Biochemistry - The History and Development of Cells

Biochemistry - the history and development of cells
​Despite the enormous diversity of living systems, all creatures on Earth exhibit remarkable molecular uniformity, proving that they have a common origin and have undergone evolution. At least 3.8 billion years ago, life initially appeared, yet it is still unknown how the first cell and life itself arose. Experiments have demonstrated that in the circumstances believed to exist in the early Earth's atmosphere, the so-called prebiotic epoch, simple organic molecules can synthesise and spontaneously polymerize into macromolecules. The ability of the macromolecules to self-replicate, as seen with modern nucleic acids, and to catalyse other reactions, as seen with ribonucleic acid (RNA), was the next crucial step (Section G1). The first cell is thought to have developed as a result of the self-replicating RNA being enclosed in a membrane made of phospholipids (Section E1), thereby insulating the cell's interior from its surroundings. Thus, the enclosed macromolecules would have continued to function as a single unit, able to self-replicate and undergo additional development to give rise to the variety of life forms observed on Earth today. An evolutionary path from a common ancestral cell to the cells and animals of today can be inferred by examination of the deoxyribonucleic acid (DNA) sequences of organisms. Bacteria, archaea, and eukaryotes are the three main divisions or domains of the living world. The bacteria, which include cyanobacteria, Escherichia coli (E. coli), and the Bacillus species as well as living in or on larger organisms, are the prokaryotes most frequently found in soil, water, and other environments (photosynthetic blue-green algae). The sulphur bacteria and the methanogens are among the uncommon archaea, although some can also be found in less harsh conditions like salt brines, hot acid springs, and the depths of the ocean.