The Life Sciences Recent Progress and Application to Human Affairs The World of Biological Research Requirements for the Future (1970) / Chapter Skim
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The Language of Life
The Language of Life
Pages 36-51
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From page 36... ...
Undoubtedly, however, the crowning achievement of this era has been the spectacular growth of understanding of that process central to life itself-the chemical encoding of genetic information, the mechanism whereby it is read out to give direction to the life of the cell, and the mechanism whereby it is reproduced in the course of cell division. This area of understanding variously termed molecular biology, biochemical genetics, the chemistry of reproduction, or the biochemistry of nucleic acids and proteins-flowered when the stage had been set.
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From page 37... ...
Belief in this concept began with the observations of Garrod in 1908, who assembled then-existing information concerning six hereditary diseases of man, indicating that each was the consequence of loss of some enzymic ability. This concept was solidified with studies of a bread mold, Neurospora crassa, which ordinarily can be grown on extremely simple nutritional media and synthesizes for itself all the usual amino acids, carbohydrates, purines, pyrimidines, vitamins, etc.
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From page 40... ...
B51 A38 A3 A33 A487 A23 A46 A7 8 A5 8 A96 A446 A223 A187 A169 Genetic map l l l l (not to scale) - =r I I I I =Jja Genetic map distances W.4~.7+0~1.6~.04~.3+.4~.0014.06~.55.001~.02~.3 Amino acid in wild-type protein 1 Amino acid in m uta nt prot2 in I Position of change H2N-1-48 48 174 - 176-182 - 210 - 210 - 212 - 233-233 - 234 267-COOH In the protein , I :48+041 26~2+6~28+0+2~21~0+1-33 Glu Glu Tyr Leu Thr Gly Gly Gly Gly Gly Ser Val Met Cys Arg He Arg Glu Val Cys Asp Leu Residue distance in polypeptide chain FIGURE 5 Colinearity of the amino acid sequence of the enzyme tryptophan synthetase and the substructure of the gene that governs its synthesis.
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From page 41... ...
along a chain of 146 amino acid residues, there occurs a substitution of the amino acid valine for glutamic acid. This observation, with its profound implications for the understanding of genetic disease, reveals the nature of the simplest possible kind of mutation: A change in the structure of the genetic material at one point along the strand of genetic instruction results in substitution of one amino acid for another in the strand of amino acids.
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From page 42... ...
In all specimens of DNA, A - T and G - C, whereas there is no consistent relationship between A and G The meaning of this constancy was not apparent until combination of this information with studies of the x-ray-diffraction pattern of nucleic acids led to the now well-known depiction of DNA as two very long strands wrapped about each other in the familiar double helix, and so aligned that, on the strands, every A is opposed by a T
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From page 43... ...
The horizontal lines represent hydrogen bonds between opposing pairs, two for each AT couple, three for each GC couple.
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From page 44... ...
/ FIGURE 8 Molecular dimensions and hydrogen bonding of base pairs of DNA. (Adapted from S
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From page 45... ...
In this concept, instructions for protein synthesis must be provided by the linear sequence of bases along the DNA strand; given the fact that the chromosome of E cold consists of a single helix of about 10 million consecutive base pairs, and that any one of the four bases may lie to left or to right of any other base, there is essentially an unlimited number of statistical possibilities, only one of which is the actual structure of a specific DNA chromosome.
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From page 46... ...
In the cells of higher organisms, DNA is locked in the nucleus, whereas protein synthesis occurs in small bodies called `'ribosomes" stippled throughout the cytoplasm. It followed, therefore, that the instructions for protein synthesis in the DNA must be dispatched from the cell nucleus to the ribosomes.
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From page 47... ...
Within the cell there is a family of "amino acid-activating enzymes," and the fact that the entire apparatus actually works successfully rests on the remarkable properties of these enzymes. In absolutely specific fashion, each such enzyme esterifies one and only one of the 20 amino acids to the hydroxyl group at the 2-position of the ribose at one end of one specific form of tRNA; it is imperative that the enzyme make no error since any such error would necessarily become an error in protein synthesis.
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From page 48... ...
K Kung, "Large Oligonucleotides Isolated from Yeast Tyrosine Transfer Ribonucleic Acid after Partial Digestion with Ribonuclease T1," J
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From page 49... ...
In bacterial forms, it would appear that the first amino acid in the chain is always the same-methionine, the amino group of which bears a formyl group. Message reading, therefore, begins by utilizing formyl methionine tRNA as the first "word" and is terminated when any one of the three nonsense words shows in the message.
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From page 50... ...
If double-stranded DNA is brought to an elevated temperature, the double helix comes apart and the DNA becomes individual random flopping coils. If the temperature is then lowered very slowly, the coils find each other and the double helix is restored.
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From page 51... ...
Self-Assembly Such studies demonstrated that base pairing is the primary mechanism involved in DNA duplication, in the synthesis of RNA on DNA, and in message reading in the ribosome. But they also demonstrated a cardinal principle of the biological world, the principle of self-assembly.
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