The molecular level of life. Chemical composition of the cell

At the molecular level, the organic compounds of the cell – proteins, nucleic acids, carbohydrates and lipids – are studied, together with their structure and functions. Macromolecules are built by joining small units, monomers: the monomer of a protein is an amino acid, of a nucleic acid a nucleotide, of starch glucose. Such large and varied molecules exist because the carbon atom can form strong bonds and long chains with other atoms. At this level, hereditary information is stored and copied, solar energy is converted into the energy of chemical bonds in photosynthesis, and the energy of breakdown is stored in ATP, the universal energy carrier. The processes are arranged in an orderly way: protein synthesis takes place in ribosomes, glycolysis in the cytoplasm, respiration in mitochondria and photosynthesis in chloroplasts. A molecule isolated from a cell keeps only its chemical and physical properties; its vital role appears in the whole cell system.