Biology - Biological molecules (Carbohydrates, Lipids, Proteins, and DNA tests)

Biological molecules are composed primarily of Carbon ($C$), Hydrogen ($H$), and Oxygen ($O$). Proteins also contain Nitrogen ($N$) and sometimes Sulfur ($S$). Nucleic acids like DNA contain Phosphorus ($P$).

Carbohydrates are used for energy. Monosaccharides like glucose ($C_6H_{12}O_6$) are simple sugars. Polysaccharides include starch (energy storage in plants), glycogen (energy storage in animals), and cellulose (cell wall structure).

Lipids (fats and oils) are made from one molecule of glycerol and three molecules of fatty acids. they are used for long-term energy storage, insulation, and cell membranes.

Proteins are polymers made of long chains of amino acids. The sequence of amino acids determines the $3D$ shape and specific function of the protein, such as enzymes, antibodies, or hemoglobin.

DNA (Deoxyribonucleic acid) is a double helix made of two strands of nucleotides. The strands are held together by complementary base pairs: Adenine ($A$) pairs with Thymine ($T$), and Cytosine ($C$) pairs with Guanine ($G$).

Food Test for Starch: Add Iodine solution. A positive result is a color change from orange-brown to blue-black.

Food Test for Reducing Sugars: Add Benedict's reagent and heat in a water bath at $80^{\circ}C$. A positive result changes from blue to green, yellow, orange, or brick-red (depending on concentration).

Food Test for Proteins: Add Biuret reagent (Sodium Hydroxide and Copper (II) Sulfate). A positive result is a color change from blue to violet/purple.

Food Test for Lipids: Perform the Ethanol emulsion test. Dissolve the sample in Ethanol, then add to water. A positive result is the formation of a cloudy white emulsion.