The aim of this investigation is to explore the effect of different concentrations of bile salts on the time taken for the lipase enzyme to break down fat.
Bile is a brownish bitter alkaline fluid produced by the liver and made by the hepatocytes from water, bile salts, bile pigments cholesterol and phospholipids and stored in the gall bladder. Bile is directly connected with digestion. It is released sporadically into the small intestine (duodenum) which is part of the gut in order to help digestion. Bile contains chemicals that break down/emulsify fats by dispersing fat globules into small droplets, therefore increasing the surface area, in turn speeding up the reaction. When fats get to the small intestine they activate the discharge of secretin and cholecystokinin-pancreozymin (CCK-PZ). Secretin encourages bile production, and CCK-PZ promotes the release of bile into the small intestine.
The bile salts help in the breakdown and absorption of fats, while bile pigments break down products of old red blood cells, which are passed into the gut to be eradicated with the faeces.
Lipase is the enzyme responsible for breaking down fats into fatty acids and glycerol. It is produced by the pancreas and requires a slightly alkaline environment. Some of the lipase is secreted in the saliva. The products of fat digestion are absorbed by the intestinal wall.
This water-soluble enzyme that catalyses the hydrolysis of ester bonds in water-insoluble, lipid substrates, is the main enzyme responsible for breaking down the fats in the human digestive system.
There's more than just the one kind of lipase in the human body: Lysosomal lipase, hepatic lipase, endothelial lipase, pancreatic lipase, gastric lipase.
People with pancreatic shortage and cystic fibrosis often need supplemental lipase and other enzymes.
Phenolphthalein is a pH and is often used in titrations; it turns from colourless in acidic solutions to pink in basic solutions.
In strongly basic solutions, phenolphthalein's pink color undergoes a rather slow fading reaction and becomes colourless again.
Below pH 8.2 = Colourless
Above pH 10.0 = Pink
The diagram below shows in a few steps how the enzyme works
From this diagram it is apparent that the catalase active site is complementary to that of the substrate, hydrogen peroxide. There are two theories for the binding of the substrate to the enzyme. These are: 1.
Lock & Key = This is where the active site of an enzyme is specific for only one type of enzyme, so only one type of substrate can bind with it. This is due to the shape of the enzymes active site in relation to the substrate. E.g. Reaction where amylase breaks down starch to maltose. 2.
Induced Fit = this is where the substrate makes the enzyme mould round the substrate. The only difference here is that the enzyme changes, however maintains enzyme specific ideas,
Unsystematic movement of the enzyme and substrate brings the substrate into the enzyme's active site. This position is only held temporarily whereby the R groups of the amino acids react with the substrate.
This contact with the active site forms product(s), which leave the enzyme molecule unchanged & ready to bind with other substrates.
Enzymes are calalysts & therefore increase the rate at which chemical reactions occur. If enzymes did not exist in living cells the reactions would happen extremely slowly.
The substrate will not be converted, in many reactions, to a product unless it is momentarily given some extra energy, which is called activation energy.
Chemical reaction without enzyme
Chemical reaction with enzyme
Here it is clear that enzymes reduce the amount of activation energy that is required. This speeds up the rate of reaction.
Enzymes in the human alimentary canal and what they digest:
Bibliography: Mammalian Physiology & Behaviour – OCR
A2-level Biology Revision Guide for OCR – CGP
© CLEAPS 1995
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