Macromolecule Laboratory Report: Carbohydrates, Lipids, Proteins And Nucleic Acids

Introduction: Organic chemicals are chemicals that are carbon-based and are often associated with life functions. Of these organic compounds, four main categories are found in all living things to help keep cells alive and functioning properly. These categories are referred to as macromolecules and consist of carbohydrates, lipids, proteins and nucleic acids. These molecules are very large and necessary for structure, energy, communication, transport and almost every cell function.

Of the four categories, carbohydrates, lipids and proteins are responsible for all of the energy in every living organism. Each macromolecule is composed of subunits specific to the molecule. Simple carbohydrates, monosaccharides, are composed of a single carbon link with hydroxyl groups attached, which form into ring shapes when dissolved in water. They also contain a ketone carbonyl group, a carbon atom double-bonded to an oxygen atom, or an aldehyde carbonyl group, a carbon atom double bonded to an oxygen atom as well as a hydrogen atom (Jackson, 2017). Monosaccharides form glycosidic linkages to create a chain of monosaccharides, creating more complex carbohydrates like disaccharides and polysaccharides. Carbohydrates simple structure takes very little energy to break down, making them a great source of quick energy as well as a source of building materials and communication between cells.

Lipids are made up of hydrocarbon chains and oxygen. The electrons in the bonds between carbon atoms and between carbon and hydrogen atoms are relatively equal, making lipids nonpolar (Chandler,2017). Lipids can easily dissolve in other nonpolar substances, but in polar substances, like water, the electrons in the bonds between hydrogen and oxygen are not shared equally, making it unable to dissolve lipids. Lipids provide more energy per gram compared to carbohydrates and are used to store unused energy, insulate cells and in hormonal signaling and growth.

Proteins are made up of folded chains of amino acids, which consists of an amino group, an acidic carboxyl group and a R group that is specific to each amino acid. These amino acids are held together by peptide bonds, bonds formed through dehydration synthesis and held between the amino group of one amino acid and the carboxyl group of another (Reddy, 2018). In one experiment by R. D. Hotchkiss, the number of peptide bonds in crystalline lactoglobulin, the major whey protein in cow and goat milk, were estimated by reversing the dehydration reaction that occurs when amino acids join together. The protein was hydrolysed by a succession of enzymes and by boiling with hydrochloric acid to reverse the reaction, causing the amino and carboxyl groups to split. The increase in amino groups and carboxyl groups determined the amount of peptide bonds percent in crystalline lactoglobulin (Hotchkiss, 1939).

To confirm the presence of macromolecules, such as carbohydrates, lipids and protein, in substances, chemical indicators are often used. Indicators are substances that undergo a distinct chemical change when exposed to specific conditions. Benedict’s reagent is a mixture of sodium carbonate, sodium citrate and copper(II) sulfate. The copper(II) sulfate ions bind with oxygen from free aldehyde group in simple sugars, such as monosaccharides and some disaccharides, creating a copper(I) oxide precipitate that is reddish-brown in colour (Aryal, 2018). Iodine tests the presence of a complex carbohydrate, starch. When amylose, the crystallizable form of starch, is exposed to the negatively charged iodine, there is a charge transfer, which causes the electrons to become easier to excite to a higher energy level, and cause a change in colour to a dark blue (Goedecke, 2016). Grease, oil and fat have approximately the same refraction as paper, this means that when oil comes in contact with paper the oil fills in the tiny gaps within the paper, and causes light to transmit through the paper instead of the light scattering. Lipids will leave a translucent stain on paper where water has a lower index of refraction, causing the paper to remain opaque (Chandler, 2017). Biuret is a chemical compound containing copper(II) sulfate and sodium hydroxide. The copper(II) sulfate binds to peptide bonds, changing the structure and the sodium hydroxide makes the solution basic, causing a violet colour to be transmitted.

Purpose: Refer to Macromolecules Lab hand out (pg. 2).

