Introduction to lipoproteins

the next topic that we're going to talk about will be the metabolism of lipoproteins but what exactly are lipoproteins and what is the function of lipoproteins so remember when we ingest or synthesize molecules such as triglycerides and cholesterol these molecules are very hydrophobic and that means they can't simply dissolve in the blood and so to keep them dissolved in an aqueous environment and transport them throughout the bloodstream we have to generate these lipoproteins these transport molecules that keep triglycerides and cholesterol dissolved and move them to and from tissues so lipoproteins are spherical structures made up of lipids and proteins that help keep fats dissolved in the blood and transport them to and from tissues and on the board I've listed the major types of life proteins that you have to be familiar with we have the chylomicrons and the kyla Mike and the chylomicron remnants these are part of the exogenous transport pathway then we have the very low-density lipoproteins vldls we have something called intermediate density lipoproteins IDL's and we have low-density lipoproteins LDL and these are collectively part of the endogenous transport pathway and then we have high density lipoproteins Shh CLS and these are part of the reverse cholesterol pathway now chylomicrons and their remnants very low density lipoproteins intermediate density lipoproteins and low density lipoproteins have pro atherogenic properties and what that means is if these are present in the bloodstream of the person and high quantities that increases the risk of developing atherosclerosis in contrast high density lipoproteins are anti atherogenic what that means is if these are present and high quantities they decrease the risk of developing atherosclerosis and that's exactly why LDLs are called the bad cholesterol and HDL is called the good cholesterol and we'll come back to this later on let's talk about the composition the size and the density of plasma lipoproteins so here we have a spherical structure remember the entire point of a lipoprotein is to create a structure in which we can dissolve those hydrophobic molecules so in the core at the center we have the triglycerides and we have cholesterol esters these are very hydrophobic cholesterol molecules and so these are present in the hydrophobic core that is shown in orange and around the core we create a shell and the shell consists of these amphipathic molecules that contain hydrophilic regions and hydrophobic regions the hydrophobic regions of these molecules interact with the hydrophobic core while the hydrophilic regions of the molecules interact with the nearby aqueous environment within the blood and so the shell consists the phospholipids and consists of proteins and also free cholesterol so lipoproteins are made up of hydrophobic core that consists of triglycerides and ester fide cholesterol this hydrophobic core is surrounded by the hydrophilic layer that consists of phospholipids proteins called Apryl lipoproteins we'll come back to these at the end and free cholesterol now where do we get the triglycerides and the cholesterol ester so they come either from our diet or they can actually come from then novus synthesis within our cell so our cells can synthesize these molecules from scratch inside the cell now generally speaking lipoproteins are divided based on their density but what determines the density of that lipoprotein so in general the greater the protein content and the lower the fat content the triglyceride content the more dense that molecule actually is and so let's take a look at the following four molecules so as we go from this side to this side notice that the size decreases but the density increases so let's begin with chylomicrons remember chylomicrons are part of the exon transport pathway so chylomicrons consists predominantly of triglycerides about 90% of the content is triglycerides and that's what makes them very very large they're 5% cholesterol which includes cholesterol esters and free cholesterol 3% phospholipids and only 2% protein and so notice the protein to triglyceride ratio is actually very very low and so that's why these chylomicrons are the least dense they're the largest and size but the least dense then we have the second least dense are the very low density lipoproteins these are made up of 60% triglycerides 20% cholesterol 15% phospholipids and only 5% protein then we have the low density lipoproteins these contain 8% triglycerides 50% cholesterol 22% phospholipids and 20% protein and in between these molecules we have the intermediate density lipoprotein IDL's we'll talk about them later on and finally the smallest in size but the most dense are the high density lipoproteins the good cholesterol that is part of the reverse cholesterol pathway so they're made up only 5% triglycerides but 40% proteins in addition they contain 30% phospholipids and 25% cholesterol so because here we have a ton of proteins but we don't have a lot of triglycerides that makes them the smallest but the most dense so chylomicrons are largest in size but the least dense while the high density cholesterol are the smallest in size but the most dense now let's finish off by briefly talking about what these Apryl lipoproteins are so April live proteins also known as April proteins are simply the proteins which help dissolve these triglycerides and cholesterol in the blood so they help make up the shell of this lipo pro and they actually have four major roles depending on the type of a polite protein we're talking about some a polite proteins are important in guiding the formation of that lipoprotein some provide structural support and give the structure integrity others act as ligand for receptors such as LDL receptors and some can actually activate or even inhibit certain types of enzymes now in general Apryl lipoproteins are divided into five major classes based on the structure and the function now don't worry too much about what the function of these aprile lipoproteins are and what they are we're going to talk about that in more detail later on but very briefly I just want to talk about the fact that we have these different types of april lipoproteins and they serve specific functions so for example we have a polite protein a so we have a1 and a2 a1 provides structural support for HDL and it activates the L cat enzyme a polite protein ates you also provide structural support for HDL but this one activates hepatic lipase a polite protein b48 provides structural support for chylomicrons which remember our part of the rivera which are part of the exogenous transport pathway and so they're generated in the intestines then we have a polite protein b100 this provides support for VLDL molecules LDL molecules uh ideal molecules and this also acts as a ligand for LDL receptors and so forth so again don't worry too much about these we're gonna talk about them in much more detail later on

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Keywords: lipoproteins, introduction to lipoproteins

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Length: 8min 27sec (507 seconds)

Published: Sun Jun 30 2019