Cell Metabolism.docx

Cell Metabolism Metabolism is the sum of all the chemical reactions taking place in a cell or organism. All the reactions that occur in the cell either produce or use energy. Almost all the energy required by cells comes directly or indirectly from the sun. Plants Use light energy from the sun and c...

Cell Metabolism Metabolism is the sum of all the chemical reactions taking place in a cell or organism. All the reactions that occur in the cell either produce or use energy. Almost all the energy required by cells comes directly or indirectly from the sun. Plants Use light energy from the sun and chlorophyll to produce glucose and oxygen from carbon dioxide in a process called photosynthesis. - Glucose can be used in cellular respiration to produce Adenosine triphosphate (ATP). - Glucose can be converted into other compounds needed by the plant. Animals When animals eat plants, they digest the plant material. Products of digestion are glucose and amino acids. - Glucose is respired by cells to produce ATP to supply their immediate energy needs. Leftover glucose can be converted to glycogen and stored. - Amino acids obtained from the plants can be joined together to form animal proteins and build muscle and bone. Excess amino acids are broken down to urea and secreted in urine by the kidneys. Enzymes **Need to Know** -Enzymes are proteins and biological catalysts that speed up chemical reactions without being used up by the cell. Enzymes are specific, which means they only work on one substrate, producing one set of products. -Enzymes are made of long chains of amino acids joined together by peptide bonds. The chains of amino acids that form the enzyme are folded into a complex 3D shape. - Some enzymes need helper chemicals to attach to them in order to work properly. These helper substances are called co-enzymes. Co-enzymes are organic, non-protein molecules. Some vitamins, such as B1 and B6, act as co-enzymes. - Names for enzymes end in ‘ase’. Factors affecting enzyme activity**Be able to explain both** Enzymes are sensitive to their environmental conditions and can be seriously affected by pH and temperature. They are also affected by enzyme concentration, substrate concentration and the presence of inhibitors. - pH: Different enzymes work best within certain narrow pH ranges. Most work best at around neutral (amylase, pH 7). Pepsin, which is releases in the stomach to act on proteins, works best at around pH 2. Lipase works in the small intestine digesting fats and acts best at pH 10. - Temperature: Enzyme activity increases with temperature, up to around 40oC. Above 40oC enzymes rapidly denature (change shape) and do not work. The human temperature of 37oC is close to the optimum temperature, but it is also close to the temperature at which enzymes start to denature. If your temperature gets too high, enzymes are affected, particularly in the brain. This can cause seizure and fits. Plant enzymes prefer an optimum temperature of around 25oC. Denatured Enzymes Denatured means that an enzyme has lost its shape and therefore its activity. There are three main causes of enzymes/proteins becoming denatured. - Temperature above 40oC: At temperatures just above 40oC, the enzyme begins to lose its shape and its activity. If the temperature drops back down below 40oC, it will resume its shape and activity. Once the temperature rises above 50oC, the change becomes irreversible. For example, Albumen, a major constituent of egg whites, starts off as a clear runny jelly, but when denatured it becomes stiff and white. - Change in pH: Salivary amylase acts on starch in the mouth and begins the process of breaking it down into fructose. Optimum pH is 7—8 which is what is found in the mouth. Once the food reaches the stomach, the pH suddenly changes to a very acidic pH 1, which denatures the salivary amylase and stops carbohydrate digestion. Food, like beetroot, can be pickled by placing it in an acid medium (vinegar). The pH is around 3 and this denatures the enzymes in bacteria and fungi so they cannot survive. Benzoic acid preserves soft drinks. - Agitation: Shaking/beating can denature enzymes. When egg whites are beaten with sugar, the albumen is denatured to form microscopically small strands of solid protein that trap and bind the sugar. This makes it thick and viscous so that it can be shaped. Active Site Theory Active site is the place on the enzyme where its substrate fits and where the reaction takes