Lipoprotein metabolism and transport | Chylomicron, VLDL,IDL, LDL,HDL | Metabolism | Biochemistry

Summary

This video delves into the world of lipoproteins, cholesterol transport, and metabolism. It introduces the various lipoproteins, including chylomicrons, VLDL, IDL, LDL, and HDL, highlighting their unique compositions and functions. The script explains the synthesis and metabolism of these particles, emphasizing the role of apolipoproteins and the impact of LDL in cardiovascular health. It also describes HDL as the 'good cholesterol' that helps remove excess cholesterol from arteries, contrasting it with LDL, the 'bad cholesterol.' The video promises a deeper exploration of these topics in future episodes.

Takeaways

• 🧬 Lipoproteins are complexes of lipids and proteins, including cholesterol, triglycerides, and phospholipids, with specific proteins like apolipoproteins.
• 🚀 There are five main types of lipoproteins: chylomicrons, VLDL (Very Low Density Lipoprotein), IDL (Intermediate Density Lipoprotein), LDL (Low Density Lipoprotein), and HDL (High Density Lipoprotein).
• 📚 VLDL is characterized by its high triglyceride content, while LDL is known for its high cholesterol content, making it a risk factor for heart disease.
• 🔬 HDL is rich in apolipoproteins, which aids in the transport of cholesterol from tissues back to the liver, earning it the nickname 'good cholesterol'.
• 🍔 Chylomicrons are synthesized in the intestine and are responsible for transporting dietary fats, primarily triglycerides, from the intestine to the bloodstream.
• 🏗️ VLDL is produced by the liver and is involved in the transport of endogenous triglycerides and cholesterol to peripheral tissues.
• 🛠️ Lipoprotein lipase, an enzyme found in adipose tissue, breaks down triglycerides in chylomicrons and VLDL into free fatty acids for storage.
• 🔄 The metabolism of lipoproteins involves a series of transformations, such as VLDL losing triglycerides to become IDL, which can further transform into LDL.
• 🛑 LDL can be harmful when it deposits cholesterol in artery walls, leading to atherosclerosis and increasing the risk of heart disease.
• 🔧 HDL helps prevent heart disease by picking up excess cholesterol from tissues and transporting it back to the liver for excretion or reuse.
• 📈 Understanding the roles and metabolism of different lipoproteins is crucial for managing lipid profiles and preventing cardiovascular diseases.

Q & A

What is a lipoprotein and what are its main components?

A lipoprotein is a complex particle consisting of both lipids and proteins. Its main components include cholesterol, triglycerides, phospholipids, and proteins known as apolipoproteins.

What are the different types of lipoproteins mentioned in the script, and what do their abbreviations stand for?

The script mentions five types of lipoproteins: Chylomicrons, VLDL (Very Low Density Lipoprotein), IDL (Intermediate Density Lipoprotein), LDL (Low Density Lipoprotein), and HDL (High Density Lipoprotein).

What is the primary function of chylomicrons?

The primary function of chylomicrons is to transport dietary lipids, mainly triglycerides, from the intestine to other parts of the body, particularly adipose tissue for storage.

How does the composition of chylomicrons differ from VLDLs?

Chylomicrons contain apolipoproteins C, B-48, and E, whereas VLDLs contain apolipoprotein B-100, C, and E. Chylomicrons are also enriched with triglycerides from the diet, while VLDLs are synthesized de novo in the liver.

What is the role of lipoprotein lipase in the metabolism of chylomicrons and VLDLs?

Lipoprotein lipase is an enzyme that breaks down triglycerides in chylomicrons and VLDLs into free fatty acids and glycerol. These free fatty acids are then stored in adipose tissue, while the remaining particles continue their metabolic pathways.

How does the liver synthesize and secrete VLDL?

The liver synthesizes VLDL by combining glycolysis-derived glycerol, free fatty acids from the cytosol, and cholesterol from the smooth endoplasmic reticulum. The VLDL particles, containing apolipoprotein B-100, are then packaged in the Golgi bodies and released into the bloodstream.

What is the significance of the LDL receptor and its interaction with apolipoprotein B-100?

