Biology - Biological Molecules

Biological molecules are composed primarily of the elements 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 as energy sources and structural units. Monosaccharides like glucose ($C_6H_{12}O_6$) are single sugar units. Disaccharides like sucrose are two units, and polysaccharides like starch, glycogen, and cellulose are long chains of glucose.

Lipids (fats and oils) are molecules used for long-term energy storage and insulation. They are constructed from one molecule of glycerol and three molecules of fatty acids.

Proteins are polymers made of long chains of amino acids. The specific sequence of amino acids determines the 3D shape of the protein, which is vital for its function as an enzyme, antibody, or hormone.

DNA (Deoxyribonucleic acid) is the molecule of heredity. It consists of two strands twisted into a double helix, held together by complementary base pairs: Adenine ($A$) with Thymine ($T$), and Cytosine ($C$) with Guanine ($G$).

Water ($H_2O$) acts as a universal solvent in biological systems, facilitating chemical reactions and the transport of dissolved substances within the blood and xylem.

Food tests: Benedict's solution (blue to brick-red for reducing sugars), Iodine solution (yellow-brown to blue-black for starch), Biuret test (blue to violet for proteins), and Ethanol emulsion test (milky white emulsion for fats).