place. The shape is so precise that only one substrate can fit. - As the substrate engages with the active site, its shape changes slightly and in many cases the shape of the enzyme also changes a little. The combination of the enzyme and the substrate is called the enzyme-substrate complex. - These changes make it easier for the products to form, lowering the activation energy. The products form a substrate-product complex from which the products are ejected. This allows the enzyme to regain its original shape and thus become free to collect a fresh substrate molecule. - If the product is more complex than the reactants, it is an anabolic reaction. Making muscle is anabolic. - If the products are smaller and less complex than the reactant, it is a catabolic reaction. Digestion is catabolic. (1) Bioprocessing Bioprocessing is the use of living organisms or their products to produce useful substances. Bioprocessing uses yeast to make bread and alcohol. Microorganisms are used to produce yoghurt and cheese. Microorganisms are used in sewage treatment to make sewage biologically safe. Genetically modified examples include insulin and antibiotics. Bioprocessing Methods A bioreactor is a vessel in which cells or organisms make products. - Batch: Raw materials and immobilised enzymes or their sources are placed in the bioreactor and allowed to react. When the reaction is complete, the products are removed, separated, and purified if needed. The bioreactor is cleaned, and another fresh batch is prepared. This method allows greater quality control. Examples include antibiotics, yoghurt, cheese, and insulin. (2) - Continuous: In this process, raw materials are fed in at one end and the product comes out the other end over a long period of time. This is a more efficient and quicker process than the batch method. Alcohol can be made this way. (3) Immobilising Enzymes Immobilised means that the enzymes of organisms are trapped in a gel or fixed to each other. This is one of the biggest advances in bioprocessing. Advantages - The enzyme can be reused so only small amounts are needed - The enzyme is easier to recover so it can be used again - It is easier to purify the product as there is one less thing to remove - It makes the enzyme last longer Applications**Know two** - Using immobilised yeast to produce the enzyme zymase to convert sugars, including glucose (substrate) to alcohol (product). - Using invertase (enzyme) to convert sucrose or cane sugar (substrate) to fructose and glucose (product), which is sold as golden syrup. Mandatory Practical – Investigate the effect of pH on the rate of catalase reaction Substrate: 20-volume Hydrogen Peroxide - Use a cork borer to cut out sticks of potato tissue, use a backed blade to cut thin slices. Place into groups of 10. - Place 10cm3 of the substrate hydrogen peroxide into a 50cm3 measuring cylinder and add three drops of washing up liquid. Stir gently to mix. - Add 2cm3 of pH 8 buffer solution to keep the pH constant, stir gently. - Place the measuring cylinder into a water bath and allow the temperature to come to 37oC. - Add 10 potato discs to the cylinder and let it sit for two minutes - Bubbles of oxygen gas are produced and these cause foam to be produced rising up the cylinder - The equation for the reaction is 2H2O2 = 2H2O + O2 - The faster the reaction, the higher the column of foam will rise in a set period of time - Repeat the steps at a different pH (4, 6, 8 and 20) using buffer solutions - Concentration of all reactants is kept constant by using the same amount of hydrogen peroxide, catalase solution, washing up liquid, and buffer solution Mandatory Practical – Investigate the effect of temperature on the rate of catalase reaction - Use a cork borer to cut out sticks of potato tissue, use a backed blade to cut thin slices. Place into groups of 10. - Place 10cm3 of the substrate hydrogen peroxide into a 50cm3 measuring cylinder and add three drops of washing up liquid. Stir gently to mix. - Add 2cm3 of pH 8 buffer solution to keep the pH constant, stir gently. - Place the measuring cylinder into a water bath and allow the temperature to come to 37oC. - Add 10 potato discs to the cylinder and let it sit for two minutes - Bubbles of oxygen gas are produced and these cause foam to be produced rising up the cylinder - The equation for the reaction is 2H2O2 = 2H2O + O2 - The faster the reaction, the higher the column of foam will rise in a set period of time - Repeat the