The LDL receptor on liver hepatocytes recognizes apolipoprotein B-100 on LDL particles, facilitating receptor-mediated endocytosis. This process allows the liver to take up and recycle cholesterol from LDL particles as needed.

What is the primary function of HDL, and why is it considered 'good cholesterol'?

HDL's primary function is to pick up excess cholesterol from peripheral tissues, including arterial walls, and transport it back to the liver. This process helps prevent cholesterol buildup in arteries, reducing the risk of heart disease, which is why HDL is considered 'good cholesterol'.

How does the script compare LDL particles to a garbage truck?

The script compares LDL particles to a garbage truck because, like a truck that needs to dump its load in the correct place, LDL should deliver cholesterol to organs that require it. However, if LDL deposits cholesterol in artery walls, it can cause blockages and inflammation, similar to a truck dumping garbage on the highway.

What are the major apolipoproteins present in the lipoprotein particles mentioned in the script?

The major apolipoproteins include apolipoprotein B-48 in chylomicrons, apolipoprotein B-100 in VLDL, and a variety of apolipoproteins in HDL, which is rich in protein content.

What is the biological significance of the different lipoprotein compositions and sources?

The different compositions and sources of lipoproteins reflect their distinct functions in lipid transport and metabolism. For example, chylomicrons transport dietary lipids from the intestine, while VLDL and LDL are involved in cholesterol transport from the liver, and HDL is involved in reverse cholesterol transport from peripheral tissues to the liver.

Outlines

00:00

🧬 Lipids and Proteins: The Basics of Lipoproteins

This paragraph introduces the concept of lipoproteins, which are particles composed of lipids and proteins. It explains that lipoproteins contain lipids such as cholesterol, triglycerides, and phospholipids, along with proteins like apolipoproteins. The paragraph also outlines the different types of lipoproteins found in the human body, including chylomicrons, VLDL (Very Low Density Lipoprotein), IDL (Intermediate Density Lipoprotein), LDL (Low Density Lipoprotein), and HDL (High Density Lipoprotein). Each type of lipoprotein has a distinct function and importance, with variations in protein content and lipid composition. For example, HDL has a high protein content compared to VLDL. The paragraph sets the stage for a deeper dive into the roles and metabolism of these particles.

05:00

🚀 Chylomicrons and VLDL: Synthesis and Metabolism

The second paragraph delves into the synthesis and metabolism of chylomicrons and VLDL. Chylomicrons are produced in the intestinal epithelial cells and are primarily composed of triglycerides derived from dietary fats. They are responsible for transporting dietary lipids to adipose tissue, where lipoprotein lipase breaks down triglycerides into free fatty acids for storage. The resulting chylomicron remnants are then taken up by the liver. The paragraph also discusses the synthesis of VLDL in the liver, which involves the conversion of glucose to fatty acids and cholesterol. VLDL particles are composed of triglycerides, cholesterol, and apolipoprotein B-100, and they play a role in delivering lipids to peripheral tissues. The interaction between VLDL and HDL is highlighted, with HDL donating apolipoproteins to VLDL, which in turn picks up triglycerides from adipose tissue.

10:01

🔄 LDL: The Transporter of Cholesterol

This paragraph focuses on LDL, which is rich in cholesterol and has a low triglyceride content. It explains the role of LDL in transporting cholesterol from the liver to peripheral tissues, such as the adrenal glands and testes, where it is used for the production of steroid hormones and testosterone. However, the paragraph also points out the potential harm of LDL, as it can deposit excess cholesterol in artery walls, leading to atherosclerosis and increasing the risk of heart disease. The clearance of LDL from the bloodstream is discussed, with LDL particles being recognized by hepatic receptors for apolipoprotein B-100, leading to receptor-mediated endocytosis and cholesterol recycling in the liver.

15:02

🛡️ HDL: The 'Good' Cholesterol and Its Protective Role

The final paragraph discusses HDL, known as the 'good' cholesterol, which is rich in apolipoproteins and plays a crucial role in reverse cholesterol transport. HDL interacts with VLDL and LDL, exchanging triglycerides for apolipoproteins and picking up excess cholesterol from peripheral tissues, including arterial walls, to prevent cholesterol-mediated damage. The paragraph emphasizes the protective function of HDL in contrast to LDL, which is considered 'bad' cholesterol due to its potential to cause arterial blockages and inflammation. The summary concludes with a brief overview of the main apolipoproteins associated with different lipoprotein particles and their sources, setting the stage for future videos that will explore these topics in greater detail.