Hypothesis: Water is a very small molecule, therefore it will contain no macromolecules. The pasta water will contain high amounts of both sugar and starch but little to no protein or fat because it is not hydrophobic, but it is a carbohydrate. Oil will have lipids in it due to its hydrophobic tendencies, but will not contain carbohydrates or proteins. 2% milk and chicken broth will contain the widest range of macromolecules, containing lipids and protein, since it came from an animal, and some simple sugars such as lactose and sugar added into the broth. Chicken broth also has some yeast in it, meaning it will also contain more complex carbohydrates. Apple juice is filled with sugar, both natural, from apples, and added, but it will not contain significant amount of protein, lipids or complex carbohydrates.

Analysis: The stain test had positive results for oil and milk and slightly positive results for the unknown substance x. The chicken broth did not contain lipids as predicted, there was no stain on the paper and it did not make the paper translucent. For the Benedict’s test, the chicken broth reacted, turning green in colour, meaning that traces of reducing sugars were found. The pasta water turned into dark yellow colour, indicating that a moderate amount of simple sugars were found. The milk and apple juice contained the most reducing sugars, causing the indicator to turn a dark orange/red colour. Although pasta is high in carbohydrates, the sampel of pasta water contained more complex carbohydrates than predicted and less simple sugars, such as the sugar with a free aldehyde, as tested in the Benedict’s indicator test. The unknown substance x also tested positive for starch, just as the pasta water did in the iodine test. The chicken broth had a semi-positive test turning a dark purplish red indicating the presence of some starch. The biuret test provided positive results for the milk, the unknown substance x and the pasta water, but did not test positive in any other solution. These results were the most shocking because the chicken broth contained no trace of protein, but the pasta water did.

The results show an accurate representation of the macromolecules in most of the samples, however, they do not accurately show the quantity of these macromolecules. Each test is qualitative, meaning that the results show if a macromolecule is present, but not a quantitative number. If the results were quantitative, you could see the exact difference in macromolecules and rank the solutions, but since they are not, a substance with trace amounts of a macromolecule like protein could have the same reaction as a substance that is mostly protein. Also, some of the substances tested, such as the chicken broth, could have been too diluted, contaminating the results by making the concentration so low that the tests did not detect the trace amounts of macromolecules. This would make results much less accurate.

The independent variables in the lab were the different tests for the macromolecules because they were controlled and changed throughout the experiment to test all of the effects on the substances chosen for the lab. The dependent variables were the substances because the substances were being tested for macromolecules and the results were dependent on the test that it was put through. The hardest test was Benedict’s test because the samples had to be placed in a warm water bath for the reaction to occur. This caused much more room for error such as putting in the Benedict’s reagent in the samples too soon, not heating the water enough or too much and not leaving the samples in the bath long enough to react. There could have also been contaminants on the spot plates, in test tubes or in pipettes causing a reaction to occur that should not have. A negative control is a sample that is expected to get no reaction. In this lab water was used because it is too small to contain macromolecules and therefore should not react to any of the tests. Negative controls are used to compare to other samples to check if there were any reactions.

Macromolecules are the basic essentials that make up the human body. They provide cells with energy to help keep them alive and performing all of their functions properly. There is a great advantage to knowing the exact chemical makeup of food because it is what is fueling our entire body. Humans need a balance of all macromolecules and knowing which foods have which molecules can help that out greatly. It can help in planning for meals to ensure all macromolecules are in a person's diet. It can also help more specific health concerns. For example, if someone wanted to gain muscle and knew they needed more protein in their diet, knowing what macromolecules are in what foods can help them pick which foods they needed to start eating more of. Also, the structure of the molecules in food are important because they give it their characteristics. For example, monosaccharide are easier to break down than polysaccharides, meaning polysaccharides release energy for a longer period of time than monosaccharides. This is why it is better for athletes to eat complex carbohydrates before working out. Saturated fats have all single bonded carbons causing them to stay in a straight chain. Unsaturated fats have at least one double carbon bond giving it a bend in its chain. This is important to know because since saturated fats are all straight chains, they can stack together very compactly and cause blockage. Since unsaturated fats have a kink, they can not stack together nicely like saturated fats and therefore cause less risk of clogged or blocked arteries and other health problems.