steps at different temperatures (30oC, 40oC, 50oC, 60oC) - Concentration of all reactants is kept constant by using the same amount of hydrogen peroxide, catalase solution, washing up liquid, and buffer solution Mandatory Practical – Investigate the effect of heat denaturation on activity of an enzyme - Use a cork borer to cut out sticks of potato tissue, use a backed blade to cut thin slices. Place into groups of 10. - Boil 10 of these discs for five minutes and leave the other 10 un-boiled. The un-boiled discs will act as the control for comparison - Add each set of discs to two identical tubes of catalase plus washing-up liquid plus pH buffer (8) as 40oC - Measure the rate of enzyme activity by the height of foam after two minutes - A typical result would be un-boiled = 2cm of foam and boiled = 0cm foam Mandatory Activity – Prepare one enzyme immobilisation and examine its application Immobilising the enzyme - Dissolve sodium alginate in tepid water - Mix the organism yeast with the sodium alginate solution and stir until it is evenly distributed - Extract up some of this solution with a syringe and slowly drip this into a beaker containing a solution of calcium chloride - The drips form beads of insoluble calcium alginate, which sink to the bottom of the beaker - The reaction that turns the sodium alginate into calcium alginate is slow, so you should leave these beads to harden for at least 10 minutes - Once they have hardened, pour the contents of the beaker through a sieve to collect the beads of immobilised yeast and then wash them gently with clean water Using the immobilised enzyme - Place some sucrose solution in a beaker - Add the beads of immobilised yeast (enzyme) to this sucrose solution. - Leave for 10 minutes - Test the solution for glucose using a Clinistix strip or remove some of the solution and test it using Benedict’s solution - As a control, place some beads made in the same way but without yeast into sucrose solution Photosynthesis Photosynthesis is the conversion of light energy to chemical energy using chlorophyll, C2O and H2O. 6CO2 + 6H2O sunlight C6H12O6 + 6O2 carbon water chlorophyll glucose oxygen dioxide (4,5) Leaf Adaptations for Photosynthesis - Stomata: for gaseous exchange. Mostly on lower epidermis. Open during day to allow carbon dioxide in for photosynthesis. Closed at night to reduce transpiration. - Air spaces: These spaces between spongy mesophyll cells allow for diffusion of CO2 and H2O within the leaf. - Thin: Thinness allows for the rapid diffusion of CO2 in, and oxygen out. Also allows all cells to capture light. - Cuticle: prevents excessive water loss, transparent so it allows light through for photosynthesis - Leaf flattened: to give a large surface area for maximum absorption of light and CO2. - Xylem vessels: to bring water for photosynthesis - phloem sieve tubes: to translocate food like sucrose - Petiole: places lamina in best position for light absorption - Palisade mesophyll: has a high cell density and a large number of chloroplasts per cell for maximum photosynthesis Factors affecting rate of photosynthesis The rate of photosynthesis is determined by the factor which is in short supply. This factor is called the limiting factor. The rate can be measured roughly by the amount of CO2 absorbed or O2 released by a plant. - Carbon dioxide: enters through stomata on the lower epidermis and diffuses through the air spaces of the mesophyll. As CO2 increases so does the rate of photosynthesis until it reaches a plateau. For example, crop production in an enclosed greenhouse can be increased by pumping CO2 into the space. CO2 can be a limiting factor when plants are overcrowded on a sunny day. - Light: Light is necessary because it provides the energy needed to convert carbon dioxide and water into glucose. With an increase in light intensity, photosynthesis increases up to light saturation when a plateau is formed. Light may be limiting at dawn, dusk, in a forest, or on a warm but dull day. - Temperature: The optimum temperature for most plant enzymes is 25oC . This is why plants grow better in warm climates, indoors, heated glasshouses, or in summer. Growth of plants is slower in colder months due to lower light intensity (hence lower photosynthesis). Temperature may be a limiting factor in early morning when it is bright but cool. -Water: Water is freely available. It is absorbed by plant root hairs and is conducted through the xylem by the transpiration stream. Light-dependent