Keywords

💡Lipoprotein

Lipoproteins are complex particles that consist of both lipids and proteins, playing a crucial role in transporting lipids such as cholesterol and triglycerides in the bloodstream. In the video, lipoproteins are the central theme, with the script discussing various types and their functions in metabolism and transport.

💡Chylomicron

Chylomicrons are a type of lipoprotein that is primarily responsible for the transport of dietary lipids from the intestine to other parts of the body. They are enriched with triglycerides and are the largest lipoproteins. The script mentions chylomicrons as the first type of lipoprotein discussed, highlighting their role in fat absorption from the diet.

💡VLDL (Very Low Density Lipoprotein)

VLDL stands for Very Low Density Lipoprotein and is a type of lipoprotein synthesized by the liver. It is involved in transporting endogenous triglycerides. The script explains VLDL's composition, which includes apolipoprotein B-100, and its role in lipid metabolism.

💡IDL (Intermediate Density Lipoprotein)

IDL, or Intermediate Density Lipoprotein, is a transient lipoprotein that is formed during the metabolic process from VLDL. It has moderate levels of triglycerides and cholesterol and is an intermediate step in the conversion of VLDL to LDL. The script describes the transformation of VLDL into IDL through the action of lipoprotein lipase.

💡LDL (Low Density Lipoprotein)

LDL, known as Low Density Lipoprotein, is a type of lipoprotein that carries cholesterol to body tissues. It is often referred to as 'bad cholesterol' because high levels can lead to plaque buildup in arteries. The script discusses LDL's high cholesterol content and its potential harmful effects if it accumulates in artery walls.

💡HDL (High Density Lipoprotein)

HDL, or High Density Lipoprotein, is considered 'good cholesterol' because it helps remove cholesterol from the bloodstream and transport it back to the liver for excretion or reuse. The script emphasizes HDL's high protein content and its role in reverse cholesterol transport.

💡Apolipoprotein

Apolipoproteins are proteins that bind to lipids to form lipoproteins. They play a crucial role in lipid transport and metabolism. The script mentions various apolipoproteins, such as A, B-48, B-100, C, and E, and their specific association with different types of lipoproteins.

💡Triglycerides

Triglycerides are a type of lipid found in the blood and are a primary source of energy for the body. The script discusses triglycerides in the context of chylomicrons and VLDL, highlighting their high content in these lipoproteins and their role in energy storage and transport.

💡Cholesterol

Cholesterol is a waxy substance found in the blood and is essential for the body's functions, such as hormone production and cell membrane integrity. However, high levels of cholesterol in the blood, particularly LDL cholesterol, can contribute to heart disease. The script explains the varying concentrations of cholesterol in different lipoproteins and its transport by LDL.

💡Lipoprotein Lipase

Lipoprotein lipase is an enzyme that plays a key role in the breakdown of triglycerides in chylomicrons and VLDL. It is activated by apolipoprotein C-II and is found in adipose tissue and muscle. The script describes how lipoprotein lipase helps in the metabolism of triglycerides by converting them into free fatty acids.

💡Receptor-Mediated Endocytosis

Receptor-mediated endocytosis is a cellular process where specific molecules are taken into the cell via receptors on the cell surface. In the context of the script, it explains how the liver removes LDL from the bloodstream by recognizing apolipoprotein B-100 on the LDL particle's surface and internalizing it.

Highlights

Lipoproteins are a combination of lipids and proteins, including cholesterol, triglycerides, and apolipoproteins.

Chylomicrons, VLDL, IDL, LDL, and HDL are the different types of lipoproteins with distinct functions and compositions.

Chylomicrons are rich in triglycerides and are secreted from the intestinal epithelial cells.

VLDL is secreted by the liver and contains apolipoprotein B100.

HDL is rich in proteins, with over 40% protein content, and is involved in reverse cholesterol transport.

