Year 10 Enzymes and Digestion PDF

Topic 1 Enzymes and Digestion Year 10 Ms Rose Marie Azzopardi Ms R. M. Azzopardi 1 1.r. Enzymes Enzymes are made up of proteins, so in the same way as proteins behave, so do enzymes. These...

Topic 1 Enzymes and Digestion Year 10 Ms Rose Marie Azzopardi Ms R. M. Azzopardi 1 1.r. Enzymes Enzymes are made up of proteins, so in the same way as proteins behave, so do enzymes. These special proteins are very important as they speed up reactions. Enzymes are biological catalysts which speed up the rate of reactions without being used up or destroyed. 1.s. Chemical and biological nature of enzymes Proteins are made up of Carbon (C), Nitrogen (N), Oxygen (O) and Hydrogen (H). Proteins are made up of amino acids which are the monomers of the larger polymer (the complex structure). Ms R. M. Azzopardi 2 1.t. Factors affecting enzymes Being protein, enzymes function within a narrow range of temperature, and are specific and sensitive to pH. Enzymes Inactive become enzyme at denatured low at high temperatu Temperature: The higher the temperature (below 40⁰C), the faster the activity of enzymes becomes. At too low temperatures, the enzymes become inactive and work very slowly. The higher the temperature, the more Kinetic energy is found in molecules, so the faster they move, making them work faster. Different enzymes have different optimum temperatures at which they work best. Human enzymes work best at body temperature which is between 36- 38˚C. Enzymes also get denatured above 40⁰C (not the same for all enzymes) and become inactive at low temperatures. In fact, enzymes work differently according to temperature, pH, surface area and concentration. Ms R. M. Azzopardi 3 pH: The optimal pH is different for different enzymes. For example the optimal pH of pepsin (the enzyme found in the stomach), is 2 (very acidic); whilst the optimal pH of catalase is between 4-11 (found in every cell). Draw a graph of enzyme activity (y axis) vs pH (x axis) EXTRA INFORMATION Surface area and concentration: The larger the surface area and the larger the concentration of the enzyme, the faster the rate of reaction would be. Ms R. M. Azzopardi 4 1.u. Enzymes are substrate specific Anabolic reaction Catabolic reaction Build-up Break down The enzyme substrate complex is a temporary molecule formed when an enzyme comes into perfect contact with its substrate. Substrate = starting substance which the enzyme will act on Product = the finished substance after that the enzyme acted on the substrate Enzymes can either build up (anabolism) or else break down (catabolism) a substance. The substance getting in an enzyme before the chemical is called a substrate. The final substance exiting the enzyme is called a product. For a substrate to get into an enzyme, it has to “FIT” like a glove; known as the Induced fit Theory. This makes enzymes very substrate specific, at specific temperatures and pHs. Ms R. M. Azzopardi 5 Economic importance of enzymes: Enzymes are widely used in the industry: 1. Rennin is used for coagulation of milk to make cheese 2. Cellulase and amylase are used to remove waxes, oils and starch coatings on fabrics and improve the look of final product 3. Amylase and protease are used for baking 4. Proteases, lipases, oxidase, amylases, oxidases, and cellulases are used in detergents 2.g, h & i. Nutrition Animals as consumers Holozoic nutrition: This is a type of nutrition (feeding) typical of animals (e.g. Amoeba and mammals) where organic food is obtained from other living organisms. In holozoic nutrition, food organisms are killed; ingested into a gut; digested (dissolved) by enzymes secreted internally; soluble products are absorbed into the bloodstream and carried by the blood all around the body; and indigestible waste is egested (eliminated). Ms R. M. Azzopardi 6  Saprophytic nutrition: This is the way bacteria and decay fungi (e.g. Mucor and mushrooms) feed. They obtain organic food from dead matter. Dead organisms or excreta are digested by enzymes secreted externally on them; soluble products are absorbed. Holophytic nutrition: Typical to green plants. These are able to build up their own organic food. Carbon dioxide and water are combined in photosynthesis to make carbohydrates. Carbohydrates are modified and also often combined with salts to form other organic molecules e.g. protein. Ms R. M. Azzopardi 7 HOLOZOIC SAPROPHYTIC HETEROTROPHIC - organisms that feed on ready-made organic food PARASITIC HOLOPHYTIC AUTOTROPHIC – Organisms that need only inorganic sources from which they synthesise organic molecules, using energy trapped from sunlight to drive the reactions Holozoic nutrition in animals Ms R. M. Azzopardi 8 Draw the digestive system Ms R. M. Azzopardi 9 Ingestion: is the act of taking food into the alimentary canal (or gut) through the mouth. Incisors are important for cutting food and adding surface area to the food for faster enzyme action (salivary amylase). Canines are found in carnivores and omnivores. They are sharp and pointed, and are used to tear food apart. Pre-molars and molars are important to crush and chew food. Note: strictly speaking, the mouth is the aperture between the lips. The