Welcome to my DNA Education Page
The Human Genome:
A genome is the collection of an organism's genetic material. The human genome is composed of about 30,000 genes located on the 23 pairs of chromosomes in a human cell. A single human chromosome may contain more than 250 million DNA base pairs, and it is estimated that the human genome consists of about 3 billion base pairs.
The DNA being analyzed in the Human Genome Project typically comes from small samples of blood or tissue obtained from many different people. Although the genes in each person's genome are made up of unique DNA sequences, the average variation in the genome of two different people is estimated to be much less than 1 percent. Thus the differences between human DNA samples from various sources are small in comparision to their similarities.
The Structure of DNA:
The most important component of a chromosome is the single continuous molecule of DNA. This double-stranded molecule, shaped like a twisted ladder, is composed of linked chemical compounds known as nucleotides. Each nucleotide consists of three parts: a sugar known as deoxribose, a phosphate compound, and any one of four bases-adenine, thymine, guanine, or cytosine. These parts are linked together so that the sugar and the phosphate form the two parallel sides of the DNA ladder. The bases from each side join in pairs to form the rings of the ladder-specifically, adenine always pairs with thymine, and guanine always with cytosine.
The genetic code is specified by the order of adenine, thymines, guanines, and cytosines in the DNA ladder. A particular section of the DNA ladder usually has a unique sequence of base pairs. Because a gene is merely one of these sections of the DNA ladder, it too possesses a unique sequence of base pairs, and this sequence can be used to distinguish the gene from genes and to map its location on the chromosome.
Gene Action: DNA and the Code of Life
For more than 50 years after the science of genetics was established and the patterns of inheritance through genes were clarified, the largest questions remained unanswered: How are the chromosomes and their genes copied so exactly from cell to cell, and how fo they direct the structure and behavior of living things? Two American genetics, George Wells Beadle and Edward Lawrie Tatum, provided one of the first important clues in the early 1940s.
Working with the fungi Neurospora and Penicillium, they found that genes direct the formation of emzymes through the units of which they are composed. Each unit (a polypedtide) is produced by a specific gene. This work launched studies into the chemical nature of the gene and helped to establish the field of molecular genetics.
That chromosomes were almost entirely composed of two kinds of chemical substances, proteins and nucleic acids, had long been known. Partly because of the close relationship established between genes and enzymes, which are proteins, proteins at first seemed the fundamental substance that determined heredity. In 1944, however, the Canadian bacteriologist Oswald Theodore Avery proved the deoxribonucleic acid (DNA) performed this role. He extracted DNA from one strain of bacteria and introduced it into this role. He extracted DNA from one strain.
A cell going through different stages
Count A, B, C
...1, 2, 3 !
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(This page was graded on 04/10/01)