2, providing a clear and concise overview of glycogen metabolism.
Takeaways
- π Glycogen metabolism, or glycogenolysis, is the process of breaking down glycogen into glucose for energy.
- π Glycogen has a complex and branching structure, allowing for rapid release of glucose from multiple points.
- ποΈ Glycogen serves as a rapid energy source during physical activity, particularly in muscles.
- π¬ In the liver, glycogen is used to maintain blood glucose levels, especially during fasting and between meals.
- π¬ Glycogenolysis begins with the enzyme glycogen phosphorylase, which targets the alpha 1-4 glycosidic bond of glycogen.
- π οΈ The debranching enzyme plays a crucial role in glycogen metabolism by transferring residues and hydrolyzing alpha 1-6 bonds.
- β‘ Glycogenolysis can generate energy anaerobically, without the need for oxygen.
- π Glycogen synthesis and breakdown are regulated by different enzymes and hormones, such as insulin and glucagon.
- π Pyridoxal phosphate, a derivative of vitamin B6, is required by glycogen phosphorylase for its function.
- π Glycogen phosphorylase is activated by physical activity indicators like AMP and calcium in skeletal muscle.
- π Glycogenolysis yields 3 ATP per glucose, compared to 2 ATP from non-glycogen glucose sources, due to the pre-phosphorylated state of glucose 1-phosphate.
Q & A
What is glycogen metabolism, also known as?
-Glycogen metabolism is also known as glycogenolysis, which is the process of breaking down glycogen and utilizing it.
Why is glycogen considered a rapid energy source?
-Glycogen is considered a rapid energy source because of its highly branched structure, which allows for the release of glucose at many points, making it quickly accessible for energy production.
How is energy generated from glycogen stores?
-Energy from glycogen stores is generated anaerobically, meaning it does not require oxygen.
Why does glycogenolysis generate more ATP per glucose compared to non-glycogen glucose sources?
-Glycogenolysis generates 3 ATP per glucose because the glucose released from glycogen is already in the form of glucose 1-phosphate, skipping the initial phosphorylation step that consumes 1 ATP in non-glycogen glucose sources.
What are some disadvantages of glycogenolysis?
-Disadvantages of glycogenolysis include its limited storage capacity and the fact that it can only generate a low amount of ATP per mass of glycogen due to its water-absorbing properties and carbohydrate nature.
What is the primary role of glycogen in muscle tissue?
-In muscle tissue, glycogen serves as a rapid source of energy during exercise or physical activity.
How is glycogen used in the liver?
-In the liver, glycogen is used to maintain blood glucose levels, which is important during fasting and between meals.
What enzyme initiates glycogenolysis and what does it do?
-Glycogen phosphorylase initiates glycogenolysis by targeting a free end of glycogen and releasing glucose 1-phosphate from an alpha 1-4 glycosidic bond.
How does the debranching enzyme assist in glycogen metabolism?
-The debranching enzyme assists in glycogen metabolism by acting as a transferase, moving three residues from a branch to another branch, and as a glucosidase, hydrolyzing the alpha 1-6 bond at branch points.
What are the regulatory differences between glycogen synthase and glycogen phosphorylase?
-Phosphorylation activates glycogen phosphorylase, while it inhibits glycogen synthase. Insulin activates glycogen synthase and inhibits glycogen phosphorylase, whereas glucagon and epinephrine have the opposite effects.
How does the regulation of glycogen metabolism differ between the liver and skeletal muscle?
-In the liver, glucose 6-phosphate is processed for gluconeogenesis, while in skeletal muscle, it is used for glycolysis. Additionally, calcium and AMP are activators of glycogen phosphorylase in skeletal muscle, which is specific to muscle activity.
Outlines
π Glycogen Metabolism: Breakdown and Utilization
This paragraph introduces glycogen metabolism, also known as glycogenolysis, as the focus of the lesson. It contrasts glycogen synthesis, previously discussed, with the current topic of how glycogen is broken down and used. The advantages of glycogenolysis are highlighted, such as its rapid energy release due to the highly branched structure of glycogen, its anaerobic energy generation, and the higher ATP yield per glucose molecule compared to non-glycogen sources. Disadvantages include the limited ATP generated per mass of glycogen due to its water absorption and the limited storage capacity that typically lasts about 24 hours. The paragraph also explains the different roles of glycogen in muscle and liver tissues and begins to describe the biochemical process of glycogenolysis, starting with the enzyme glycogen phosphorylase.
