From Molecules To Celllike Structures

Sidney Fox (1912-1998) and others have done extensive research on the physical structures that may have given rise to the first cells. These cell-like structures, such as the ones shown in Figure 14-7, form spontaneously in the laboratory from solutions of simple organic chemicals. The structures include microspheres, which are spherical in shape and are composed of many protein molecules that are organized as a membrane, and coacervates (coh-AS-uhr-VAYTS), which are collections of droplets that are composed of molecules of different types, including lipids, amino acids and sugars.

For many years, it had been assumed that all cell structures and the chemical reactions of life required enzymes that were specified by the genetic information of the cell. Both coacervates and microspheres, however, can form spontaneously under certain conditions. For example, the polymers that form microspheres can arise when solutions of simple organic chemicals are dripped onto the surface of hot clay. The heat vaporizes the water, encouraging polymerization. Coacervates and microspheres have a number of celllike properties, including the ability to take up certain substances from their surroundings. Coacervates can grow, and microspheres can bud to form smaller microspheres. These properties of coacer-vates and microspheres show that some important aspects of cellular life can arise without direction from genes. Thus, these studies suggest that the gap between the nonliving chemical compounds and cellular life may not be quite as wide as previously thought.

However, microspheres and coacervates do not have all of the properties of life. These cell-like structures do not have hereditary characteristics. Thus, these structures cannot respond to natural selection. Scientists are still investigating hypotheses about how living cells may have formed from simpler ingredients.

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