Lipoprotein lipase, activated by apolipoprotein C2, breaks down triglycerides into free fatty acids in adipose tissue.

IDL is a transient form that interacts with HDL and LDL, further reducing its triglyceride content and increasing its cholesterol content.

LDL, known as bad cholesterol, transports cholesterol from the liver to peripheral tissues and can deposit cholesterol in artery walls, leading to coronary artery disease.

HDL, known as good cholesterol, picks up excess cholesterol from arteries and returns it to the liver, protecting against cardiovascular diseases.

Chylomicrons deposit triglycerides in adipose tissue and are then converted to chylomicron remnants, which are taken up by the liver.

VLDL particles acquire apolipoproteins C2 and E from HDL in the bloodstream.

VLDL deposits triglycerides in adipose tissue and converts to IDL, which then becomes LDL.

The major function of LDL is to transport cholesterol to tissues, including the adrenal gland and testes, for hormone synthesis.

LDL receptors in the liver recognize apolipoprotein B100 and mediate endocytosis of LDL particles for recycling.

HDL acts as a reservoir for apolipoproteins and helps in cholesterol esterification, aiding in cholesterol homeostasis.

Transcripts

hi everyone in this video we'll be

talking about right to protein

metabolism and the transport of

lipoprotein so what comes in our mind

when we hear the term lipoprotein so

it's simply lipid and protein right a

combination of both so inside the

lipoprotein particles there would be

repeats such as cholesterol

triglycerides phospholipids etc also

there would be a protein part such as

Apple lipoproteins a combination of all

of these is the lipoprotein now let me

introduce you to the lipoproteins there

are several types of lipoproteins which

are found in our body and they have

their distinct function and importance

so first lipoprotein that we are going

to talk about is chylomicron then we

will talk about VLDL ideal LDL and HDL

VLDL stands for very low density

lipoprotein whereas IDL stands for

intermediate density lipoprotein LDL is

low density lipoprotein while HDL is

high density lipoprotein when we say

some density of the lipoprotein we means

how much is the protein content or how

much protein is there for example in HDL

the protein content is pretty much it is

way more than the VLDL or very

low-density lipoprotein in order to

understand that we need to understand

what is the composition of these

particles so let's talk about the major

Apple lipoproteins present in these

particles first and then we talked about

the overall composition so chylomicron

has Apple iPod protein a Apple B 48 C

and E whereas VLDL has apolipoprotein B

100 so this is the difference between

VLDL and the kind of micron

it also has apolipoprotein see and

apolipoprotein e now after that in ideal

and LDL we both have a Appleby 100 and

in HDL we have majority of the

lipoproteins but if you go over the

overall constant composition of these

particle we would see that 90% of the

chylomicron is triglyceride actually the

triglyceride composition is very high in

case of VLDL and chylomicron whereas for

LDL the concentration of cholesterol is

very high almost 50% of it

so cholesterol has the highest density

of cholesterol whereas real deal and

chylomicron has the highest proportion

of triglycerides in contrast HDL has

higher proportion of apolipoproteins

almost 40% of it so once we have a

overview of the composition of this

particle let's see how these particles

are synthesized one of their functions

how are they metabolized and what is the

turnover rate so let's begin let's say

we eat a food which is enriched in fats

such as a cheesy burger and it would be

metabolized inside our GI tract right so

in the intestine the fact would be

absorbed in form of my sillies right now

in the intestinal epithelial cell the

substance which would be secreted from

the intestinal epithelial cell is the

chylomicron so intestinal epithelial

cell secretes chylomicron which is

enriched in triglycerides other than

triglyceride it has cholesterol Apple B

48 Apple II and Apple lipoprotein C 2

all of these are the components of

chylomicron right so chylomicrons are

exclusively assembled in the intestinal

mucosal sale and the most important

thing

them is they do have triglyceride but

these triglycerides are coming from our

diet all the triglyceride cholesterol

that it has it is coming from our diet

now triglyceride account for 90% of the

volume of this chylomicrons so these are

the two very important points about

chylomicron so this is the overall

composition of the chylomicron as we

have discussed now we wanted to

understand what is the function of

chylomicron so chylomicron can circulate

inside the bloodstream and eventually it