and Light-independent stages of Photosynthesis Light phase: a photochemical reaction in which light energy is converted into chemical energy in the grana of the chloroplast. Dark phase: Light independent. Sugar is synthesised in the stroma. Reactions are catalysed by enzymes; therefore, the rate is affected by temperature. Light-Dependent Stage Pathway 1 – Cyclic Photophosphorylation - Described as cyclic because the energised electrons that leave the chlorophyll eventually return to the chlorophyll molecule having lost their energy - The chlorophyll absorbs light energy and passes it to an electron, which it then ejects as a high-energy electron - A compound called an electron accepter accepts this high-energy electron and then passes the electron to a series of molecules called the electron transport chain - As the electron passes along the chain, its excess energy is used to produce ATP. By the end of the chain, the electron has lost its excess energy and is now a low energy electron again - The electron returns to the chlorophyll - The ATP produced here is used in the light-independent stage (6) Pathway 2 – Non-Cyclic Photophosphorylation - non-cyclic because the electrons that leave the chlorophyll are replaced by electrons from a different source. The chlorophyll pulls electrons from surrounding water molecules and causes them to break down in a process called photolysis - High energy electrons are passed to the electron transport chain, where they combine ADP and P to form ATP. The ATP is then used to produce glucose in the light-independent stage - The electrons that have passed through the electron transport chain are now low energy and these replace the high-energy electrons that have left the chlorophyll - Oxygen atoms are produced and pairs of these combine to form oxygen gas. This is either used immediately in respiration by the plant, or any excess oxygen diffuses out into the intercellular spaces and from there through the stomata into the atmosphere where it can be used in respiration by other organisms - Hydrogen atoms enter the proton pool. These hydrogen ions are then used in the light-independent stage to combine with CO2 to form glucose. (7) Formation of NADPH - NADP+ that has returned from the light-independent stage picks up two excited electrons that were produced by chlorophyll and held by the electron acceptor. This produces NADP- NADP+ + 2e- = NADP- The NADP- then picks up a hydrogen ion from the proton pool to form NADPH NADP- + H+ = NADPH The NADPH then carries the H to the light-independent stage. Light-independent Stage(Calvin stage) - Carbon dioxide from the atmosphere or from cellular respiration diffuses into the stroma - Hydrogen ions and electrons brought from the light stage by NADPH are added to the CO2 and form the carbohydrate glucose - The NADPH turns back into NADP+. This then returns to the thylakoid membrane to form NADP- again. - Energy for the formation of glucose is supplied by ATP from both the cyclic and non-cyclic pathways of the light-dependent stage - As the ATP breaks down to ADP + P, energy is released - The ADP and P return to the electron transport chain to form more ATP Mandatory Activity – To examine the effect of light intensity on the rate of photosynthesis **Know in Detail** - Obtain a fresh shoot of Elodea. - Cut the stem at an angle. Remove several leaves from the cut end of the stem. - Fill a boiling tube with pond water or add 1% w/v sodium bicarbonate to the boiling tube. - Place the plant into the boiling tube, cut end pointing upwards. - Place this tube into the water bath. - Switch on the light source. - Place the water bath containing the elodea at a measured distance from the light source e.g. 15 cm. - Allow the plant to adjust for at least 5 minutes and observe bubbles being released from the cut end of the stem. - Count and record the number of bubbles released per minute. Repeat twice. - Calculate and record the average number of bubbles released per minute. - Measure the light intensity at this distance using the light meter or calculate the light intensity by using the formula: light intensity = 1/d2, where ‘d’ represents the distance from the light source. Record result. - Repeat the procedure from step 9 at other measured distances e.g., at 30 cm, 45 cm, 60 cm, 75 cm. -A graph should be drawn of rate of bubble production against light intensity. Put light intensity on the horizontal axis. Respiration Respiration is the process of