space inside, containing the tongue and teeth is called the buccal cavity. Beyond the buccal cavity, is the ‘throat’ or pharynx. For food to enter the oesophagus (gullet), it must pass over the windpipe. All the actions which occur during swallowing ensure that food doesn’t enter the windpipe and cause choking. a) The tongue presses upwards and back against the roof of the mouth, forcing a pellet of food, called a bolus, to the back of the mouth. Ms R. M. Azzopardi 10 b) The soft palate closes the nasal cavity at the back. c) The larynx cartilage round the top of the windpipe (glottis) lies under the back of the tongue. d) The glottis is also partly closed by the contraction of a ring of muscle. e) The epiglottis, a flap of cartilage helps to prevent the food from going down the windpipe instead of the gullet. Physical digestion: this is when the teeth are used to break down large food particles into smaller particles. Chemical digestion: this is when large molecules of food are broken down into smaller molecules. This type of digestion takes place in the presence of enzymes. Physical digestion prepares the food for chemical digestion by increasing the surface area of the food. The larger the surface area, the faster the chemical digestion occurs, as there is more space available for the enzymes to act upon. The beginning of the swallowing action is voluntary, but once the food reaches the back of the mouth, swallowing becomes an automatic or reflex action. The food is forced into and down the oesophagus (or gullet), by peristalsis, and then the food is admitted to the stomach. Peristalsis- The walls of the alimentary canal contain circular and longitudinal muscle fibres. The circular muscles, by contracting and relaxing alternatively, urge the food in a wave-like motion through the various regions of the alimentary canal. Ms R. M. Azzopardi 11 Digestion: Is the process by which insoluble food, consisting of large molecules, is broken into soluble compounds having smaller molecules. It is the process by which solid food is dissolved to make a solution. The small molecules can pass through the epithelium of the alimentary canal, through the walls of the blood vessels and into the blood. The chemicals which dissolve food are enzymes. Enzymes are chemical compounds, protein in nature, made in the cells of living organisms. Most of the enzymes are intracellular, that is they carry out their functions in the protoplasm of the cell in which they are made. Some enzymes, however, are secreted out of the cells in which they are made, to be used elsewhere. These are called extracellular enzymes. Bacteria and fungi secrete such extracellular enzymes into the medium in which they are growing. The higher organisms secrete enzymes into the alimentary tract to act on food taken into it. These digestive enzymes accelerate the rate at which insoluble compounds are broken down into soluble ones. Enzymes which act on starch are called amylases, those acting on proteins are proteinases, and lipases act on fat. All the solid starch in foods such as bread and potatoes is digested to glucose which is soluble in water. The solid proteins in meat, egg and beans are digested to soluble substances called amino acids. Fats are digested to two soluble products called glycerol and fatty acids. STARCH GLUCOSE PROTEINS AMINO ACIDS FATS FATTY ACIDS and GLYCEROL The chemical breakdown usually takes place in stages. For example, the starch molecule is made up of hundreds of carbon (C), hydrogen (H) and oxygen (O) atoms. The first stage of digestion breaks it down to a 12- carbon sugar Ms R. M. Azzopardi 12 molecule called maltose. The last stage of digestion breaks the maltose molecule into two 6-carbon sugar molecules called glucose. Protein molecules are digested first to polypeptides, then to dipeptides and finally into amino acids. Digestion in the mouth In the mouth, the food is chewed and mixed with saliva. Chewing reduces the food to suitable sizes for swallowing and increases the available surface for enzymes to act on. Saliva is a digestive juice secreted by three pairs of glands, the ducts of which lead into the mouth. It is a watery fluid, not particularly acid or alkaline, containing a little mucus, which helps to lubricate the food and makes the particles adhere to one another. An adult may secrete from 1 to 1.5 L of saliva per day. One enzyme, salivary amylase, is present in saliva. Salivary amylase acts on cooked starch and begins to break it down into maltose, a soluble sugar. The longer food is retained in mouth, the further this starch digestion proceeds and the more finely divided the food become as a result of chewing. In fact, even well-chewed food does not remain in the mouth long enough for much Ms R. M. Azzopardi 13 digestion of starch to take place, but saliva will continue to act for a time even when food is passed into the stomach. The tongue is an important component in the mouth as it: 1) mixes food with saliva, 2) rolls the food into a bolus and 3) helps in swallowing it. 1st part of swallowing 2nd part of is voluntary swallowing is involuntary Ms R. M. Azzopardi 14 1. The action of salivary amylase on starch Saliva from a