CHAPTER ONE: CHEMICAL FOUNDATIONS OF LIFE This chapter introduces molecular biology by talking about the basics of biochemistry as it applies to life and living things. All of human life is based on water, which is a polar molecule that acts as a solvent for many biological molecules in living things. The bonds that make up biochemical molecules are also important in the discussion of molecular biology. The types of molecules that make up living organisms is also covered as are the different biochemical reactions that take place inside and outside the cell. Water Biochemistry Water is the common solvent found in all forms of life. Humans are about 70 percent water, while many marine organisms, such as jellyfish, are as much as 95 percent water. The oxygen that humans and animals breathe ultimately come from the water—turned into oxygen by the activities of photosynthetic plants. Plants and other organisms that are photosynthetic will take water and sunlight to make food, with oxygen as a waste product. Water is extremely abundant with about 350 million cubic miles of water on earth. About 97 percent of this is in the oceans of the earth, covering two-thirds of the planet’s surface. About 90 percent of all of the fresh water on earth is frozen in the poles and in glaciers. Only 1 percent of the water on the planet is drinkable, mostly found in underground aquifers. While water is a simple molecule, its characteristics are extremely important in molecular biology. Its chemical structure, H2O, means that it contains two atoms of hydrogen and one atom of oxygen, bonded in a V shape. Figure 1 shows what the molecular structure of water is:
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