The discovery of regulator genes--genes that control the timing and output of structural genes

Date: 2015-10-07; view: 415.

Watson and Crick determine that deoxyribonucleic acid (DNA) is a double-strand helix of nucleotides. Each nucleotide consists of a deoxyribose sugar molecule to which is attached a phosphate group and one of four nitrogenous bases: two purines (adenine and guanine) and two pyrimidines (cytosine and thymine). The nucleotides are joined together by covalent bonds between the phosphate of one nucleotide and the sugar of the next, forming a phosphate-sugar backbone from which the nitrogenous bases protrude. The two strands are linked by selective hydrogen bonds: the purine adenine bonds only with the pyrimidine thymine, and the purine cytosine only with the pyrimidine guanine.

Erwin Chargaff shows that the four nucleotides are not present in nucleic acids in stable proportions, and that the nucleotide composition differs according to its biological source.

Beginning in the 1950s, Chargaff became increasingly outspoken about the failure of the field of molecular biology, claiming that molecular biology was "running riot and doing things that can never be justified".[citation needed] He believed that human knowledge will always be limited in relation to the complexity of the natural world, and that it is simply dangerous when humans believe that the world is a machine, even assuming that humans can have full knowledge of its workings. He also believed that in a world that functions as a complex system of interdependency and interconnectedness, genetic engineering of life will inevitably have unforeseen consequences. Chargaff warned that "the technology of genetic engineering poses a greater threat to the world than the advent of nuclear technology. An irreversible attack on the biosphere is something so unheard of, so unthinkable to previous generations, that I only wish that mine had not been guilty of it".

(1952)

2.1 Alfred Hershey and Martha Chase show that on infection of the host bacterium by a virus, at least 80% of the viral DNA enters the cell and at least 80% of the viral protein remains outside.

The Hershey–Chase experiments were a series of experiments conducted in 1952 by Alfred Hershey and Martha Chase that helped to confirm that DNA was the genetic material. While DNA had been known to biologists since 1869, a few scientists still assumed at the time that proteins carried the information for inheritance. In their experiments, Hershey and Chase showed that when bacteriophages, which are composed of DNA and protein, infect bacteria, their DNA enters the host bacterial cell, but most of their protein does not. Although the results were not conclusive, and Hershey and Chase were cautious in their interpretation, previous, contemporaneous and subsequent discoveries all served to prove that DNA is the hereditary material. Knowledge of DNA gained from these discoveries has applications in forensics, crime investigation and genealogy.[clarification needed]

(1953)

DNA replication is possible through the complementary nature of the two strands. The chemical complexity of the molecule is thought to be sufficient to store the requisite information. The precise manner in which the information in the DNA is activated to build an organism is still very poorly understood; what is firmly demonstrated is that so-called structural genes manufacture the proteins for living tissues.

In the late nineteenth century, a German biochemist found the nucleic acids, long-chain polymers of nucleotides, were made up of sugar, phosphoric acid, and several nitrogen-containing bases. Later it was found that the sugar in nucleic acid can be ribose or deoxyribose, giving two forms: RNA and DNA. In 1943, American Oswald Avery proved that DNA carries genetic information. He even suggested DNA might actually be the gene. Most people at the time thought the gene would be protein, not nucleic acid, but by the late 1940s, DNA was largely accepted as the genetic molecule. Scientists still needed to figure out this molecule's structure to be sure, and to understand how it worked. In 1948, Linus Pauling discovered that many proteins take the shape of an alpha helix, spiraled like a spring coil. In 1950, biochemist Erwin Chargaff found that the arrangement of nitrogen bases in DNA varied widely, but the amount of certain bases always occurred in a one-to-one ratio. These discoveries were an important foundation for the later description of DNA. In the early 1950s, the race to discover DNA was on. At Cambridge University, graduate student Francis Crick and research fellow James Watson (b. 1928) had become interested, impressed especially by Pauling's work. Meanwhile at King's College in London, Maurice Wilkins and Rosalind Franklin were also studying DNA. The Cambridge team's approach was to make physical models to narrow down the possibilities and eventually create an accurate picture of the molecule. The King's team took an experimental approach, looking particularly at x-ray diffraction images of DNA.

(Early 1970s)

2.3 Comparisons between chimpanzee and human genomes finds that they diverge by only 1.6%--less than most sibling species, which barely differ in morphology, and far less than that between any pair of congeneric species.

The theoretical implications are unclear; morphological and behavioral differences between the two species appeared to be unaccounted for by the genetic material (cf. Cherry et al, 1978; for an update, see Gibbons 1998).

(Early 1970s)

Since a regulator gene may control thousands of structural genes, and indeed other regulator genes, the logical inference is that human and chimpanzee genomes are being switched on and off in quite different ways (King & Wilson 1975)

Leland Hartwell was the pioneer of studying cell cycle using genetic methods. He made use of the yeast Saccharomyces cerevisiae as the subject of his experiments. In the year 1970, he tried to isolate individual gene that he thought were vital in the control of cell cycle. Successfully, he was able to isolate cells wherein the cell cycle regulator genes were dysfunctional. By the use of this same method, he was able to isolate more than a hundred genes that were directly involved in the control of cell cycle. He called these genes CDC gene which stands for cell division cycle genes. Among the hundreds of CDC genes that he was able to isolate, he noted CDC28 gene for it was observed to control the first step of the cell cycle, progression from the G1 phase. For this function he named the gene, “start.” He also introduced the concept of “checkpoints” wherein the cell cycle stops to check whether the DNA was perfectly duplicated.

(1980s)