water-cleaned mouth is collected in two test-tubes, labelled A and B. The saliva is then heated in tube B over a small flame until it boils for about 30seconds and then the tube is cooled under the tap. 2mL of starch solution is added to each test tube and left for about 5 minutes. The contents of both tubes A and B were shared into two separate test tubes. Some iodine solution was then added to one test tube from sample A and another from sample B and Benedict’s solution was added to the other test tubes from sample A and B. Results: The contents of tube A fail to give a blue colour with iodine, showing that the starch has gone. The other half of the contents, however, gives a red or orange precipitate with Benedict’s solution, showing that sugar is present. The contents of tube B still give a blue colour with iodine but do not form a red precipitate on heating with Benedict’s solution. Ms R. M. Azzopardi 15 Interpretation The results with tube A suggest that something in saliva has converted starch into sugar. The fact that the boiled saliva in tube B fails to do this, suggests that is an enzyme in saliva which brought about the change, because enzymes are proteins and are destroyed by boiling. If the boiled saliva had changed starch to sugar, it would have ruled out the possibility of an enzyme being responsible. 2. The action of pepsin on egg-white protein A cloudy suspension of egg-white is prepared by stirring the white of one egg into 500cm3 tap water, heating it to boiling point and filtering it through glass wool to remove the larger particles. Label four test-tubes A, B, C and D and place 2cm3 egg-white suspension in each of them. Then add pepsin solution and/or dilute hydrochloric acid to the tubes as follows: A Egg-white suspension + 1cm3 pepsin solution (1%) B Egg-white suspension + 3 drops dilute hydrochloric acid (HCl) C Egg-white suspension + 1cm3 pepsin + 3 drops HCl D Egg-white suspension + 1cm3 boiled pepsin + 3 drops HCl Ms R. M. Azzopardi 16 Place all four tubes in a beaker of warm water at 35˚C for 10-15minutes. Result The contents of tube C go clear. The rest remain cloudy. Interpretation The change from a cloudy suspension to a clear solution shows that the solid particles of egg protein have been digested to soluble products. The failure of the other three tubes to give clear solutions shows that: Pepsin will only work in acid solutions It is the pepsin and not the hydrochloric acid which does the digestion Pepsin is an enzyme because its activity is destroyed by boiling. 3. The action of lipase Place 5mL milk and 7mL dilute (M/20) sodium carbonate solution in each of three test-tubes labelled 1 to 3 in the figure below. Add 6 drops of phenolphthalein to each to turn the contents pink. Add 1mL of 3% bile salts solution to tubes 2 and 3. Add 1mL of 5% lipase solution to tubes 1 and 3, and an equal volume of boiled lipase to tube 2. Result In 10 minutes or less, the colour of the liquids in tubes 1 and 3 will change to white, tube 3 changing first. The liquid in tube 2 will remain pink. Ms R. M. Azzopardi 17 Interpretation Lipase is an enzyme that digests fats to fatty acids and glycerol. When lipase acts on milk fats, the fatty acids produced react with the alkaline sodium carbonate and make the solution more acid. In acid conditions, the pH indicator, phenolphthalein, changes from pink to colourless. The presence of bile salts in tube 3 seems to accelerate the reaction, since they emulsify (increase the surface area of the fat) although bile salts with the denatured enzyme in tube 2 cannot bring about the change on their own. Digestion in the stomach This part of the alimentary canal has elastic walls and so can be extended as the food accumulates in it. This enables the food from a meal to be stored for some time and released slowly to the rest of the alimentary canal. Very little absorption takes place in the stomach, but its glandular lining produces gastric juice containing the enzyme pepsin, and it may also contain an enzyme called rennin, young children. Pepsin acts on proteins and breaks them down into more soluble compounds called peptides. Rennin, if present, clots protein in milk. The stomach wall also secretes hydrochloric acid (HCl) which makes a 0.5% solution in the gastric juice. The acid provides the best degree of acidity (optimum pH of 2) for pepsin to work in, and probably also kills many of the bacteria taken in with the food. The salivary amylase from Ms R. M. Azzopardi 18 the mouth cannot digest starch in acid atmosphere but is seems likely that it continues to act within the bolus of food until this is broken up and the hydrochloric acid reaches all its contents. pepsinogen pepsin Hydrochloric acid (pH 2) protein peptides pepsin The rhythmic, peristaltic movements of the stomach, about every 20seconds, help to mix the food and gastric juice to a creamy fluid called chyme. Each wave of peristalsis also pumps a little of the chyme from the stomach into the first part of the small intestine, called the duodenum. The pyloric sphincter is usually relaxed but contracts at the end of each wave of peristalsis, so limiting the amount of chyme which escapes. Even when relaxed, the pyloric