Macromolecules (with Lab Simulation)

Chemistry. Introduction to macromolecules, organic molecules abundant in living systems. Notification: If you have a disability that makes it difficult to complete this lab, please contact your instructor. Please provide your instructor a copy of the Memorandum of Accommodation (MOA) from NVCC Disability Support Services. Objectives:____________________________________________________________ • Describe the basic structures and properties of monomers and polymers of carbohydrates, proteins and lipids. • Identify reagents and positive test results for simple sugar, starch, proteins and lipids • Explain how to determine nutritional components of foods based on biochemical analysis Background:__________________________________________________________ All of chemistry is divided into two sections: organic chemistry and inorganic chemistry. Basically, organic chemistry deals with carbon compounds and inorganic chemistry is everything else. Organic compounds come in many different forms, in this lab we will analyze three of them: carbohydrates, lipids, and proteins. Each of these classes is vital to living things. Each also contains numerous different chemicals of various levels of complexity. Carbohydrates Carbohydrates are organic molecules consisting of only carbon, oxygen and hydrogen atoms bonded together. Carbohydrates are energy molecules. They are the fuel that our bodies burn to maintain life. Sugars containing one glucose-like molecule are called monosaccharides from Greek and Latin words meaning “one sugar”. Similarly sugars containing two glucose-like molecules are called disaccharides meaning “two sugars”. Starches are composed of many of these small sugar molecules joined together and are technically called polysaccharides (“many sugars”). In a more general sense the glucose-like molecules can be considered monomers – “one part” – and the long chains polymers – “many parts”. Therefore starch is a polymer, and so are most of the other organic molecules we will be looking at in this lab. These polymers are formed by a process known as dehydration synthesis (or condensation synthesis) – “putting together by removing water.” This can be visualized by the following equation: In today’s lab, you will be testing for the presence of carbohydrates with two separate chemical reagents: iodine and Benedict’s solution. Iodine will stain starch (a complex carbohydrate) a dark blue or black color and Benedict’s will turn green, yellow, orange or red in the presence of various concentrations of simpler sugars (such as glucose). On this scale green indicates a low concentration, red indicates a very high concentration. Proteins Proteins are polymers composed of monomers known as amino acids. There are twenty of these amino acids, each has the -NH2 group at one end and the –COOH group at the other, thus the whole molecule is an amino acid. The R stands for radical group, and can be any of twenty different atoms or atom groups making for the twenty different amino acids. During dehydration synthesis the –OH group from the carboxylic acid end and one of the hydrogens from the amine group are removed and form a water (H2O) molecule. What remains of the two amino acids joins with a peptide bond between the C and the N, forming a dipeptide. This process can continue indefinitely to form a polypeptide. This polypeptide chain is arranged in a complex three-dimensional form that is covered in your lecture text. Changes in this three-dimensional structure may cause the protein to not be able to perform its function. A protein that has been changed in this way is said to be denatured. Proteins perform many functions in living cells. There are structural proteins, storage proteins, transport proteins, contractile proteins, proteins that speed up reactions, proteins that fight infection, proteins that regulate life processes and proteins that detect chemical signals. You will be testing for the presence of peptide bonds or full proteins with Biuret reagent. Biuret will turn purple in the presence of proteins or pink in the presence of smaller peptide fragments. Lipids Lipids are not a single type of molecule; rather, they are various types of organic molecules that are poorly soluble in water. The lipids most familiar to the general public are the fats and oils. While also performing structural duties, their major function is to store energy for later use by the organism. While not really polymers, lipids are still formed via dehydration synthesis between their parts. The fats and oils are composed of glycerol and several fatty acids. Again, dehydration joins the fatty acids to the glycerol through the removal of water to form an ester linkage (an oxygen atom bonded between two carbons). Typical fats and oils have 3 fatty acids attached to the glycerol. All of this may be made clearer by the following diagram showing glycerol, fatty acids and their linkage. The common feature of lipids is that they are hydrophobic, which means they do