Biochemistry Lab Background

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     Biochemistry is the study of the chemical processes of organisms. Many biochemical processes involve large organic compounds: carbohydrates, proteins, and lipids. In this activity you will perform a variety of tests to identify these organic compounds.

Carbohydrates

     Carbohydrates are organic compounds that contain atoms of carbon, hydrogen, and oxygen in the general formula (CH2O)n. On the basis of the number of monomers they contain, carbohydrates are organized into three major categories:

• • monosaccharides; simple sugars such as glucose and fructose 

  •  disaccharides; two chemically bonded monosaccharides such as sucrose, maltose, and lactose

  • polysaccharides; made of many monosacchartides

    • structural support (cellulose)

    • energy storage  (starch)

     The chemical test for a monosaccharide and some disaccharides involves a chemical called Benedict's solution. The benedicts reaction will occur with a monosaccharide turning the blue solution orange. 

     A starch complex carbohydrate can be tested using an iodine-potassium iodide IKI solution. The interaction of the iodide solution and the starch molecule causes a reaction and makes a very dark solution. 

Proteins

     Proteins are large polymers formed from monomers called amino acids. Amino acids contain atoms of hydrogen, oxygen, carbon, and nitrogen in the general chemical formula NH2-RCH-COOH, where -R represents a carbon chain or ring that may carry -OH, -H, -S, -P, and so on. The properties of an amino acid depend on the structure of its -R group.  

     The proteins and amino acids contained in foods are a source of prefabricated amino groups. Although some amino acids can be synthesized in the human body, there are "essential" amino acids that must be supplied in prefabricated form from the diet. The nine amino acids considered essential are histidine,

isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. The absence of any of these halts synthesis of certain proteins, resulting in disease and, in prolonged cases, death.

    Biuret reagent is used to test for peptides containing three or more amino acids. It will change color from blue to purple in the presence of proteins.

Lipids

     Lipids are a diverse group of organic compounds classified together because they are hydrophobic (insoluble in water). Lipids often contain long, nonpolar

hydrocarbon chains. As the name suggests, hydrocarbons are made carbon and hydrogen atoms. If all carbon atoms are joined by single- covalent bonds, the hydrocarbon is saturated. If some carbon atoms are joined by double-covalent bonds, the hydrocarbon is unsaturated. Subcategories of lipids include triglycerides, phospholipids, and steroids.

     In this lab, we will be focusing on triglycerides. Triglycerides are made of a molecule of glycerol and three fatty acids. The fatty acids can be saturated or unsaturated. 

     Saturated fatty acid chains are straight and are more dense. They are solid at room temperature.  If the fatty acids are mainly saturated, containing as much hydrogen as is possible, the triglyceride will be a fat. Typically, fats are solid at room temperature.

     If the fatty acids are mainly unsaturated (containing less than the maximum amount of hydrogen), the triglyceride will be an oil. he double bonds of unsaturated fatty acids cause the chain to bend, taking up more space.Typically, oils are liquid at room temperature. Animals usually store lipids as saturated fats, while plants tend to store lipids as unsaturated oils. 

     Lipids can be indicated by a simple laboratory test using Sudan III Fat Stain. The dye is insoluble in water, but will be concentrated in the oil layer and will have a red-scarlet hue. This is a physical mixture and not a reaction with lipids. 

Triglyceride Synthesis

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