opening is narrow and only liquid is allowed through. When the acid contents of the stomach enter the duodenum, they set off a reflex action, which closes the pyloric sphincter until the duodenal contents have been partially neutralized. A meal of carbohydrates such as porridge may be retained less than an hour, and a mixed meal containing proteins and fat may be in the stomach for one to two hours. Ms R. M. Azzopardi 19 Small intestine The small intestine is made up of two parts, duodenum (the first part of the intestine), and the ileum (the second longer part of the intestine). Nearly all the absorption of digested food takes place in the ileum, which is efficient at this for the following reasons: The ileum is long and presents a large absorbing surface to the digested food. Its internal surface is greatly increased by circular folds having thousands of villi (tiny projections). These villi are about 0.5mm long and look finger-like. The lining epithelium is very thin and the fluids can pass rapidly through it. The outer membrane of each epithelial cell has microvilli which increase by 20 times the exposed surface of the cell. There is a dense network of blood capillaries (tiny blood vessels) in each villus. Between each villus are crypts which secrete mucus for the protection of the outer layer of the intestine and replace lost crypt epithelial cells. Ms R. M. Azzopardi 20 Digestion in the duodenum and the ileum An alkaline juice from the pancreas, and bile from the liver, are poured into the duodenum. The pancreas is a cream-colour gland lying below the stomach. Its cells make enzymes which act on carbohydrates, proteins and fats respectively. Three of these enzymes, including trypsin, break down proteins to peptides, and peptides to soluble amino acids. Starch is broken down to maltose by amylase, and fats are split up into fatty acids and glycerol by lipases. Trypsin: proteins peptides amino acids Pancreatic amylase: starch maltose Lipase: fats (lipids) fatty acids + glycerol Pancreatic juice also contains sodium hydrogen carbonate which partly neutralizes the acid chyme from the stomach, and so creates a suitable environment (pH) for the pancreatic and intestinal enzymes to work in. Bile is a green, watery fluid made in the liver, stored in the gall bladder and conducted to the duodenum by the bile duct. Its colour is derived largely from breakdown products of the red pigment form decomposing blood cells. It contains sodium chloride and hydrogen-carbonate, and organic bile salts but no enzymes. Bile dilutes the contents of the intestine, and the bile salts reduce the surface tension of fats, so emulsifying them. This results in fats forming a suspension of tiny droplets, the increased surface so presented allowing more rapid digestion. Many of the bile salts are reabsorbed in the ileum. Ms R. M. Azzopardi 21 For the small intestine to protect itself from all the protein-digesting enzymes (proteases) which it secretes, it must secrete these proteases in an inactive form. Pepsin is produced as pepsinogen, and doesn’t become activated until it encounters the hydrochloric acid in the stomach. The lining of the stomach is protected from the action of pepsin by the thick layer of mucus on top of it. Likewise, trypsin which is a protease secreted from the pancreas, is secreted in the inactive trypsinogen and is activated by enterokinase, which is an enzyme secreted by the duodenum. In the stomach: pepsinogen pepsin Hydrochloric acid (pH 2) In the small intestine: trypsinogen trypsin enterokinase Proteins trypsin polypeptides Polypeptides erepsin amino acids Starch maltose Pancreatic amylase Fat fatty acids + glycerol lipase In the small intestine, digestion is continued by the action of the pancreatic enzymes. All the digestible material is changed to soluble compounds which pass into the cells lining the ileum. In these cells, peptides are broken down to amino acids, and maltose and sucrose are broken down to glucose and fructose. These substances then enter the blood capillaries, where they are then Ms R. M. Azzopardi 22 processed inside the cell to make use of them such as in respiration, a process called assimilation. After that all the substances have been absorbed, are then transported by the blood via the hepatic portal vein to the liver which may either store some of the digested products (such as glucose and convert it into glycogen) or else is transported in a vein (vena cava) to the heart. A large portion of the fatty acids and glycerol may be combined to form fats again in the lacteals (lymph vessels). The fluid in the lacteals flows to the lymphatic system, which forms a network all over the body and eventually empties its contents into the bloodstream. Some ions are transported by diffusion and by active transport. Ms R. M. Azzopardi 23 Caecum and Appendix In some grass eating animals (herbivores), such as rabbits, horses and cows, the caecum and appendix are quite large. It is in these organs that digestion of plant cell walls takes place, largely because of bacterial activity. In humans, the caecum and appendix are small structures, possibly without digestive function. The appendix, however, contains lymphoid