would encounter in the adipose tissue

now it's job is to deposit the

triglyceride

I mean deposit the fat t acids in the

triglyceride when it encounters adipose

tissue so on the adipose tissue there

would be specific enzymes known as

lipoprotein lipase now one part of the

chylomicron which is apolipoprotein c2

would activate the lipoprotein lipase

now lipoprotein lipase is an

extracellular enzyme that is anchored to

a heparin sulfate on the capillary walls

of many cell types and tissues but

majorly it is found in adipose tissue

and it is very important in terms of

breaking down of triglycerides so the

lipoprotein lipase is activated by a

palapa protein C 2 would be eventually

breaking down that fry as I whistle into

free fatty acids and these free fatty

acids would be stored inside the adipose

tissues so the major function of

lipoprotein lipase is to break down fat

and try as a glycerol and now the fact

is freed right so we can understand the

concentration of triacylglycerol is

reduced in these particle now it is

known as chylomicron remnant okay and it

would be up taken by the liver so now we

talk about another type of lipoprotein

particle which is known as VLDL or very

low density

which is exclusively secreted by the

liver not by the intestine so let's try

to understand how we LDL is synthesized

and secreted so we LDL is generated de

novo inside the liver right in the liver

hepatocytes so let's just zoom in to our

HEPA 2 side and try to understand

so liver hepatocytes input of blue COEs

from the bloodstream

now once glucose enters the liver

hepatocytes it would undergo glycolysis

and it would generate pyruvate

eventually that pyruvate would be

converted to acetyl co a and acetyl co

it would eventually give rise to a TCA

cycle and in to generate ATP in the

electron transport chain

now this acetyl co a can also be

utilized inside the smooth endoplasmic

reticulum reticulum to make cholesterol

so cholesterol biogenesis can takes

place in the smooth endoplasmic

reticulum now other than that the

dihydroxyacetone phosphate which is a

by-product of the glycolysis pathway can

be eventually used to make glycerol and

there would be free fatty acids present

in the cytosol itself so free fatty acid

visceral would make triacylglycerol

whereas cholesterol and phospholipid

would also be packaged inside the Golgi

bodies and ultimately it would generate

a lipoprotein particle right and the

protein part comes from these

apolipoprotein components and from liver

the Applebee 100 is the major eco

lipoprotein on VLDL and it is

synthesized by a specific gene present

in the nucleus okay so the

apolipoprotein be 100 containing v LDL

particles would be now released into the

bloodstream

now VLDL encounters HDL and from HDL

VLDL obtains other apple ipod protein

such as apple ipod protein C 2 and

apolipoprotein e so it is very important

that VLDL interacts with the

circulating HDL now as will really pass

through the circulation it also

encounters the fatty tissues or the

adipose tissues and on the adipose

tissues there would be lipoprotein

lipase so just like we have seen for the

chylomicron the lipoprotein lipase would

break down triglyceride and take it

right so once we LDL is depositing quite

a lot of free fatty acid in that opposed

tissue it would be now

deficient in terms of triglyceride it

would have less amount of triglyceride

so that intermediate compound which has

less amount of triglyceride moderate

amount of cholesterol a little bit

amount of proteins as well is known as

intermediate density lipoprotein notice

that they have reduced in size as well

now this ideal would actually interact

ideal is a very transient species and it

would interact with the HDL or high

density lipoprotein HDL would up take a

lot of triglyceride further from the

ideal and in contrast it would give some

amount of cholesterol and ester fide

cholesterol to the ideal as a result

this transient molecule of ideal would

have high level of cholesterol and it

further lose the triglyceride so it

would have no triglyceride very high

level of cholesterol and it would be now

known as LDL so LDL has very high level

of cholesterol and very low triglyceride

now LDL has several surface components

obviously it would have apolipoprotein C

and E it would have a piper between be

100 but eventually these C and E would

be taken by the HDL or it would be

utilized to activate LPL as a result

what would happen it would be left with

a PO be 100 now how LDL is metabolized

and that's the important question okay

so

LDLs major function is to transport

cholesterol from liver to the peripheral

tissue or otherwise it can return the

cholesterol into the liver so obviously

let's say the LDL particle which was

actually formed by the liver in format

of real deal would be ventually carrying

