DNA and RNA
Structure and Functions (Magill’s Medical Guide, Sixth Edition)
Each human being is a biologically unique individual. That uniqueness has its basis in one’s cellular makeup. Appearance derives from the arrangement of cells during fetal development, size depends on the cells’ ability to grow and divide, and the function of organs depends on the biochemical function of the individual cells that constitute each organ. The functions of cells depend on the types and amounts of the different proteins that they synthesize. The substance that holds the information that determines the structure of proteins, when they should be produced, and in what amounts is deoxyribonucleic acid (DNA).
DNA is the molecule of heredity, and as a child receives half of his or her DNA from each biological parent, each individual is the product of a mixture of information. Therefore, while children resemble their parents, they are unique. Each cell in an individual’s body (except for the sex cells) has a complete set of genetic information contained in the chromosomes of the cell’s nucleus. Human cells have forty-six chromosomes (twenty-three pairs). Each chromosome is a single piece of DNA associated with many types of proteins. The major function of DNA is to store, in a stable manner, the information that is the “blueprint” for all physiological aspects of an individual. Stability is one of the key attributes of DNA. An information storage molecule is of little use if it can be altered or...
(The entire section is 1465 words.)
Disorders and Diseases (Magill’s Medical Guide, Sixth Edition)
When the normal structure of DNA is altered (a process called a mutation), the number of proteins produced and/or the functions of proteins may be affected. At one extreme, a mutation may cause no problem at all to the person involved. At the other extreme, it may cause devastating damage to the person and result in genetic disease or cancer.
Mutations are changes in the normal sequence of bases in the DNA that carry the information to build a protein or that regulate the amount of protein to be produced. There are different types of mutations, such as the alteration of one base into another, the deletion of one or many bases, or the insertion of bases that were not in the sequence previously. Mutations can have many different causes, such as ultraviolet rays, X rays, mutagenic chemicals, invading viruses, or even heat. Sometimes mutations are caused by mistakes made during the process of DNA replication or cell division. Cells have several systems that constantly repair mutations, but occasionally some of these alterations slip by and become permanent.
Mutations may affect protein structure in several ways. The protein may be too short or too long, with amino acids missing or new ones added. It might have new amino acids substituting for the correct ones. Sometimes as small a change as one amino acid can have noticeable effects. In any of these cases, changes in the amino acid sequence of a protein may...
(The entire section is 1100 words.)
Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
Genetics is a young science whose starting point is traditionally considered to be 1866, the year in which Gregor Mendel published his work on hereditary patterns in pea plants. While he knew nothing of DNA or its structure, Mendel showed mathematically that discrete units of inheritance, which are now called genes, existed as pairs in an organism and that different combinations of these units determined that organism’s characteristics. Unfortunately, Mendel’s work was ahead of its time and thus ignored until rediscovered by several researchers simultaneously in 1900.
DNA itself was discovered in 1869 by Friedrich Miescher, who extracted it from cell nuclei but did not realize its importance as the carrier of hereditary information. Chromosomes were first seen in the 1870’s as threadlike structures in the nucleus, and because of the precise way they are replicated and equally parceled out to newly divided cells, August Weismann and Theodor Boveri, in the 1880’s, postulated that chromosomes were the carriers of inheritance.
In 1900, Hugo de Vries, Karl Correns, and Erich Tschermak von Seysenegg—all plant biologists who were working on patterns of inheritance—independently rediscovered Mendel’s work. De Vries had in the meantime discovered mutation around 1890 as a source of hereditary variation, but he did not postulate a mechanism. Mendel’s theories and the then-current knowledge of...
(The entire section is 634 words.)
For Further Information: (Magill’s Medical Guide, Sixth Edition)
Campbell, Neil A., et al. Biology: Concepts and Connections. 6th ed. San Francisco: Pearson/Benjamin Cummings, 2008. This classic introductory textbook provides an excellent discussion of essential biological structures and mechanisms. Its extensive and detailed illustrations help to make even difficult concepts accessible to the nonspecialist. Of particular interest are the chapters constituting the unit titled “The Gene.”
Drlica, Karl. Understanding DNA and Gene Cloning: A Guide for the Curious. 4th ed. Hoboken, N.J.: Wiley, 2004. This book for the uninitiated explains the basic principles of genetic mechanisms without requiring knowledge of chemistry. The first third is especially good on the fundamentals, but the remainder may be too deep for some readers.
Frank-Kamenetskii, Maxim D. Unraveling DNA: The Most Important Molecule of Life. Translated by Lev Liapin. Rev. ed. Reading, Mass.: Addison-Wesley, 1997. This very readable book provides an excellent history of the discovery of DNA. Also describes the nature of DNA and discusses genetic engineering and the ethical questions that surround its use.
Glick, Bernard, Jack J. Pasternak, and Cheryl L. Patten. Molecular Biotechnology: Principles and Applications of Recombinant DNA. 4th ed. Washington, D.C.: ASM Press, 2010. Explores the scientific principles of recombinant DNA technology and its wide-ranging use in...
(The entire section is 547 words.)