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The Gene: An Intimate History is a book written by Siddhartha Mukherjee, an Indian-born American physician and oncologist. It was published on 17 May
Table of contents

For full treatment, see heredity. Genes are composed of deoxyribonucleic acid DNA , except in some viruses , which have genes consisting of a closely related compound called ribonucleic acid RNA.

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A DNA molecule is composed of two chains of nucleotides that wind about each other to resemble a twisted ladder. The sides of the ladder are made up of sugars and phosphates, and the rungs are formed by bonded pairs of nitrogenous bases. These bases are adenine A , guanine G , cytosine C , and thymine T.

An A on one chain bonds to a T on the other thus forming an A—T ladder rung ; similarly, a C on one chain bonds to a G on the other. If the bonds between the bases are broken, the two chains unwind, and free nucleotides within the cell attach themselves to the exposed bases of the now-separated chains. The free nucleotides line up along each chain according to the base-pairing rule—A bonds to T, C bonds to G. This process results in the creation of two identical DNA molecules from one original and is the method by which hereditary information is passed from one generation of cells to the next.

The sequence of bases along a strand of DNA determines the genetic code. When the product of a particular gene is needed, the portion of the DNA molecule that contains that gene will split. Through the process of transcription, a strand of RNA with bases complementary to those of the gene is created from the free nucleotides in the cell. This single chain of RNA, called messenger RNA mRNA , then passes to the organelles called ribosomes , where the process of translation , or protein synthesis, takes place. Each set of three nucleotides codes for one amino acid.

The series of amino acids built according to the sequence of nucleotides forms a polypeptide chain ; all proteins are made from one or more linked polypeptide chains. Experiments conducted in the s indicated one gene being responsible for the assembly of one enzyme , or one polypeptide chain. This is known as the one gene—one enzyme hypothesis. However, since this discovery, it has been realized that not all genes encode an enzyme and that some enzymes are made up of several short polypeptides encoded by two or more genes. Experiments have shown that many of the genes within the cells of organisms are inactive much or even all of the time.

Thus, at any time, in both eukaryotes and prokaryotes, it seems that a gene can be switched on or off. The regulation of genes between eukaryotes and prokaryotes differs in important ways. The process by which genes are activated and deactivated in bacteria is well characterized. Bacteria have three types of genes: structural, operator, and regulator. Structural genes code for the synthesis of specific polypeptides.

Operator genes contain the code necessary to begin the process of transcribing the DNA message of one or more structural genes into mRNA. Thus, structural genes are linked to an operator gene in a functional unit called an operon. Ultimately, the activity of the operon is controlled by a regulator gene , which produces a small protein molecule called a repressor.

The repressor binds to the operator gene and prevents it from initiating the synthesis of the protein called for by the operon. The presence or absence of certain repressor molecules determines whether the operon is off or on.

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As mentioned, this model applies to bacteria. The genes of eukaryotes, which do not have operons, are regulated independently. The series of events associated with gene expression in higher organisms involves multiple levels of regulation and is often influenced by the presence or absence of molecules called transcription factors. These factors influence the fundamental level of gene control, which is the rate of transcription, and may function as activators or enhancers.

Specific transcription factors regulate the production of RNA from genes at certain times and in certain types of cells. This single chain of RNA, called messenger RNA mRNA , then passes to the organelles called ribosomes , where the process of translation , or protein synthesis, takes place. Each set of three nucleotides codes for one amino acid.

The series of amino acids built according to the sequence of nucleotides forms a polypeptide chain ; all proteins are made from one or more linked polypeptide chains. Experiments conducted in the s indicated one gene being responsible for the assembly of one enzyme , or one polypeptide chain. This is known as the one gene—one enzyme hypothesis. However, since this discovery, it has been realized that not all genes encode an enzyme and that some enzymes are made up of several short polypeptides encoded by two or more genes. Experiments have shown that many of the genes within the cells of organisms are inactive much or even all of the time.

Thus, at any time, in both eukaryotes and prokaryotes, it seems that a gene can be switched on or off. The regulation of genes between eukaryotes and prokaryotes differs in important ways. The process by which genes are activated and deactivated in bacteria is well characterized. Bacteria have three types of genes: structural, operator, and regulator. Structural genes code for the synthesis of specific polypeptides. Operator genes contain the code necessary to begin the process of transcribing the DNA message of one or more structural genes into mRNA.

Gene Keys – The Synthesis

Thus, structural genes are linked to an operator gene in a functional unit called an operon. Ultimately, the activity of the operon is controlled by a regulator gene , which produces a small protein molecule called a repressor. The repressor binds to the operator gene and prevents it from initiating the synthesis of the protein called for by the operon. The presence or absence of certain repressor molecules determines whether the operon is off or on. As mentioned, this model applies to bacteria. The genes of eukaryotes, which do not have operons, are regulated independently. The series of events associated with gene expression in higher organisms involves multiple levels of regulation and is often influenced by the presence or absence of molecules called transcription factors.


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These factors influence the fundamental level of gene control, which is the rate of transcription, and may function as activators or enhancers. Specific transcription factors regulate the production of RNA from genes at certain times and in certain types of cells. Transcription factors often bind to the promoter, or regulatory region, found in the genes of higher organisms.


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Following transcription, introns noncoding nucleotide sequences are excised from the primary transcript through processes known as editing and splicing. The result of these processes is a functional strand of mRNA. For most genes this is a routine step in the production of mRNA, but in some genes there are multiple ways to splice the primary transcript, resulting in different mRNAs, which in turn result in different proteins. Once it was understood that genes had a discrete chemical identity, it was envisaged that, someday, with work, luck and the right sorts of instruments, knowing all the rest would be possible.

Few geneticists in the s foresaw the development of genetic techniques, to make new things at biochemical, cellular and organismic levels. Genetics first intruded into the public consciousness as eugenics, then as biotech. So one terminus of the history of genetics is the Nasdaq-listed company, but another is a modern mode of self-understanding. Your nerve cells and your liver cells have the same genes, but, as geneticists have understood for a long time, some genes that are turned on in one type of tissue are toggled off in others.

Mukherjee wants us to understand that our genome may also respond to the external environment. Our heredity is our environment at one remove, and the flow of biological information is not a straight line but a circle. But probably not cautious enough: pre-publication excerpts of this book in the New Yorker unleashed a torrent of criticism in the genetics blogosphere, showing just how much scientific and ideological passion the old nature-nurture dispute still retains, and how concerned geneticists are that the public are under the impression that the environment is everything.