Mobilization of Triglycerides in Adipose Cells

inside our body we have these specialized cells known as adipose cells that function to basically store fatty acids in their triglyceride form so if we look within a cytoplasm of these adipose cells will find these large structures known as fat globules and these fat globules consist entirely of individual triglyceride molecules now we know the cells of our body can actually use these triglyceride molecules to help generate ATP molecules but how exactly does this process actually take place so as we'll see in just a moment the utilization of these triglycerides to actually help us generate these high-energy ATP molecules involves three different steps three different stages so in stage one these triglycerides are actually broken down and mobilized into their fatty acid and glycerol form once that takes place that fatty acids are released into the bloodstream and the bloodstream carries these molecules the fatty acids to their target cell once the fatty acid makes its way into the cytoplasm of that target cell that's when stage B actually takes place and in stage B these fatty acids are activated they're made more reactive and then they're transported into the matrix of the mitochondria and that's when stage C begins in stage C those fatty acids are broken down in the matrix of the mitochondria into acetyl coenzyme a molecules and these acetyl coenzyme a molecules can be fed it's the citric acid cycle to help us generate the high energy ATP molecules now in this lecture what I'd like to focus on it's is stage a so the breakdown and the mobilization of these triglycerides into fatty acids and glycerol molecule molecules and this takes place within these adipose cells fat cells of our body so let's suppose that we just woke up and after waking up we basically want to go for a run or a swim so we want to carry out some type of sighs now overnight what happened was the cells of our body used up their supply of glucose and glycogen and so as soon as we go for that morning run or swim our cells will depend on triglycerides to actually form that the ATP molecules that are needed to carry out those particular cell processes and so the question is what actually initiates the breakdown and the mobilization of triglycerides within our fat cell in this circumstance well basically specific types of hormones so we have hormones such as glucagon and epinephrine that can initiate the breakdown of the mobilization of triglycerides so we have some type of primary messenger molecule so it can be glucagon or it can be epinephrine that binds on to a specific seven transmembrane protein receptor found on the membrane of adipose cells and once it actually binds it creates a conformational change in that 70m structure and that causes structural changes in the g protein and what that does is it releases the GDP and it basically accepts the gtp and once the GTP binds onto that g protein and activates the protein and the protein then travels and binds unto another membrane molecule known as adenylate cyclase and what this enzyme basically does is upon the binding it is activated upon the binding of the g protein it is activated and it begins the conversion of ATP molecules into cyclic GMP molecules and the cyclic ANP is a secondary messenger in this particular signal transduction pathway now the cyclic AAP molecules then move on to target protein so PKA molecules protein kinase a so cyclic AMP II bites onto the regulatory units of the PKA that causes the dissociation of the catalytic units from the PKA and that activates the PK and once the pKa is actually actively a protein kinase a goes on to phosphorylate and activate two important types of enzymes involved in the breakdown and the mobilization of triglycerides so what are these important enzymes well one of them is known as Paralympian a and the other set of enzymes are known as hormone sensitive lipase so these two enzymes work together to basically help break down these triglycerides into fatty acids and glycerol molecules more specifically the para Lipan a basically binds onto the fat globules found in the cytoplasm of adipose cells and they stimulate the remodeling and the restructuring of these fat globules what that does is it exposes the ester bonds of the triglycerides and now the hormone sensitive lipase is such as triglyceride lipase essentially bind onto those exposed ester bonds and begin cleaving breaking hydrolyzing those triglyceride ester bonds and so ultimately we transform the triglycerides into the individual free-floating fatty acids and the glycerol molecules and once that takes place these two molecules in there mobilize form are now released into the bloodstream now once inside the bloodstream what happens next well glycerol molecules contain one to three hydroxyl groups and that makes them polar molecules and because our blood plasma consists predominantly of water that means glycerol will be soluble in the blood plasma and so it will not actually require any type of protein carrier to transport within the blood plasma now glycerol molecules ultimately end up in liver cells and we'll discuss exactly what happens to the glycerol molecules in just a moment but first let's actually look at these fatty acids now fatty acids contain this relatively long hydrocarbon chain to our group and that makes fatty acids insoluble in water and so they will not be able to actually dissolve in our blood plasma and unlike glyceryl molecules fatty acids will require a protein transporter molecule and this molecule is known as serum albumin so serum albumin actually binds fatty acids in the blood plasma and it carries those fatty acids to the target cell and in the example that I gave before the target cell that the fatty adds are carried to our the skeletal muscle cells that help us carry out the different types of voluntary motion voluntary motions now what happens to the glycerol well the glycerol as I said earlier moves into liver cells and once inside the cytoplasm of liver cells an enzyme known as glycerol kinase traps that glycerol inside that liver cell and it traps it by giving it a negative charge so it actually takes off a pass for group from an ATP places it onto the oxygen of glycerol forms an ADP as well as the L isomer of glycerol 3-phosphate and this traps the glycerol inside that particular liver cell now what happens next is that glycerol 3-phosphate is transformed into dihydroxyacetone phosphate by the enzyme glycerol phosphate dehydrogenase and it also actually reduces the nad plus and generates NADH so this is essentially an oxidation reaction where the glycerol 3-phosphate is oxidized into the dihydroxyacetone phosphate and once we form this it is then transformed into the g isomer of glyceraldehyde 3-phosphate and recall that glyceraldehyde 3-phosphate is an intermediate of both the glycolytic pathway glycolysis as well as gluconeogenesis now the fate of this glyceraldehyde 3-phosphate basically depends on the conditions of the body and the liver cell so essentially if we need to generate ATP molecules within a liver cell then the glyceraldehyde 3-phosphate can basically undergo glycolysis we can form pyruvate and that can help us generate ATP molecules on the other hand if the liver cells have to maintain let's say increase the blood glucose levels in our body then the glyceraldehyde 3-phosphate can undergo gluconeogenesis and form the glucose molecule and the glucose can be released into the blood plasma of our body to help regulate and maintain the proper glucose levels of the body so we see that the glitter we see that the glycerol that is formed from the breakdown of the triglycerides ultimately ends up in the liver cell and it can be used by the liver cell to basically hate I help maintain the correct blood glucose levels and also help generate ATP molecules needed by that liver cell now what happens to the fatty acids well this is what I'd like to focus on in the next lecture in the next lecture we're going to discuss how these fatty acids are activated within the target cell and then transport it into the matrix of the mitochondria of that target cell

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Keywords: mobilization of triglycerides, mobilization of triglycerides in fat cells, triglycerides, breakdown of triglycerices into fatty acids, breakdown of triglycerides, triglyceride degradation, glucagon and fatty acids, triacylglycerols, triglycerides in adipose cells, perilipin A, hormone sensitive lipases, triglyceride lipase, biochemistry, fatty acid metabolism, triglyceride metabolism

Id: yFqyVA_I2N0

Length: 9min 57sec (597 seconds)

Published: Wed Jul 29 2015