π Glycogenolysis Regulation and Metabolic Roles
This section delves deeper into the regulation of glycogen metabolism, focusing on the enzymes glycogen phosphorylase and glycogen synthase. It explains the role of insulin and glucagon in activating and inhibiting these enzymes, respectively, and how phosphorylation affects their activity. The paragraph also discusses the specific regulatory mechanisms in liver and skeletal muscle, detailing how glycogen phosphorylase is inhibited by energy indicators like ATP and glucose-6-phosphate, while glycogen synthase is activated by glucose-6-phosphate. The unique role of calcium and AMP in activating glycogen phosphorylase in skeletal muscle is highlighted, along with the different metabolic fates of glucose-6-phosphate in liver (gluconeogenesis) and skeletal muscle (glycolysis). The paragraph concludes by explaining why glycogen-derived glucose yields 3 ATP instead of 2, due to the pre-phosphorylated state of glucose-6-phosphate.
π Conclusion of Glycogen Metabolism Lesson
The final paragraph wraps up the lesson on glycogen metabolism with a brief recap and a call to action for the viewers. It encourages viewers to like and subscribe for more educational content, expressing gratitude for their engagement and wishing them well. This closing segment serves as a polite and positive conclusion to the informative session on glycogenolysis.
Mindmap
Keywords
π‘Glycogen Metabolism
π‘Glycogen
π‘Anaerobic Generation
π‘ATP
π‘Glycogen Phosphorylase
π‘Debranching Enzyme
π‘Phosphorylation
π‘Gluconeogenesis
π‘Insulin
π‘Glucagon and Epinephrine
π‘Calcium
π‘AMP
Highlights
Glycogen metabolism, also known as glycogenolysis, is discussed in the lesson.
Glycogen is a highly complex and branching structure.
Glycogenolysis can be used as a rapid energy source due to its highly branched structure.
Glycogen energy can be generated anaerobically without the need for oxygen.
Glycogenolysis generates 3 ATP per glucose from glycogen molecule compared to 2 ATP from non-glycogen glucose source.
Disadvantage: Low amount of ATP generated per mass of glycogen due to its water absorption and mass.
Glycogenolysis has a limited storage capacity and typically lasts about 24 hours.
Glycogen has separate roles in muscle and liver: muscle for energy during exercise and liver for maintaining blood glucose levels.
Glycogenolysis begins with the enzyme glycogen phosphorylase, which requires pyridoxal phosphate.
Glycogen phosphorylase targets alpha 1-4 glycosidic bonds and releases glucose 1-phosphate.
Debranching enzyme is used to metabolize glycogen by transferring residues and hydrolyzing alpha 1-6 bonds.
Glycogen phosphorylase and glycogen synthase oppose each other in the regulation of glycogen metabolism.
Insulin activates glycogen synthase and inhibits glycogen phosphorylase.
Glucagon and epinephrine inhibit glycogen synthase and activate glycogen phosphorylase.
Glycogen phosphorylase is inhibited by energy indicators such as ATP, glucose-6-phosphate, and glucose.
Glucose 6-phosphate activates glycogen synthase in the liver and skeletal muscle.
Calcium and AMP activate glycogen phosphorylase in skeletal muscle during physical activity.
Glucose 1-phosphate is converted to glucose 6-phosphate and then to glucose in the liver for gluconeogenesis.
In skeletal muscle, glucose 6-phosphate is used for glycolysis to produce energy.
Glycogenolysis generates 3 ATP per glucose molecule due to pre-phosphorylated glucose 6-phosphate.
