Chemicals of life

We absorb molecules from the food we eat and either use them for their energy content or else incorporate them into the various structures that give our bodies both form and function. No molecule in a living organism is a permanent resident, however. Rather, there is perpetual change as molecules ingested in the latest batch of food are transformed to replace older molecules in the organism. Within 7 years, for example, most of the molecules in a human body have been replaced by new ones—the body you have today is not the one you had 7 years ago  

What then is an individual If not the molecules themselves, then how about the patterns in which they are assembled A glance at a set of identical twins tells you the answer to this second question is no. The molecular patterns in any organism are determined by the organism s genetic code, and identical twins have identical genetic codes. Each member in a set of identical twins has its own unique personality, however, despite the fact that the two persons have identical molecular patterns. 

Interestingly, the genetic code you have today is the same as the one you had in your yesteryears, but you are now made of a different set of molecules—not unlike two identical twins. Aside from memories, perhaps you are as different from your past self as two identical twins are from each other. Perhaps an individual s identity is continually reestablished each and every moment. 

Although this chapter cannot promise any insights into the intriguing questions of existence, it will give you a basic understanding of biomolecules—the molecules that make up living organisms—arid the remarkable roles they play in your body. 

Every cell has a plasma membrane. More than just a boundary, the plasma membrane allows molecules to pass into and out of the cell and provides sites where important chemical reactions occur. In animal cells, the plasma membrane is the outermost part of the cell, but the plasma membranes of plant cells are bounded by a rigid cell wall that protects the cells and gives them structure. 

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Oxygen reacts with hydrogen in a ratio of one to two, as does sulfur, selenium, and tellurium. It is this chemical reactivity, the ability of elements to join chemically into compounds, that is responsible for transformation of the elements of the cosmos into the materials of Earth and ultimately the materials of life. Although we have to put off our detailed discussion of the complex molecules of life until we have a firmer foundation, we already have enough information to discuss two of the most important chemicals of life and decidedly life s necessary precursors salt and water. The first life formed in the salty oceans, as evidenced by the salty solutions of our cells, and is always present in the salty character of our bodies. 

The chapter concludes with a discussion of the nucleic acids, which are the genetic material of living systems and which direct the biosynthesis of proteins. These two types of biopolymers, nucleic acids and proteins, are the organic chemicals of life. 

Professor Asimov has to his credit an impressive list of over sixty books in all. Among them are The Intelligent Man s Guide to Science, The Chemicals of Life, Life and Energy, The Genetic Code, and Inside the Atom. 

BIOCHEMISTRY AND HUMAN METABOLISM THE CHEMICALS OF LIFE CHEMISTRY AND HUMAN HEALTH INSIDE THE ATOM... 

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