tissue and may have an immunobiological function. The large intestine (colon and rectum) The material passing into the large intestine consists of water with undigested matter, largely cellulose and vegetable fibres (roughage), mucus and dead cells from the lining of the alimentary canal. The large intestine secretes no enzymes but the bacteria in the colon digest part of the fibre to form fatty acids which the colon can absorb. Bile salts are absorbed and returned to the liver by the blood circulation. The colon also absorbs much of the water from the undigested residues. About 7 litres of digestive juices are poured into the alimentary canal each day. If the water from these was not absorbed by the ileum and colon, the body would soon be dehydrated. The semi-solid waste, the faeces or ‘stool’, is passed into the rectum by peristalsis and is expelled at intervals through the anus. The residues may spend from 12 to 24 hours in the intestine. The act of expelling the faeces is called egestion or defecation. Ms R. M. Azzopardi 24 Use of digested food The products of digestion are carried round the body in the blood. The process of assimilation is the process by which the soluble substances are absorbed in the blood, and are then manufactured and transformed into other substances inside cells. Glucose: used during respiration in the cells, glucose is oxidized to carbon dioxide and water. This reaction provides energy to drive other chemical reactions to contract and relax muscles, conduct electrical impulses, and build-up of proteins. When glucose is not required immediately, it is converted to insoluble glycogen by adding lots of glucose molecules together, and glycogen is then stored in the liver. When the blood sugar falls below a certain level, the liver changes its glycogen back to glucose and releases it into the circulation. The muscle glycogen isn’t returned to the circulation but is used by muscle cells as a source of energy during muscular activity. Glycogen in the liver is a ‘short-term’ store, sufficient for only about 6hours. Excess glucose not stored in the fat depots. Ms R. M. Azzopardi 25 Fats: are built into cell membranes and other cell structures. Fat also form an important source of energy for cell metabolism. Fatty acids produced from stored fats, taken in with the food, are oxidized in the cells to carbon dioxide and water. The releases energy for processes such as muscle contraction. Fats can provide twice as much energy as sugars. Unlike glycogen, there is no limit to the amount of fat stored and because of its high energy value it is an effective ‘long-term’ store. The fat is stored in adipose tissue in the abdomen, round the kidneys and under the skin as fat depots. Some cells accumulate drops of fat in their cytoplasm. As these drops increase in size and number, they join to form one large globule of fat in the middle of the cell, pushing the cytoplasm into a thin layer and the nucleus to one side. Amino acids: are absorbed by the cells and built up, with the aid of enzymes, into proteins. Some of the proteins will become plasma proteins in the blood. Others may form structures such as the cell membrane or they may become enzymes which control the chemical activity within the cell. Amino acids not needed for making cell proteins are converted by the needed for making cell proteins are converted by the liver into glycogen which can then be used for energy. Amino acids aren’t stored in the body. Those not used in protein formation are deaminated. The protein of the liver and other tissues can act as a kind of Ms R. M. Azzopardi 26 protein store to maintain the protein level in the blood, but absence of protein in the diet soon leads to serious disorders. Ms R. M. Azzopardi 27 Region of Digestive Digestive juice Enzymes in Class of food Substances alimentary Notes gland produced the juice acted upon produced canal Salivary Mouth Salivary glands Saliva Starch Maltose Slightly acid or neutral amylase 0.5% hydrochloric acid also secreted, Gastric glands Pepsin Proteins Peptides provides acid medium for pepsin and kills Stomach (in stomach Gastric juice most bacteria. No absorption except of lining) (Rennin) (milk protein) (Clots it) alcohol Protein and Trypsin Amino acids Two other protein-digesting enzymes are peptides Pancreas Pancreatic juice present. Bile emulsifies fats and aids their Duodenum Amylase Starch Maltose (Liver) (bile) absorption. Duodenum contents are slightly Fatty acids Lipase Fats acid. and glycerol Pancreatic Peptides Amino acids The glands Intestinal juice enzyme are Fatty acids These final stages of digestion take place in Fats between the contains an still active + and glycerol the ileum with the aid of pancreatic villi produce enzyme which Maltase Maltose Glucose enzymes. Some digestion occurs in the Ileum mucus but few, activates Sucrose Glucose and epithelial cells of the villi. Sucrose if any, digestive pancreatic Lactase fructose The main function of the ileum is the enzymes trypsin Erepsin Glucose and absorption of the digested products. Lactose Enterokinase galactose Colon Bacterial enzymes produce fatty acids from vegetable fibre Absorption of water Mrs R. M. Azzopardi 28