the cholesterol to the testes or to the

adrenal gland now generated from the

liver the LDL particle will be useful

for the adrenal cortex because the

cholesterol that would be deposited by

the real it would generate several

steroid hormones of adrenal cortex

similarly in case of testes the

cholesterol would be utilized to

generate testosterone so in real

transport cholesterol and it is

absolutely necessary for the body but

there is also a harmful side of LDL LDL

can deposit too much cholesterol in the

artery walls and that is detrimental it

would narrow the space of the arteries

and increase the risk of coronary artery

disease or many other heart disease now

this situation is not only detrimental

and it only block the blood flow but it

would also create a huge amount of

inflammation because these macrophages

or the dendritic cell would secrete

inflammatory cytokine in that region

overall it can create several as the

inflammatory symptoms now I would like

to imagine this phenomena just like a

garbage truck

so LDL particles are like garbage truck

they need to dump their garbage in the

dump yard and the garbage would be

recycled so it will need to dump their

cholesterol in the organ that require

cholesterol and it would be utilized so

no problem with that but the problem

comes when the garbage truck is dumping

their loads beside the highway one

possibility is the highway would be

blocked and there would be problem with

transport similarly for LDL when it

starts to dump the cholesterol on artery

walls it could be detrimental for the

body

it can create inflammation it can create

obstruction in the blood flow and

increase the risk of heart disease so

that was the overview of cholesterol as

a lipoprotein particle so we have a lot

of similarity of cholesterol transport

and cholesterol spatter physiology with

the dump truck now apart from that

cholesterol would be eventually taken by

the liver so in the liver hepatocytes

there are specific receptors against

apple b100 the in real receptors which

would recognize that would be 100

because coalesced the LDL particle has

Apple be 100 and ultimately it would

undergo receptor mediated endocytosis

and it would be up taken by the liver

hepatocytes and it would be recycled as

per demand so definitely the most

important components here is the Apple B

100 and the receptor mediated

endocytosis of LDL particle which

recognized a per beam 100 now we try to

understand about HDL now HDL is the

smallest apple lipoprotein in terms of

size but they have highest density of

apolipoproteins

they have quite a lot of proteins more

than 40% of HDL is protein so they have

room to take triglyceride and

cholesterol so HDL interact with real

deal and LDL and what they do is

exchange triglyceride in cost of apple

lipoproteins so it gives proteins to

VLDL and LDL whereas picks up

triglyceride from these triglycerides

and cholesterol esters from these

species now the HDL is a resolver for

apolipoprotein HDL can uptake under

stiff esterified cholesterol as well as

esterified now HDL

helps in the esterification process of

cholesterol and majorly HDL takes part

in the diversed cholesterol transport so

it's a garbage pickup truck so let's say

even if you have garbage on the side of

the highway and there's a pickup truck

which is picking up the garbage then

it's fine right

so HDL try to a pick excess amount of

cholesterol which is dumped on the

arteries and try to save our body from

risk of cholesterol mediated damages in

our artery

so that is why HDL is also known as good

cholesterol while LDL is known as bad

cholesterol so let's just take a quick

overview that what we learned in this

overall video in this video we have a

clear idea about what are the major

apolipoproteins presenting these

lipoprotein particles right so we have

seen chylomicron contains apple b48 as a

signature apple lipoprotein whereas VLDL

has apple b100 now HDL is very rich with

proteins the composition of all of these

lipoprotein particle are different now

chylomicron and VLDL are very enriched

in try SIV so all whereas LDL is

enriched in cholesterol and HDL is found

to be enriched with proteins and we also

looked at the source from which these

particles are secreted we have seen

chylomicron is secreted from intestine

whereas these veal really ideal angular

particles are generally coming from the

liver

whereas HDL can be secreted from both

liver and the interesting so that goes

over all bird's eye view on this

particular topic but in subsequent

videos we'll be talking about all of

these species in lot more details and

try to understand their characteristics

pathophysiology and there are biological

significance so I hope you enjoyed this

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