not mix with water easily. The presence of lipids can be detected by using the Sudan IV reagent, which dissolves more effectively in lipids or fats, forming a red color. The virtual lab you view today uses a simpler test to detect triglycerides, the Grease Spot Test. If lipids are present in a solution applied to paper a translucent spot remains. This is because unlike water the lipids do not absorb enough heat for the air to evaporate and reain within the fibers of the paper. A fourth major type of organic macromolecule consists of nucleic acids. The nature of these molecules will be covered in depth in a later lab. Materials:_____________________________________________________________ • Internet Safety: Follow all standard laboratory safety procedures. Test tubes incubated in the hot water bath will be HOT to the touch. Use the tongs to remove the tubes from the hot water bath. Place hot tubes directly into tube rack. Procedure:___________________________________________________________ Experiment 1. Positive and negative tests for organic molecules Simple Sugars column in the row corresponding to that food sample. If you instead think the food sample does not contain simple sugars, place a “‒” in that column. B. Lab Procedures 1. In the laboratory, you would then obtain the food items. For solid food samples, you would use a razor blade or spatula to obtain a pea sized portion of food. Then, you would place the food sample into a large test tube and add 10ml of water. Next, you would place a clean gloved thumb on top of the test tube and shake vigorously for one minute to break up the food and dissolve as much as possible into the water. The resulting solutions would then be used in your experiments. You would also obtain 5ml of milk in a separate test tube for testing. 2. You would then perform the Benedicts test on each food sample. You would label seven small test tubes, one for each food sample. You would then add approximately 1 mL (or 20-30 drops) of each prepared food sample solution (from step 2 above) to the appropriately labeled test tube. You would next add 5 drops of Benedict’s reagent to each tube. Then, you would incubate all the tubes in a hot water bath for 5 minutes. Based on the color change results and your previous experiments, record whether or not each food sample contains simple sugars in Table 3 of the Lab Worksheet. 3. Next, you would perform the iodine test. Again, you would label seven small test tubes, one for each food sample. You would then add approximately 1 mL (or 20-30 drops) of each prepared food sample solution (from step 2 above) to the appropriately labeled test tube. You would next add 5 drops of Iodine solution to each tube. Based on the color change results and your previous experiments, record whether or not each food sample contains starch in Table 3 of the Lab Worksheet. 4. Then, you would perform the Biuret solution test. Again, you would label seven small test tubes, one for each food sample. You would then add approximately 1 mL (or 20-30 drops) of each prepared food sample solution (from step 2 above) to the appropriately labeled test tube. You would next add 5 drops of Biuret solution to each tube. Based on the color change results and your previous experiments, record whether or not each food sample contains protein in Table 3 of the Lab Worksheet. 5. Finally, you would perform the Grease Spot Test. Again, you would label seven small test tubes, one for each food sample. Two ml of methylene chloride would be added to each tube. You would then add approximately .1g of each prepared food sample to the appropriately labeled test tube. Several drops of each solution would be added to a sheet of paper and allowed to evaporate. Based on the translucency results, record whether or not each food sample contains lipids in Table 3 of the Lab Worksheet. C. Virtual Lab Instructions Data Analysis and Synthesis Questions: 1. What are the small subunits (monomers) found in each of these types of organic compounds: protein:_____________________ ! starch: _____________________ ! lipid: ! ___ _________________, and _____________________ Table 1. Positive and Negative Controls Reagent Benedict’s Substance Tested Appearance after test Glucose Water Iodine Starch Biuret Albumin Water water Grease Spot Test Oil Water 2. In the Benedict’s test, the Benedict’s reagent tests for simple sugars, e.g. glucose. a. Name the color of the reaction when glucose in present. _________________ b. _____________ will act as a negative control because it does not contain any sugar. 3. In the Iodine test, Iodine tests for starch, a complex carbohydrate. a. The color of the tube when iodine is added to starch is ____________. b. The color of the tube indicated in part (a) above is is a ______________ (positive or negative) test result for the presence of complex carbohydrates. 4. In the Biuret test, the Biuret reagent tests for proteins. Describe the change that occurs when Biuret reagent is added to the test tube when proteins are present.