The Comparison of Lipase Digestion with and without Bile Salts
Aim
The aim of this investigation is to see how the presence of bile salts, effects the rate at which lipase digestion takes place.
Introduction
The process that is taking place in this investigation is emulsification. Emulsification is the dispersal of tiny droplets of a water insoluble, substances, such as fats, into water. This occurs in lipid digestion. Lipid digestion begins in the stomach, where the enzyme lipase breaks triglycerides into fatty acids and glycerol. This process doesn't get very far in the stomach so the majority of fat digestion takes place in the duodenum and ileum, where pancreatic juice containing more lipases is added from the pancreas. Lipase, like all enzymes are globular proteins with their own specific catalytic action. Enzyme molecules have a complicated three-dimensional shape due to the particular way the amino acid chain that makes up the protein is folded. This tertiary protein structure gives the enzyme its catalytic ability. In each enzyme there is a specific indentation, called the active site, into which only certain specific substrate molecules will fit. The shape of the active site, position of the various chemical groups ensure that only those substrates with a complementary structure will combine with the enzymes and react. In an enzymatic reaction, the substrate binds to the active site to form an enzyme-substrate complex. Usually, the substrate is held in the active site by weak bonds, such as hydrogen or ionic. Catalytic amino acids then catalyse the conversion of the substrate to a product. The product is then released from the active site as it doesn't have the complementary structure and therefore the enzyme is free to take another substrate to replace it.
There are also several variables that could affect the rate of an enzymatic reaction, for example, temperature, pH, concentration of substrate etc and some enzymes, like lipase, work better if other substances are also present e.g. lipases are more effective if emulsifying agents e.g. bile salts, are present because they break up the substrate into smaller droplets.
Bile, a viscous, greenish yellow fluid is secreted by the hepatocytes in the liver and is stored and concentrated in the gall bladder. After storage, it is carried along the bile duct into the duodenum. The stimulus for the release of bile into the duodenum is the presence of the hormone cholecystokinin-pancreozymin. Bile is composed of 98% water, 0.2% bile pigments, 0.7% inorganic salts, 0.6% cholesterol and 0.8% bile salts. Not all of these substances are involved in digestion. Those that are, are the bile salts. Bile salts are derivatives of the steroid cholesterol, which is synthesised in the hepatocytes. The most common bile salts are sodium glycocholate and sodium taurocholate. They are secreted with cholesterol and phospholipids as large particles called 'micelles.' The cholesterol and the phospholipids hold the polar bile salt molecules together so that all the hydrophobic ends of the molecules are orientated the same way. The hydrophobic ends attach to lipid droplets whilst the other ends are attached to water. This emulsifies the fats by decreasing the surface tension of the droplets and enabling the lipids to separate causing them to break up into tiny droplets. This therefore increases the surface area of fat, thereby facilitating the digestion action of the enzyme lipase.
Aim
The aim of this investigation is to see how the presence of bile salts, effects the rate at which lipase digestion takes place.
Introduction
The process that is taking place in this investigation is emulsification. Emulsification is the dispersal of tiny droplets of a water insoluble, substances, such as fats, into water. This occurs in lipid digestion. Lipid digestion begins in the stomach, where the enzyme lipase breaks triglycerides into fatty acids and glycerol. This process doesn't get very far in the stomach so the majority of fat digestion takes place in the duodenum and ileum, where pancreatic juice containing more lipases is added from the pancreas. Lipase, like all enzymes are globular proteins with their own specific catalytic action. Enzyme molecules have a complicated three-dimensional shape due to the particular way the amino acid chain that makes up the protein is folded. This tertiary protein structure gives the enzyme its catalytic ability. In each enzyme there is a specific indentation, called the active site, into which only certain specific substrate molecules will fit. The shape of the active site, position of the various chemical groups ensure that only those substrates with a complementary structure will combine with the enzymes and react. In an enzymatic reaction, the substrate binds to the active site to form an enzyme-substrate complex. Usually, the substrate is held in the active site by weak bonds, such as hydrogen or ionic. Catalytic amino acids then catalyse the conversion of the substrate to a product. The product is then released from the active site as it doesn't have the complementary structure and therefore the enzyme is free to take another substrate to replace it.
There are also several variables that could affect the rate of an enzymatic reaction, for example, temperature, pH, concentration of substrate etc and some enzymes, like lipase, work better if other substances are also present e.g. lipases are more effective if emulsifying agents e.g. bile salts, are present because they break up the substrate into smaller droplets.
Bile, a viscous, greenish yellow fluid is secreted by the hepatocytes in the liver and is stored and concentrated in the gall bladder. After storage, it is carried along the bile duct into the duodenum. The stimulus for the release of bile into the duodenum is the presence of the hormone cholecystokinin-pancreozymin. Bile is composed of 98% water, 0.2% bile pigments, 0.7% inorganic salts, 0.6% cholesterol and 0.8% bile salts. Not all of these substances are involved in digestion. Those that are, are the bile salts. Bile salts are derivatives of the steroid cholesterol, which is synthesised in the hepatocytes. The most common bile salts are sodium glycocholate and sodium taurocholate. They are secreted with cholesterol and phospholipids as large particles called 'micelles.' The cholesterol and the phospholipids hold the polar bile salt molecules together so that all the hydrophobic ends of the molecules are orientated the same way. The hydrophobic ends attach to lipid droplets whilst the other ends are attached to water. This emulsifies the fats by decreasing the surface tension of the droplets and enabling the lipids to separate causing them to break up into tiny droplets. This therefore increases the surface area of fat, thereby facilitating the digestion action of the enzyme lipase.
