AQA B3 - Organisation and the digestive system

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which includes: ● Mouth - physically breaks down food into smaller pieces ● Salivary glands - produces saliva that contains enzymes • Oesophagus - tube that food travels down to the stomach Liver - releases bile into small intestine where helps to digest fats Stomach food is churned with acids and enzymes Pancreasusing bile ● Small intestines - small soluble molecules absorbed into bloodstream, muscular tissue to physically push material along, where water passes back to the body leaving solid waste Large intestines - main site of water absorption Rectum - faeces stored here before passed out Anus - muscular ring through which faeces passes out the body The digestive enzymes Amylase - breaks down carbohydrates into simple sugars. Is used in the pancreas, small intestine, saliva glands. Protease - breaks down protein into amino acids. Is used in the pancreas, small intestine, stomach. Lipase - breaks down lipids to become glycerol and fatty acids. Is used in the pancreas, small intestine. Bile - is not an enzyme but it increases pH for lipase to work effectively, it emulsifies lipids to increase surface area for enzyme/lipase to work on. Stored in the gallbladder. The pancreas and small intestine produces three enzymes: lipase, amylase, protease. The chemistry of food The structure of a cell is made of carbohydrates, lipids and proteins meaning that they are vital components of a diet, they are all large molecules that are made of smaller molecules joined together as a part of the cell metabolism. Carbohydrates Used for: Provide us with fuel Make all other reactions of life possible Contain chemical elements carbon, hydrogen, oxygen Used in cellular respiration to provide energy for other metabolic reactions All carbohydrates are made up of units of sugars: Best known single sugar is glucose (C6H1206) some carbohydrates are made of two sugar units e.g sucrose, the small carbohydrate units are called simple sugars • Complex carbohydrates e.g starch, cellulose, made of long chains of simple sugars units bonded together Examples of carbohydrates are bread, potatoes and rice. Most carbohydrates will be broken to glucose. Lipids Used for: Fats and oils Efficient energy store and source of energy • Important in cell membranes, hormones and nervous system ● Made of carbon, hydrogen, and oxygen ● Insoluble in water Made up of: ● Three molecules of fatty acids joined to a molecule of glycerol (this molecule can vary) Examples of lipids are olive oil, butter and cheese Proteins Used for: • Building up the cells and tissues of the body Basis for all the enzyme activity • Structural components of tissues e.g muscles and tendons Hormones e.g insulin Antibodies destroy pathogens, part of immune system Enzymes - act as catalysts Made up of: Carbon, hydrogen, oxygen, nitrogen Long chains of amino acids (there around approx. twenty different ones) joined together by special bonds Different arrangements of amino acids determines different proteins Proteins as enzymes: Make specific 3D shapes that enable other molecules to fit into the protein Bonds hold proteins sensitive to temperature, pH so can easily be broken If broken, shape is lost and may not function any more ● Protein denatured Examples of proteins are meat, fish, pulses ● Catalysts and enzymes Enzymes are catalysts, a catalyst speeds up a chemical reaction but it is not used up in the reaction. Enzymes - biological catalysts The rate of chemical reactions is controlled by enzymes (a biological catalyst) that interacts with a particular substrate. Enzymes are large protein molecules made to specific shapes which are vital to function. The long chains of amino acids are folded to produce a molecule with an active site that has a unique shape so it can bind to a specific substrate molecule. How do enzymes work The lock and key theory is a model of how enzymes work. 1. Substrate fits into active site of enzyme 2. Enzyme and substrate bind together 3. Reaction takes place 4. Products released from surface of enzyme (substrate splits into products which leave active site) Enzymes can join small molecules together or break large ones. Metabolic reactions Enzymes control the metabolism (the sum of all the reactions in the body), different enzymes catalyse specific types of metabolic reactions: Building large molecules from smaller ones - e.g starch, glycogen, cellulose from glucose or lipids from fatty acids or proteins from amino acids. Plant cells combine carbon dioxide and water to make glucose and added to nitrate ions to make amino acids • • Changing one molecule into another - e.g changing one simple sugar to another e.g glucose to fructose, and converting one amino acid to another Breaking down