changing chemical energy from food into a form of energy that can be used by cells to carry out their functions. C6H12O6 + 6O 2 → 6H2O + 6CO2 + 2820 kj (plants & animals) There are two types of respiration; - Anaerobic Respiration: Respiration that does not require oxygen and produces small amounts of energy - Aerobic Respiration: The release of energy from organic compounds. It needs oxygen and produces large amounts of energy Metabolism In every living cell of every organism there are millions of chemical reactions occurring all of the time, these reactions are called metabolism. There are two types of chemical reactions involved; - Anabolic Reactions: Build up complex compounds out of elements or out of simpler compounds. They obtain the energy that they need from adenosine triphosphate (ATP). ATP breaks down to adenosine diphosphate (ADP) and an inorganic phosphate. In the process, energy is released. ATP = ADP + P + energy Photosynthesis and protein synthesis are the most common reactions of this type - Catabolic Reactions: Break down more complex molecules into simpler ones and release energy in the process. The energy is used to convert ADP and P into ATP. ADP + P + energy = ATP The breaking of ATP into ADP and P, as well as respiration and digestion, are typical examples. Functions of ATP - Stores the energy released in reactions, such as photosynthesis or respiration, in a form that can be used by cells - Transports the energy around the cell from where it is produced to where it is required The Energy Cycle - Respiration releases energy in the form of ATP. The ATP transfers the energy and once it reaches the location where the energy is required, it releases the energy forming ADP and an inorganic phosphate usually written as P. - The ADP and free phosphate are then available to be reassembled into ATP provided there is energy available. In the formation of ATP, a third phosphate is forced to join ADP. - Forcing the third phosphate requires energy and this energy is stored in the final high-energy bond of the ATP. - Metabolism produces waste materials such as urea, carbon dioxide and water. The removal of these waste products is called excretion. Biochemistry of Respiration Stages of Respiration 1. Glycolysis – Glycolysis means the splitting glucose (6-carbon sugar), into two 3-Carbon molecules, which can be called either pyruvate or pyruvic acid. - Glycolysis occurs in the cytoplasm of the cell and does not require oxygen. It releases a small amount of energy in the form of ATP. For each molecule of glucose, 2 ATP must be used to start the reaction. 4 ATP are produced so there is a net gain of 2 ATP for each glucose molecule broken down. 2a. The Krebs cycle- The pyruvate now enters the matrix/lumen of the mitochondrion where it loses CO2 and 2 Hydrogen atoms. The remaining 2 Carbon, acetyl group, is attached to a carrier molecule, co-enzyme A, to form acetyl coenzyme A. The acetyl group is passed by co-enzyme A into a series of reactions called the Krebs cycle. A 4 Carbon compound bonds to the acetyl group forming a 6 Carbon compound. The co-enzyme A is detached and recycled. This 6 Carbon compound is converted in steps back to the 4 Carbon compound by losing two CO2s and 4 hydrogen pairs. One ATP is also released 2b. Electron Transport Chain – This is the formation of ATP in the cristae using oxygen. The electrons from the 2 Hydrogen atoms are passed along a series of carrier molecules and the energy released in each transfer is used to make ATP. The hydrogen ions and electrons finally unite with oxygen to form water. The water may be used by the cell. Aerobic Respiration This is the breakdown of sugar to release energy in the absence of oxygen. It occurs in some bacteria and most animal cells e.g., muscle cells during strenuous exercise. The product is lactic acid. This reduces the efficiency of the cells. The acidity lowers the pH which slows down enzyme action and causes cramps and stiffness. The deeper and faster breathing at the end of strenuous exercise is needed to convert the lactic acid back into glucose in the liver. The equation for Aerobic respiration is the reverse of the equation for Photosynthesis C6H12O6 + 6O2 = 6CO2 + 6H2O Glucose + Oxygen = Carbon Dioxide + Water Anaerobic Respiration(Fermentation) Fermentation is the anaerobic respiration of sugars. It is an example of biotechnology. Biotechnology is the manufacture of a useful product using living things. Bacteria and fungi are the main