Lipid metabolism

• How many grams of lipids does an average adult human eat per day?

  100-150 grams
• What are the main lipids found in the diet?

  Triacylglycerols
• What percentage of dietary lipids are triacylglycerols?

  99%
• What are the roles of lipids in the diet?

  Lipids provide energy, essential fatty acids, fat-soluble vitamins, and make the diet palatable.
• Why are long-chain fatty acids considered ideal storage fuel reserves?

  They can support the body's energy needs for long periods of food deprivation.
• What are the major components of cell membranes?

  Phospholipids, glycolipids, and cholesterol
• How are insoluble lipids transported in the bloodstream?

  They are solubilized in association with proteins to form lipoproteins.
• What is the significance of plasma lipid levels?

  They are useful for assessing the health of individuals.
• What is lipogenesis?

  It is the synthesis of triacylglycerols from fatty acids and glycerol.
• Where does triacylglycerol synthesis mostly occur?

  In the liver and adipose tissue
• What must fatty acids and glycerol undergo before triacylglycerol synthesis?


  They must be activated.
• How is glycerol phosphate formed in the liver?

  From glycerol by glycerol kinase or from glucose through glycolysis.
• What is the role of glycerol kinase in glycerol metabolism?

  It activates glycerol to form glycerol phosphate in the liver.
• How is glycerol phosphate formed in muscle and adipose tissue?

  From glucose through glycolysis.
• What catalyzes the synthesis of triacylglycerol?

  The reaction between acyl CoA and glycerol phosphate.
• Where is acyl-CoA formed?

  In the cytosol
• What enzyme catalyzes fatty acid activation to acyl-CoA?

  Acyl-CoA synthetase
• What are the two mechanisms for synthesizing glycerol 3-phosphate?

  Activation of glycerol by glycerol kinase and conversion from glucose through glycolysis.
• What is the role of glycerol 3-phosphate acyltransferase?


  It catalyzes the transfer of an acyl group to produce lysophosphatidic acid.
• What is formed when another acyl group is added to lysophosphatidic acid?

  Phosphatidic acid
• What does phosphatase do to phosphatidic acid?

  It cleaves off the phosphate to produce diacylglycerol.
• How is diacylglycerol converted to triacylglycerol?

  With the help of 1,2 diacylglycerol acyl transferase.
• What factors regulate triacylglycerol synthesis?

  Availability of fatty acids and glycerol, and intake of dietary fatty acids and glucose.
• What are the functions of phospholipids?

  They are involved in membrane structure, blood clotting, and supply arachidonic acid for prostaglandin synthesis.
• Where does phospholipid synthesis occur?

  In the smooth endoplasmic reticulum.
• What distinguishes different phospholipids?

  The polar base is the major distinguishing factor.
• What are the substrates required for phospholipid synthesis?

  Choline or ethanolamine, and 1,2 diacylglycerol 3-phosphate (phosphatidic acid).
• What is the process for forming lecithin and cephalin?

  Choline and ethanolamine are phosphorylated and react with ATP, catalyzed by choline kinase.
• How is phosphatidylserine formed?

  From phosphatidyl ethanolamine directly.
• What is the structure of phosphatidic acid?

  Glycerol + saturated fatty acid at position 1, unsaturated fatty acid at position 2, and phosphoric acid at position 3.
• What is the function of phosphatidic acid?

  It has no function and is produced as an intermediate in the synthesis of triacylglycerols and phospholipids.
• What is lecithin and its function?

  Lecithin (phosphatidyl choline) is the most abundant phospholipid in cell membranes.
• What is cephalin and its function?

  Cephalin (phosphatidyl ethanolamine) is involved in the coagulation mechanism.
• What is phosphatidylserine and its structure?

  Phosphatidylserine is similar to lecithin but contains serine instead of choline.
• What is lipositol and its function?

  Lipositol (phosphatidylinositol) acts as a precursor of second messengers in hormonal action inside cells.
• What are glycolipids and their simplest form?


  Glycolipids are derivatives of ceramide, and the simplest form is cerebrosides containing ceramide bound to monosaccharides.
• What are the common types of glycosphingolipids?

  Galactocerebroside and glucocerebroside.
• What is the role of galactocerebroside in the body?

  It is a major component of membrane lipids in nervous tissue, particularly in the myelin sheath.
• What is glucocerebroside's role in the body?

  It is an intermediate in the synthesis and degradation of complex glycosphingolipids.
• How many grams of lipids does an average adult human eat per day?

  100-150 grams