large molecules into smaller ones - e.g carbohydrates, lipids, proteins to constituent molecules in digestion, glucose in cellular respiration, excess amino acids to form urea Every cell can have chemical reactions occurring at any time; each of the different types of reaction is controlled by a different specific enzyme. Enzymes deliver the control that makes it possible for the cell chemistry to work without one reaction interfering with another. Factors affecting enzyme action Effect of temperature on enzyme action The rate of enzyme-controlled reactions increases as the temperature increases although at 40°C the protein structure of the enzyme is affected by the high temperature. The chains of amino acids unravel and the shape of the active site changes so the substrate will no longer fit; the enzyme is denatured. So, it cannot act as a catalyst, the rate of reaction drops. Most enzymes work best at 37°C, body temperature. It is dangerous if body temperature goes too high as enzymes will denature and die. Although not all enzymes work best at 40°C, bacteria (in hot springs) survive at 80°C and higher and some can live in the very cold at 0°C and below. Effect of pH on enzyme action The shape of the active site comes from forces between the protein molecules, the forces holding the folded chain in place. A change in pH affects these forces and changes the shape of the molecule. So, the specific shape of the active site is lost and the enzyme no longer acts as a catalyst. Different enzymes work best at varying pH levels and a change in pH can stop them working completely. How the digestive system works Digestive enzymes Enzymes are produced by specialised cells in glands (salivary glands, pancreas) and lining of the digestive system. They operate outside of the cells and control the rate of chemical reactions. They go into the digestive system and come into contact with food molecules The digestive system is a hollow, muscular tube that squeezes food; helps break up food into small pieces that have a large surface area for enzymes to work on; mixes food with digestive juices, enzymes come into contact with as much food as sible; muscles move food along; different areas have different pH levels to let enzymes work as efficiently as possible. Small intestine and mouth - slightly alkaline, stomach acidic pH. Digesting carbohydrates Carbohydrases break down carbohydrates, this reaction is catalysed by an enzyme called amylase. Amylase is produced in the salivary glands, pancreas which travels to the small intestine. Digesting proteins Proteases break down proteins. Protesease are produced by the stomach, pancreas and small intestine. The breakdown of proteins into amino acids takes place in the stomach and small intestine. Digesting fats Lipids are broken into fatty acids and glycerol (in the small intestine), this reaction is catalysed by lipase enzymes which are made in the pancreas (passes to the small intestine), small intestine. Once the food molecules have been digested into soluble glucose, amino acids and fatty acids, and glycerol, they leave the small intestine, pass into the bloodstream to be carried to the cells that need them. Making digestion efficient Changing pH in the digestive system Proteases work best in acidic conditions so the stomach produces a concentrated solution of hydrochloric acid from the same glands which allows protease to work very effectively and kills most of the bacteria that is taken in with the food. Stomach produces a thick layer of mucus which coats the stomach walls and protects them from being digested by acid and enzymes. Food leaves the stomach and goes to the small intestine, some of the enzymes that catalyse digestion in the small intestine are made in the pancreas which work best in an alkaline environment. Acidic liquid coming from the stomach needs to become alkaline in the small intestine so the liver makes bile which is stored in the gallbladder. Bile is squirted onto food coming from the stomach to the small intestine in the bile duct. The bile neutralises the acid and provides alkaline conditions so that enzymes can work most effectively in the small intestine. Altering the surface area It's important for enzymes to have the largest possible surface area of food to work on (not a problem with carbohydrates and proteins). Fats do not mix with watery liquids so stay as large globules which makes it difficult for lipase enzymes to act. Bile emulsifies the fats in food; physically breaks up large drops of fat into smaller droplets to provide a bigger surface area of fats for lipase enzymes to act upon. The larger surface area helps lipase chemically break down the fats more quickly into fatty acids and glycerol. Liver and gallbladder → bile duct → pancreatic duct (from pancreas) → duodenum