Biol Report 2
Alibrahim
Exp1sp2019-2.pptxChemical Aspect
Organic Molecules
Organic compounds contain carbon atoms linked together to form chains or rings. Four classes of organic compounds—carbohydrates, lipids, proteins and nucleic acids—are found in large amounts in living organisms. The chemical properties of the different classes depend on the presence of specific functional groups. In general, the larger molecules in each class are formed by joining one or more building block molecules together in a dehydration synthesis reaction during which a molecule of water is formed for each building block added. Large molecules are broken down into the smaller building block molecules by a reverse reaction called hydrolysis during which water is added. In this exercise you will learn about the structure and properties of carbohydrates, lipids and proteins and how to test for the presence of these organic molecules.
I. Carbohydrates
Carbohydrates are the main energy-storage molecules in most organisms. The building blocks of carbohydrates are small molecules called sugars, composed of carbon, hydrogen and oxygen. Carbohydrates are classified according to the number of sugar molecules they contain. Monosaccharides, such as glucose, fructose, ribose, and galactose, contain only one sugar molecule. Disaccharides, such as sucrose, maltose and lactose, contain two sugar molecules linked together. Polysaccharides, such as starch, glycogen, cellulose and chitin, contain many sugar molecules linked together.
A. Tests for Carbohydrates:
Benedict ’s test for reducing sugars: Benedict’s reagent (a blue colored solution containing copper ions) is used to test for the presence of reducing sugars. When a solution containing Benedict’s reagent and a reducing sugar is heated, the copper (II) ions in the Benedict’s reagent are reduced to copper (I) ions and the solution changes from blue to a brick-red precipitate (solid) at the bottom.
2. Lugol’s( iodine) test for starch: Iodine is a yellow brown color solution that react with starch giving blue-black color reaction.
II. Proteins
Proteins are complex, specialized molecules composed of carbon, hydrogen, oxygen, and nitrogen. Many proteins also contain sulfur. The building blocks of proteins are the amino acids. There are twenty different amino acids commonly found in proteins. All of these amino acids have a similar structure.
Biuret Test for Proteins: Biuret reagent is a light blue solution which turns purple when mixed with a solution containing protein. A purple color reaction is formed when copper ions in the biuret reagent react with the peptide bonds of the polypeptide chains of the proteins.
III. Lipids
Lipids are organic molecules that are insoluble in water and other polar solvents. Lipids are readily soluble in nonpolar solvents, such as chloroform, benzene, and ether. Lipids include fats and oils (important as energy storage compounds), phospholipids and glycolipids (part of the structure of cell membranes), waxes (protective surface coatings on many plants and animals), and steroids (found in some cell membranes and many hormones).
At home (any brown paper) Starbucks brown paper bag for example can be used or any brown bag
Noura Basha (NB) -
Procedure:
Add up to 1 ml Benedict’s reagent into test tube Glucose solution, and Water (negative control)? Why?
Shake gently to mix them, and then put them in hot water bath for 10 min (explain this step)?
Observe color changes, and record the results in the table.
Add 1 ml of iodine in starch solution and water test tube.
Observe color changes, and record the results in the table.
Add up to 1 ml of Biurette reagent into egg white solution , and Water.
Shake gently, Observe color changes, and record the results in the table.
Use two pieces of brown paper bag add one drop of vegetable oil into one , the add one drop of water into anther piece, observe the changes after 10 min and after 30 min. ( at home)
Result
| Tested items | Organic compound tested | Substance Tested | Result |
| Iodine | Starch | Starch ------------- Water | |
| Benedict’s | Reducing Sugar | Glucose ------------- Water | |
| Paper spot | Lipids | Oil ------------- Water | |
| Biuret | Protein | Egg white ------------- Water |
Write the experiment above in a scientific lab report.
Your Purpose Discussed in class:----------------------------------------------------------------------------------------------------------------------------------------------
(Typed)
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