Boardworks GCSE Additional Science: Biology Enzymes Photo credit: JC Revy / Science Photo Library The image shows a molecular computer graphics image of ribonuclease A, an enzyme involved in the destruction of messenger RNA (mRNA) in the cytoplasm of bacteria. At left is its substrate, shifted away from the active site. Enzymes are biological catalysts, proteins that speed up the rates of reactions within cells. Each enzyme is specific for a particular reaction; interaction occurs (typically as a weak bond) between an active site on the enzyme & a reactant (or substrate) due to the arrangement of mutually attractive groups of atoms. This image displays the molecular surface (blue) & polypeptide chain: colours are used to represent the polarity of constituent amino acids.
Boardworks GCSE Additional Science: Biology Enzymes Teacher notes This true-or-false activity could be used as a plenary or revision exercise on enzymes, or at the start of the lesson to gauge students’ existing knowledge of the subject matter. Coloured traffic light cards (red = false, yellow = don’t know, green = true) could be used to make this a whole-class exercise.
Boardworks GCSE Additional Science: Biology Enzymes Teacher notes This four-stage animation demonstrates the principles of the ‘lock and key’ model. While showing the animation, the specific shape of the active site could be highlighted. Suitable prompts could include: What is special about the shape of the active site? Is the enzyme the ‘lock’ or the ‘key’?
Boardworks GCSE Additional Science: Biology Enzymes Teacher notes This matching activity could be used as a plenary or revision exercise on enzymes. Students could be asked to complete the questions in their books and the activity could be concluded by the completion on the IWB.
Boardworks GCSE Additional Science: Biology Enzymes Teacher notes This four-stage animation shows how competitive and non-competitive inhibitors block the action of enzymes by either binding to, or altering the shape of, their active site.
Boardworks GCSE Additional Science: Biology Enzymes Teacher notes This illustration contains several discussion points relating to items made using enzymes, including: Baby food: Proteases such as trypsin are used to predigest the protein in baby foods. Baking (bread): Fungal enzymes are used to catalyze the breakdown of starch into sugar. The enzymes also produce carbon dioxide gas, which makes the dough rise. Biological detergent (washing powder): Proteases, amylases and lipases are used to remove protein, starch and oily stains from clothes. Brewing (beer): Proteases in barley are released as it is fermented during beer production. The enzymes break-down starch, carbohydrases and proteins, and clarify stored beers. Confectionary (chocolates): Enzymes are used to make soft-centred chocolates. Dairy products (cheese): Rennet (an enzyme from calves’ stomachs) is used to coagulate milk during cheese production, separating the curd (solids) from the whey (liquid). Lipases are used to enhance the flavour and ripening of blue cheeses, and lactases are used to break down-lactose into glucose and galactose. Fruit juice: Enzymes that act on cellulose reduce the cloudiness of fruit juices. Paper (penicillin box): Proteases and cellulases are used to soften and smooth pulped fibres during paper manufacture Photography: Proteases are used to dissolve gelatin from waste film, allowing its silver content to be recovered and recycled. Rubber (place mat in high chair): Catalase is used to convert latex into foam rubber.
Boardworks GCSE Additional Science: Biology Enzymes Teacher notes This three-stage animation shows how enzymes are used in breadmaking. Suitable prompts could include: What happens to the amylase and invertase during the baking process? What is the name of the gas that the yeast produce during fermentation?
Boardworks GCSE Additional Science: Biology Enzymes Teacher notes This activity could be used as a precursor to a wider discussion on drugs use and abuse. See the GCSE Science (Biology) ‘ Drug Use and Abuse ’ presentation for more information on alcohol.
Break down of food in the digestive system <ul><li>L/O: </li></ul><ul><ul><li>To understand what a digestive enzyme is, how it works and how they assist with the uptake of the essential nutrients. </li></ul></ul>
Starch molecules – large and branched Amylase – digestive enzyme Breaks down starch to Maltose Still too big! Maltase in the small intestine breaks down maltose to glucose units Readily absorbed.
Breaks down proteins into peptides. Still too big! Proteins – large and branched Trypsin from the pancreas Peptidase from the small intestine
Bile from the liver mixes with the ‘fat’ to make an emulsion Lipase from the pancreas breaks down the fats to... Fatty acids and glycerol which is easily absorbed. Fats & Oils
What are enzymes made of? Enzymes are protein molecules, and so are made up of amino acids . Most enzymes contain between 100 and 1,000 amino acids. These amino acids are joined together in a long chain, which is folded to produce a unique 3D structure.
Why is shape important? The shape of an enzyme is very important because it has a direct effect on how it catalyzes a reaction. An enzyme’s shape is determined by the sequence of amino acids in its structure, and the bonds which form between the atoms of those molecules. Why do enzymes have different shapes? Different types of enzymes have different shapes and functions because the order and type of amino acids in their structure is different.
Why are enzymes so specific? Enzymes are very specific about which reactions they catalyze. Only molecules with exactly the right shape will bind to the enzyme and react. These are the reactant , or substrate, molecules. The part of the enzyme to which the reactant binds is called the active site . This is a very specific shape and the most important part of the enzyme.
What happens at the active site? In the same way that a key fits into a lock, so a substrate is thought to fit into an enzyme’s active site. The enzyme is the lock , and the reactant is the key . ↔ ↔ enzyme reactant + enzyme-reactant complex ↔ products enzyme + ↔ + +
Digestion in the stomach When food enters the stomach it stimulates the secretion of hydrochloric acid (HCl) from the stomach wall. HCl increases the acidity of the stomach to about pH2 – the optimum pH for stomach enzymes. oesophagus duodenum mucus cells parietal cells (acid-producing) gastric gland
Digestion in the small intestine The liver produces bile (an alkali), which is stored in the gall bladder and released into the small intestine. Bile neutralizes the acidic contents coming from the stomach, creating the alkaline environment that the intestinal enzymes need to work. Digestive enzymes found in the small intestine are damaged by a strongly acidic pH. How does the body avoid this problem? gall bladder duodenum bile duct pancreas hepatic duct
Factors affecting enzymes The rate of enzyme–catalyzed reactions depends on several factors. What are some of these? All enzymes work best at only one particular temperature and pH: this is called the optimum . Factors that affect the rate of a reaction include: <ul><li>substrate concentration </li></ul><ul><li>temperature </li></ul>Different enzymes have different optimum temperatures and pH values. <ul><li>pH </li></ul><ul><li>enzyme concentration </li></ul><ul><li>surface area </li></ul><ul><li>pressure. </li></ul>
Factors affecting enzymes If the temperature and pH changes sufficiently beyond an enzyme’s optimum, the shape of the enzyme irreversibly changes. This affects the shape of the active site and means that the enzyme will no longer work. When this happens the enzyme is denatured . normal denatured heat pH
Enzymes in the home How many items are made using enzymes?
Confectionary A type of enzyme called isomerase converts the sugar glucose into fructose, another type of sugar. Fructose is sweeter than glucose, so a smaller amount is needed. This makes fructose syrup a useful ingredient in slimming foods. Invertase is used to create soft-centered chocolates. The centre initially contains sucrose (cane sugar) and is hard. The invertase breaks down the sucrose into the simpler sugars glucose and sucrose, making the centre soft and runny.