Transcripts
hey everyone in this lesson we're
talking about glycogen metabolism also
known as glycogenolysis so in a previous
lesson we've talked about glycogen
synthesis and how its produced now and
this says we're going to talk about how
it's broken down and utilized and we're
also going to talk about the advantages
in disadvantages of glycogen metabolism
so as a reminder here is what glycogen
actually looks like as you remember it's
a highly complex and branching structure
and because of it one of the main
advantages of glycogenolysis is that it
can be used as a rapid energy source and
that's because it is highly branched its
has a lot of points where a glucose can
be released now another advantage is
that it is anaerobically generated the
energy from a glycogen store can be
actually generated anaerobically we do
not need oxygen and another advantage is
that it actually generates 3 ATP per
glucose from a glycogen molecule whereas
only 2 ATP are generated from a non
glycogen glucose source and I'll explain
to you why that is in a moment now
there's some of the disadvantages of
glycogen horses is that only a low
amount of ATP can be generated per mass
of glycogen and that's because glycogen
because it's a carbohydrate it absorbs a
lot of water it has a lot of mass as
opposed to something like adipose tissue
which is anhydrous so we cannot generate
a large amount of ATP for the size of
glycogen and another disadvantage of
glycogenolysis is that it is a limited
storage capacity in it typically only
lasts about 24 hours so glycogen has
separate roles depending on the tissue
it's utilized in in muscle it is used as
a rapid source of energy during exercise
or physical activity glycogen is used as
an energy source in the muscle but in
the liver glycogen is actually used to
maintain blood glucose levels and this
is important during fasting and also be
during the periods between meals so how
does glycogenolysis or glycogen
metabolism begin well it begins with the
enzyme glycogen phosphorylase and
glycogen phosphorylase is one of them
any enzymes that require pyridoxal
phosphate which is a derivative of
vitamin b6
now what glycogen phosphorylase does is
it targets a free end of glycogen and it
does it by actually targeting an alpha
1-4 glycosidic bond and in the process
it releases a glucose 1-phosphate so
glycogen phosphorylase will keep
removing a glucose 1-phosphate from a
branch of glycogen but one of the key
characteristics of glycogen
phosphorylase is that it actually stops
within 4 residues of a branch point due
to size and steric hindrance of the
enzyme so that means that the glycogen
phosphorylase cannot keep removing
residues off of a glycogen branch so how
does the cell continue to metabolize the
glycogen well it continues to metabolize
a glycogen by utilizing another enzyme
the debranching enzyme and the deep
wrenching enzyme has a couple of
functions one it acts as a transferase
so the debranching enzyme will move
three residues from a branch one branch
and move it to the free end of another
branch so that would help to reduce the
steric hindrance on the glycogen
phosphorylase however the debranching
enzyme also has another function and it
functions as a glue cassaday's to
hydrolyze in alpha one six bond a
branching point because as you remember
the glycogen phosphorylase can only act
on an alpha 1-4 glycosidic bond so the B
branching enzyme can take care of the
branch points on a glycogen and
hydrolyze an alpha 1 6 bond and when it
does hydrolyze enough one six Bond the
glucose or the residue released from the
glycogen is actually released as a free
glucose not a glucose 1-phosphate so
that is one important point to remember
so as we've learned glycogen can be
processed back into glucose 1-phosphate
by the enzyme glycogen phosphorylase and
as we've learned in a previous lesson
the glucose 1-phosphate can be used to
produce glycogen with the help of
glycogen synthase so how do these two
enzymes oppose each other and how do the
regulations differ on these enzymes well
the first thing is that insulin is
an activator of glycogen synthase
through another protein phosphatase
which we won't get into here but just
remember that insulin will actually
activate glycogen synthase now glucagon
and epinephrine will actually inhibit
glycogen synthase through protein kinase
a and this is through phosphorylation
mechanism so glucagon and epinephrine
lead to the phosphorylation and
inhibition of glycogen synthase NPK can
also inhibit glycogen synthase with
through phosphorylation as well now the
difference with regulation on oxygen
synthase as opposed to glycogen
phosphorylase is that insulin actually
inhibits glycogen phosphorylase through
a protein phosphatase as well but it's