organisms used. Plants and animals can also be used. Biological advantages of fermentation: Source of energy in oxygen-deficient environments. Disadvantages: Only 2 ATPs are produced compared to 38 ATPs per glucose in aerobic respiration. Products are also toxic and must be excreted. Uses: Alcohol production, bread making, yoghurt and cheese making Antibiotics, insulin, human growth factor, clotting factors Mandatory Practical – Investigate the production of ethanol by yeast and testing for the presence of ethanol **Need to know in detail** (8) To produce alcohol using yeast: - Prepare 400 ml of a 10% w/v glucose solution. - Into each of the two conical flasks, add 200 ml of the glucose solution. - To one of the conical flasks, add 5g of yeast and swirl. Label this ‘yeast + glucose’. - The second flask acts as a control – it has no yeast. Label this ‘control’. - Half fill two fermentation locks with water. Attach one fermentation lock to each flask. - Place both flasks in an incubator at 30OC overnight. - As fermentation proceeds, bubbles of carbon dioxide are produced and bubble out through the fermentation lock. - Fermentation is complete when no more bubbles of CO2 are produced and when the solution becomes clear as the yeast settles to the bottom of the flask. To show the presence of alcohol: Iodoform test for alcohol: - Remove both flasks from the incubator and filter the contents of each into separate boiling tubes and label as before. Filter until 3 ml of each is collected. - To each boiling tube, add 3 ml of the potassium iodide solution and 5 ml of the sodium hypochlorite solution. - Warm gently for 4-5 minutes in the water bath. - Allow to cool and observe any changes. - Record and compare results. - Replicate the investigation or cross reference your results with other groups. - A yellow precipitate confirms that ethanol is present. Movement through Cell Membranes Diffusion is the movement of molecules from a region of high concentration to a region of low concentration (until the two concentrations are the same). - Diffusion is passive i.e., no energy required. - Rate of diffusion depends on factors such as temperature, concentration difference, distance, surface area, type of medium and mass of substance. - Faster diffusion if the temperature is high, short distance, big concentration difference, gas medium. Examples of diffusion - gaseous exchange in alveoli of lungs - diffusion of oxygen into a cell for respiration and carbon dioxide out of mitochondrion - gaseous exchange in leaf e.g., carbon dioxide for photosynthesis. - the smell of perfume, bread baking and stink bombs - sugar in tea - transpiration of water vapour through stomata of leaf - absorption of food in villi Osmosis is the movement of water molecules from a region of higher water concentration to a region of lower water concentration across a semi-permeable membrane. Examples of Osmosis - water absorption by roots - water movement from cell to cell - water reabsorption by nephron (in kidney) Selectively permeable membranes allow some but not all substances to go through e.g., biological membranes, cellophane, visking tubing, dialysis tubing. They allow substances such as water, oxygen, and carbon dioxide to pass freely but do not allow sugars, proteins, and salts to pass through easily. Turgor or turgor pressure is the pressure of the cytoplasm and vacuole against the cell wall of a plant. A plant cell is turgid (firm) when no more water can enter the cell by osmosis i.e., outward pressure of vacuole (turgor pressure) versus resistance of cell wall. When a cell is fully turgid it can support its own weight. When cells lose turgor a plant wilts as cells become flaccid and cannot support their own weight. Application of High Salt or Sugar Concentration in Food Preservation When jam is made by boiling sugar and fruit, the high temperature reached kills all microorganisms present. The high sugar concentration removes water from any new microorganisms that land on it by osmosis, which results in their death, thus preventing reinfection and preserving the jam. Salting fish and beef kills all microorganisms present by extracting water from them by osmosis. It then kills any new microorganisms that land on it afterwards, in the same way. Mandatory Practical – Demonstrating Osmosis **Know in detail** (9) - Soften two 40 cm strips of visking tubing by soaking them in water. - Tie a knot at one end of each strip. - Using a clean funnel, half-fill