[...]... 12/22/11 2:07 PM 12 THE EVOLUTION OF CELLS IS THERE LIFE OUT THERE? The presence of life somewhere else in the universe is not just the stuff of science fiction Astrobiology is the branch of science that studies the possibility of life elsewhere in the universe Astrobiologists also explore the chemistry of interstellar space, the habitability of planets, and evolutionary biology of Earth’s organisms... body’s billions of cells count on the energy your food provides them What follows is an exploration of some basic principles of organic chemistry and an explanation how they have contributed to the development of cells of increasing complexity CARBON, THE BACKBONE OF LIFE Cells are composed of a huge variety of complex molecules containing carbon Why carbon? The elemental structure of carbon makes... number of base pair types, the coded information they can convey is almost unlimited because there are so many of them and because of the stable helical structure in which they are bound Proteins Proteins form another of the macromolecule groups that take a variety of complex forms, but they are made up of simple modular structures that are bonded tightly together These chemical modules are amino acids The. ..10 THE EVOLUTION OF CELLS Then, in 1859, the French Academy of Science sponsored a competition for the best experiment to prove or disprove the idea of spontaneous generation Louis Pasteur, a prominent scientist of the time, set out to disprove the idea His experiment has become a classic example of what we know as the scientific method, which forms the basis of all modern science... through cycles of heat and cold At some point, the right chemicals got together under just the right conditions for life to begin 19 CBBL_EvolCells_F2_IBT.indd 19 12/22/11 2:07 PM 20 THE EVOLUTION OF CELLS Whenever we picnic under the shade of a tree on a hot summer day, we sit surrounded by organic chemistry and never give it a thought The wood of the picnic table, the corn chips we eat, the leaves providing... providing our shade, the ants crawling about, our very selves—they are all containers of organic chemicals that form the core of our existence All living things are composed of cells, and the business of a cell is chemistry Our human cells contain the same chemical compounds and undergo similar chemical processes as the cells in the corn we eat and the bacteria that live all around us The next time you... CBBL_EvolCells_F2_IBT.indd 28 12/22/11 2:08 PM The Chemistry of Life 29 of chemical energy to a site in the cell that requires it There, the electrons are unhooked, releasing (or “spending”) their stored energy The triphosphate portion of the ATP molecule consists of a chain of three phosphate groups; the bonds joining them are rich in potential energy Remember that peanut butter sandwich? The energy... millions of years, specialized cells and tissues developed to facilitate the internal exchange of gases, a process that takes place in the gills of fish and the lungs of mammals Human lungs play an essential role in the process of cellular respiration by providing the required oxygen and removing the waste carbon dioxide Respiration is a complementary process to photosynthesis, and together, they are the. .. resembling a strand of RNA At the Scripps Research Institute, molecular biologist Gerald F Joyce and colleagues CBBL_EvolCells_F2_IBT.indd 16 12/22/11 2:07 PM The Beginnings of Life 17 have produced forms of RNA molecules that can promote each other’s synthesis, as they attempt to recreate a key element of life: genetic material that can reproduce itself THE PARADOX OF THE FIRST CELL Cells of present-day... ribosomes These complexes contain both RNA and protein components Recent biochemical analysis indicates that the mechanism for protein assembly is catalyzed by the RNA portion of the complex, not protein CBBL_EvolCells_F2_IBT.indd 17 12/22/11 2:07 PM 18 THE EVOLUTION OF CELLS Thus, ribosomes within each of our cells carry this “fossil” evidence that life developed in an RNA world The other essential role of . • • 1 The Beginnings of Life 7 2 The Chemistry of Life 19 3 Prokaryotes: the Simplest Cells 30 4 Eukaryotes: the Cells of Complex Life 40 5 Cells in. PM12/22/11 2:07 PM TERRY L. SMITH CELLS THE BUILDING BLOCKS OF LIFE The Evolution of Cells CBBL_EvolCells_F2_IBT.indd 3CBBL_EvolCells_F2_IBT.indd 3 12/22/11