The chemistry of life on earth is carbon and water chemistry. Water is the most abundant compound in living cells and makes up as much as 90 percent of the weight of most plant tissues.
Many of the molecules that are part of larger macro molecules in cells are linked together chemically by dehydration synthesis, or the loss of water. These macromolecules are broken up into their component units by the addition of a water molecule between the units, a process known as hydrolysis. The chemical properties of water make it an ideal solvent and buffer for the chemistry that occurs inside cells.
Because the electrons of the covalent bonds within the water molecule are more often orbiting the oxygen atom, the oxygen atom gains a slightly negative charge. The hydrogen atoms are slightly positive. This separation of charge across the water molecule is said to make it polar. Because of its polar nature, water is able to dissolve, or ionize, a variety of molecules. This gives water its buffering capacity.
Water molecules are attracted to one another because of this polarity. This weak attraction, which occurs in the form of hydrogen bonds, has great chemical consequences when many molecules of water are involved. Hydrogen bonding allows water to have surface tension. The capillary action that helps water travel up plant tissues from the roots is a direct consequence of the polarity of the water molecule. Water is also able to absorb heat without vaporizing (changing from a liquid to a gas state) quickly. Therefore, physiological temperatures can be maintained as water molecules absorb the heat from metabolic reactions.
Water, ions, salts, and gases all are types of inorganic molecules that are essential to cellular function. Inorganic molecules are chemical molecules that do not contain carbon. The remainder of the molecules within cells are built around the unique properties of the carbon atom and are called organic molecules.
Organic Macromolecules
There are four major classes of organic molecules in cells: carbohydrates, lipids, nucleic acids, and proteins.
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Carbohydrates
Carbohydrates are molecules that consist of primarily carbon, hydrogen, and oxygen atoms.
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Lipids
Lipids are diverse group of unrelated molecules which includes fats, oils, steroids and sterols, waxes, and other water-insoluble molecules.
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Nucleic Acids
The information that directs all cellular activity is contained within the chemical structure of the nucleic acids.
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Proteins
Protein molecules are large, complex molecules with a huge variety of structures and functions within cells.
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