one piece of tubing with sucrose solution and the other with distilled water. - Eliminate as much air as possible from the tubes and tie a knot at the open end of each tube. - In the case of each tube, tie the two ends, making a loop. - Wash off any excess sucrose solution from the outside of the sucrose tube and pat dry both tubes with the paper towels. - Observe and record the turgidity of each tube. - Find the mass of each tube and record. - Suspend the tube containing the concentrated sucrose solution, by means of a glass rod, in a beaker of distilled water and label it ‘sucrose solution’. - Similarly, place the tube containing the distilled water into a second beaker of distilled water and label it ‘distilled water’. This acts as the control. - Allow the tubes to stand for at least 15 minutes. - Remove the tubes and dry as before. - Observe and record the turgidity of each tube. - Again, find the mass of each tube and record. - Replicate the investigation or cross reference your results with other groups. Both the mass and turgidity of the Visking tubing containing the concentrated glucose solution will have increased, as deionised water has moved into the glucose solution, demonstrating osmosis. Exam Questions 2014 – HL – Section C – Question 13 13. (a) Study the graphs of enzyme activity below and answer the questions that follow. (i) In the case of each graph state the relationship between the rate of reaction (y-axis) and another factor (x-axis). Graph A – The rate of reaction decreases as the other factor (x-axis) increases Graph B – The rate of reaction increases up to a point and then decreases as the other factor (x-axis) increases (ii) In the case of graph B, what factor could be responsible for the changes in activity of the enzyme? Temperature (b) (i) Give a detailed account of how enzymes work, referring in your answer to their specificity. - Enzymes have an active site - Enzymes are specific – they bind with only one substrate - The enzyme changes the shape of its active site slightly – induced fit - An enzyme-substrate complex is formed - Product is formed - Enzyme and its active site remain unchanged. (ii) Name two processes that occur in plant or animal cells that require the use of enzymes – Respiration and Photosynthesis (iii) Some biological washing powders contain enzymes similar to the ones found in our digestive system. Many of these enzymes are extracted from bacteria. 1. Suggest why such enzymes are included in washing powder. - To digest and break down food stains 2. Why is 40 °C the recommended temperature for these washing powders? - It is the optimum temperature 3. Suggest what would happen to these enzymes in an 80 °C wash. - They would be denatured (c) In the course of your practical studies you immobilised an enzyme and then investigated its activity. You also prepared alcohol using yeast. (i) Draw a labelled diagram of the apparatus you used to prepare alcohol. (ii) Give two advantages of using immobilised yeast cells in the production of alcohol – They can be reused - There is no contamination of the product by the enzyme (iii) How did you test for the presence of alcohol – Iodoform Test - Potassium iodide was added to the filtered product - Sodium hypochlorite was added - The mixture was heated - Appearance of pale yellow crystals indicated presence of alcohol 2012 – HL – Section B – Question 9 9. (a) Answer the following in relation to enzymes. (i) What is their chemical nature? Proteins (ii) Comment upon their molecular shape – Enzymes have a folded shape (b) Answer the following in relation to an investigation that you carried out into the effect of temperature on the rate of enzyme action. (i) Name the enzyme that you used - Catalase (ii) Name the substrate of this enzyme – Hydrogen peroxide (iii) Why was it necessary to keep the pH constant in the course of the investigation? In order to have only one variable (iv) How did you keep the pH constant? Using a pH buffer (v) How did you vary the temperature in the course of the investigation? By using water baths at different temperatures (vi) How did you know that the enzyme was working? By the production for froth (vii) Use the axes below to summarise the results of your investigation. Do this by 1. labelling the axes, 2. drawing a graph to show how the rate of enzyme action varied with temperature. References Biolibretexts.org Newyorktimes.com Wikipedia.com Simplyscience.com Thoughtco.com BYJUS.com BYJUS.com PDST.ie PDST.ie