Chemistry of the Living Cell

Chemistry of the Living Cell

Much of a cell's activities involve the arranging and rearranging and bonding of macromolecules.  By encoding and directing the production of proteins, DNA both directly and indirectly coordinates and directs these activities.

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The living cell is a symphony of thousands of chemical reactions all miraculously timed and coordinated to perform all the functions necessary for life. Amazingly, this symphony has only a few major players. Only six elements carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur (remember CHNOPS) make up about 98% of the mass of all living organisms. 

Much of a cell's activities involve the arranging and rearranging and bonding of macromolecules.  By encoding and directing the production of proteins, DNA both directly and indirectly coordinates and directs these activities.

The living cell is a symphony of thousands of chemical reactions all miraculously timed and coordinated to perform all the functions necessary for life. Amazingly, this symphony has only a few major players. Only six elements carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur (remember CHNOPS) make up about 98% of the mass of all living organisms. 

Carbon is a unique element with the remarkable ability to form strong, stable chemical bonds with other atoms. Each carbon atom can form four bonds with other atoms. (Sometimes, two atoms will form more than one bond between themselves making a double bond or even a triple bond). This bonding ability allows carbon atoms to form chains of almost unlimited length. These chains can be closed on themselves to form rings or may branch wildly. This gives virtually infinite variety to the kinds of molecules that carbon can form. Carbon containing compounds are called organic compounds.

Figure 1 shows just a few examples of the many ways carbon chains can be arranged to form the skeleton for different molecules.

Structural formulae showing carbon bonding
Figure 1

Atoms of hydrogen and oxygen and less frequently nitrogen, sulfur, or phosphorous bond to the carbon skeleton in a variety of ways to form small but complex molecules.

The four major types of macromolecules found in living cells—carbohydrates, lipids, proteins, and nucleic acids--are made of these smaller, repeating subunits called monomers. The monomers within one molecule are not always identical but they always have similar chemical structures. Monomers are joined together by a series of chemical reactions in a process called polymerization to form large, complex molecules called polymers. Poly means many. Another prefix you will run into later in your study of DNA testing is oligo. An oligomer is also a molecular made of repeating subunits but fewer in number than a polymer. For example, an oligonucleotide is a short change of nucleotides whereas a polynucleotide may have many, many nucleotide subunits. You may also run across the terms dimers, trimers, and tetramers—oligomers composed of two, three, and four monomers respectively.

Table of four kinds of macromolecules

The chemical diversity that polymerization allows living things is similar to the diversity that our alphabet allows our language. Although there are only 26 letters in our English  alphabet, our ability to join them together to form words gives us an almost infinite variety of possible words. Similarly, the monomer units of macromolecules can be arranged with an almost endless potential for variety.

The functions of macromolecules are directly related to their shapes and to the chemical properties of their monomers. The way the monomers are arranged in the macromolecule determines its shape and its function in the same way that the arrangement of the letters in a word determine its sound and meaning.

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Where Can I Go From Here?

©️2002 - 2017 Context.info

Contexo.info is a not for profit, educational website.