the opposite with Glick gun and
epinephrine Gugu and epinephrine will
actually activate a phosphorylase kinase
to phosphorylate inactivate glycogen
phosphorylase so the important point to
get out of this is that phosphorylation
activates glycogen phosphorylase whereas
phosphorylation inhibits glycogen
synthase and an easy way to remember
this is that phosphorylation activates
phosphorylase phosphorylation
phosphorylase so hopefully that helps so
the two main areas in the body that
utilize glycogen are the liver and
skeletal muscle and we've learned some
of the regulation on glycogen metabolism
in the previous slide but I'm gonna get
into a little more detail in these
slides and how the regulation on
glycogen differs between the liver and
skeletal muscle so as we've learned
before glycogen phosphorylase can
process glycogen residues into glucose
1-phosphate
and glucose 1-phosphate can be utilized
to form glycogen with the enzyme
glycogen synthase and which direction
that goes and depends on regulation
within the cell and with glycogen
phosphorylase glycogen phosphorylase is
inhibited by indicators of energy such
as ATP it's also inhibited by
glucose-6-phosphate and it's inhibited
by glucose
anything that shows the cell that there
does not need to be any breakdown of
glycogen will actually stop
the process of glycogen phosphorylase
now the opposite in glycogen synthase is
glucose 6-phosphate will actually
activate glycogen synthase so glucose
6-phosphate will inhibit the
phosphorylase but it will activate the
synthase so in a liver hepatocyte when
the cell decides that it requires
glycogenolysis and produces glucose
1-phosphate
the glucose 1-phosphate will actually be
processed by the enzyme
phosphoglucomutase back into glucose
6-phosphate and then the glucose
6-phosphate will then be processed by
the enzyme glucose-6-phosphatase to
produce glucose in gluconeogenesis
so this production of glucose for
gluconeogenesis only occurs in the liver
due to glucose-6-phosphatase enzyme
which is only present in the liver it is
present a little bit in the kidneys but
majority is present in the liver now in
skeletal muscle it's the same thing as
we've seen before but the regulation is
slightly different with glycogen
synthase it's the same glucose
6-phosphate will activate glycogen
synthase to reroute glucose 1-phosphate
into glycogen storage now for glycogen
phosphorylase it's the same for ATP ATP
will inhibit glycogen phosphorylase the
glucose 6-phosphate will also inhibit
glycogen phosphorylase but there are a
couple additional regulators on this
enzyme in skeletal muscle one of them is
calcium calcium will actually activate
glycogen phosphorylase so you can think
about if you're exercising and
contracting your muscles you're getting
an influx of calcium calcium will then
actually activate glycogen phosphorylase
so that you start to break down your
glycogen stores and then another
activator of glycogen phosphorylase is a
MP and a MP is another indicator of
physical activity as you burn through
your ATP stores you produce a MP which
then will activate glycogen
phosphorylase to produce more glucose
1-phosphate
now glucose 1-phosphate once you have
glucose 1-phosphate will then produce
glucose 6-phosphate with the enzyme
phosphoglucomutase
but the difference between skull and
mouse on the liver is that the glucose
6-phosphate be
glycolysis to produce energy as opposed
to gluconeogenesis in the liver so
that's why you see the dual roles of
glycogenolysis in glycogen utilization
in these two tissues the liver in the
skeletal muscle so another point I want
to mention is that 3 ATP are generated
for every glucose from a glycogen as
opposed to non glycogen glucose and the
reason is is because when you actually
process a residue of glycogen we end up
getting the product glucose 6-phosphate
which is already phosphorylated so in a
normal cell when we bring glucose into
the cell the cell actually has to
phosphorylate the glucose into glucose
6-phosphate which actually costs one ATP
whereas with glycogen this is already
done that's already been phosphorylated
so we've actually invested that ATP
already previously and now when we bring
it back at a storage you actually get
more ATP when you bring glucose out of
storage from glycogen it is actually
already phosphorylated and it's already
glucose 6-phosphate which means it does
not need to be phosphorylated saving the
cell 1 ATP so that's why we actually get
an extra ATP 3 ATP as opposed to 2 ATP
anyways guys I hope you found this
lesson helpful if you did please like
and subscribe for more videos like this
one and as always thank you so much for
watching and have a great day
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