Glycogen Metabolism | Glycogenolysis | Pathway, Enzymes and Regulation

Summary

This 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

• 🚀 Glycogen metabolism, or glycogenolysis, is the process of breaking down glycogen into glucose for energy.
• 🔍 Glycogen has a complex and branching structure, allowing for rapid release of glucose from multiple points.
• 🏋️ Glycogen serves as a rapid energy source during physical activity, particularly in muscles.
• 🍬 In the liver, glycogen is used to maintain blood glucose levels, especially during fasting and between meals.
• 🔬 Glycogenolysis begins with the enzyme glycogen phosphorylase, which targets the alpha 1-4 glycosidic bond of glycogen.
• 🛠️ The debranching enzyme plays a crucial role in glycogen metabolism by transferring residues and hydrolyzing alpha 1-6 bonds.
• ⚡ Glycogenolysis can generate energy anaerobically, without the need for oxygen.
• 🔄 Glycogen synthesis and breakdown are regulated by different enzymes and hormones, such as insulin and glucagon.
• 💊 Pyridoxal phosphate, a derivative of vitamin B6, is required by glycogen phosphorylase for its function.
• 🔄 Glycogen phosphorylase is activated by physical activity indicators like AMP and calcium in skeletal muscle.
• 🌟 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

00:00

🚀 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.

05:01

🔍 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.

10:02

👋 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.

Keywords

💡Glycogen Metabolism

Glycogen metabolism, also known as glycogenolysis, is the process of breaking down glycogen into glucose for energy. It is a central theme of the video, which discusses how glycogen is utilized as a rapid energy source. The script explains that glycogen metabolism has advantages such as being a rapid energy source and anaerobic generation, but also disadvantages like limited storage capacity.

💡Glycogen

Glycogen is a highly complex and branching structure made of glucose units. It serves as a storage form of glucose in the body, primarily in the liver and muscles. The script describes glycogen's structure as advantageous for rapid energy release due to the many points where glucose can be released.

💡Anaerobic Generation

Anaerobic generation refers to the process of producing energy without the need for oxygen. In the context of glycogen metabolism, the script mentions that energy from glycogen stores can be generated anaerobically, which is beneficial during high-intensity exercise or oxygen-deprived conditions.

💡ATP

ATP, or adenosine triphosphate, is the primary energy currency of cells. The script explains that glycogen metabolism generates 3 ATP per glucose from a glycogen molecule, as opposed to 2 ATP from non-glycogen glucose sources, highlighting the efficiency of glycogen as an energy source.

💡Glycogen Phosphorylase

Glycogen phosphorylase is an enzyme that plays a key role in glycogen metabolism by catalyzing the breakdown of glycogen into glucose-1-phosphate. The script details how this enzyme targets the alpha 1-4 glycosidic bond of glycogen and is regulated by various factors such as vitamin B6 and energy indicators.

💡Debranching Enzyme

The debranching enzyme is crucial for the complete breakdown of glycogen branches. It has dual functions as a transferase and a glucosidase, as explained in the script. It moves residues from one branch to another and hydrolyzes the alpha 1-6 bond at branch points, allowing glycogen phosphorylase to continue its action.

💡Phosphorylation

Phosphorylation is a biochemical process where a phosphate group is added to a protein, often affecting its activity. The script explains that phosphorylation activates glycogen phosphorylase and inhibits glycogen synthase, which are opposite effects and central to the regulation of glycogen metabolism.

💡Gluconeogenesis

Gluconeogenesis is the process by which glucose is synthesized from non-carbohydrate precursors. The script mentions that in the liver, glucose-6-phosphatase converts glucose-1-phosphate into glucose, which can then be used for gluconeogenesis, highlighting the liver's role in maintaining blood glucose levels.

💡Insulin

Insulin is a hormone that regulates blood sugar levels by promoting the storage of glucose as glycogen. The script explains that insulin activates glycogen synthase and inhibits glycogen phosphorylase, showing its role in promoting glycogen synthesis over breakdown.

💡Glucagon and Epinephrine

Glucagon and epinephrine are hormones that have opposing effects to insulin. The script describes how they inhibit glycogen synthase and activate glycogen phosphorylase, indicating their role in stimulating glycogen breakdown for energy release during stress or low blood sugar.

💡Calcium

Calcium is an important signaling molecule in cells, including muscle cells. The script notes that calcium activates glycogen phosphorylase in skeletal muscle, linking muscle contraction and physical activity to the breakdown of glycogen for energy production.

💡AMP

AMP, or adenosine monophosphate, is a molecule that indicates low energy levels in cells. The script explains that AMP activates glycogen phosphorylase in skeletal muscle, showing how the body responds to energy depletion by promoting glycogen breakdown.

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