molecular biology

1. The branch of biology that deals with the formation, structure, and function of macromolecules essential to life, such as nucleic acids and proteins, and especially with their role in cell replication and the transmission of genetic information.
2. The branch of biology that deals with the manipulation of DNA so that it can be sequenced or mutated. If mutated, the DNA is often inserted into the genome of an organism to study the biological effects of the mutation.

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The study of structural and functional properties of biological systems, pursued within the context of understanding the roles of the various molecules in living cells and the relationship between them. Molecular biology has its roots in biophysics, genetics, and biochemistry. A prime focus of the field has been the molecular basis of genetics, and with the demonstration in the mid-1940s that deoxyribonucleic acid (DNA) is the genetic material, emphasis has been on structure, organization, and regulation of genes. Initially, molecular biologists restricted their studies to bacterial and viral systems, largely because of their genetic and biochemical simplicity. Escherichia coli has been extensively examined because of its limited number of cellular functions and the corresponding restricted amount of genetic information encoded in the bacterial chromosome. Simple eukaryotic cells, such as protozoa and yeast, offer similar advantages and also have been studied. For these same reasons, bacteriophage and animal viruses have provided molecular biologists with the ability to study the structural and functional properties of molecules in intact cells. However, a series of conceptual and technological developments occurred rapidly during the late 1970s that permitted molecular biologists to approach a broad spectrum of plant and animal cells with experimental techniques. One of the major factors has been the development and applications of genetic engineering. Recombinant DNA technology allowed the isolation and selective modification of specific genes, thereby reducing both their structural and functional complexity and facilitating the study of gene expression in higher cells. The concepts and techniques used by molecular biologists have been rapidly and effectively employed to resolve numerous cellular, biological, and biochemical problems—becoming routine at both the basic and applied levels.

The recognition of DNA as the genetic material coupled with the discovery that genes reside in chromosomes resulted in an intensive effort to map genes to specific chromosomes. Initially genes were assigned to chromosomes on the basis of correlations between modifications in cellular function, particularly biochemical defects, and the addition, loss, or modification of specific chromosomes. See also Chromosome aberration; Mutation.

A major breakthrough was the development of somatic cell genetics. This is an approach in which, for example, human and hamster cells are fused, resulting in a hybrid cell initially containing the complement of human and hamster chromosomes. As the cells grow and divide in culture, the hamster chromosomes are retained while there is a progressive loss of human chromosomes. By correlating the loss of human biological or biochemical traits with the loss of specific human chromosomes, a number of human genes have been successfully mapped. See also Somatic cell genetics.

The development of methods for isolating genes and for determining the genetic sequences of the DNA in which the genes are encoded, led to rapid advances in gene mapping at several levels of resolution. Localization of specific genes to chromosomes is routinely carried out with cloned genes as probes. Further information about the segment of a chromosome in which a specific gene resides can be obtained by directly determining the DNA sequences of both the gene itself and the surrounding region.

Chromosome localization of specific genes has numerous applications at both the basic and clinical levels. At the basic level, knowledge of the positions of various genes provides insight into potentially functional relationships. At the clinical level, chromosome aberrations are now routinely used in prenatal diagnosis of an extensive series of human genetic disorders, and several chromosomal modifications have been linked to specific types of cancer. Knowledge of genetic defects at the molecular level has permitted the development of diagnostic procedures that in some instances, such as sickle cell anemia, are based on a single nucleotide change in the DNA.

Recombinant DNA

Recombinant DNA technology has provided molecular biology with an extremely powerful tool. In broad terms, applications of recombinant DNA technology can be divided into four areas—biomedical, basic biological, agricultural, and industrial. Biomedical applications include the elucidation of the cellular and molecular bases of a broad spectrum of diseases, as well as both diagnostic and therapeutic applications in clinical medicine.

In a strictly formal sense, the term recombinant DNA designates the joining or recombination of DNA segments. However, in practice, recombinant DNA has been applied to a series of molecular manipulations whereby segments of DNA are rearranged, added, deleted, or introduced into the genomes of other cells.

The ability to manipulate or “engineer” genetic sequences is based on several developments.

1. Methods for breaking and rejoining DNA. The precise breaking and rejoining of DNA has been made possible by the discovery of restriction endonucleases, enzymes that have the ability to recognize specific DNA sequences and to cleave the double helix precisely at these sites. Also important are the ability to join fragments of DNA together with the enzyme DNA ligase, and the techniques to determine the nucleotide sequence of genes and thereby confirm the identity and location of structural and regulatory sequences.

2. Carriers for genetic sequences. Bacterial plasmids, that is, circular double-stranded DNA molecules that replicate extrachromosomally, have been modified so that they can serve as efficient carriers for segments of DNA, complete genes, regions of genes, or sequences contained within several different genes. Bacteriophage and animal viruses, retroviruses, and bovine papilloma virus have also been successfully utilized as DNA carriers. These carriers are referred to as cloning vectors. Host cells in which vectors containing cloned genes can replicate range from bacteria to numerous other cells, including normal, transformed, and malignant human cells.

3. Introduction of recombinant DNA molecules. Genetic sequences in the form of isolated DNA fragments, or chromosomes, or of DNA molecules cloned in plasmid vectors can be introduced into host cells by a procedure referred to as transfection or DNA-mediated gene transfer—a technique that renders the cell membrane permeable by a brief treatment with calcium phosphate, thereby facilitating DNA uptake. Genes cloned in viruses can also be introduced by infection of host cells.

4. Selection of cells containing cloned sequences. Bacterial cells containing plasmids with cloned genes can be detected by selective resistance or sensitivity to antibiotics. In addition, the presence of introduced genes in bacterial, plant, or animal cells can be assayed by a procedure known as nucleic acid hybridization.

5. Amplification. Amplification of genetic sequences cloned in bacterial plasmids is efficiently achieved by treatment of host cells with antibiotics which suppress replication of the bacterial chromosome, yet do not interfere with replication of the plasmid with its cloned gene. Sequences cloned in bacterial or animal viruses are often amplified by virtue of the ability of the virus to replicate preferentially. See also Gene amplification.

6. Expression. Expression of cloned human genes can be mediated by regulatory sequences derived from the natural gene, from exogenous genes, or by host cell sequences.

Two clinically important genes, human insulin and human growth hormone, have been cloned and introduced into bacteria under conditions where biologically active hormones can be produced.

Progress has been made in applications of recombinant DNA technology to the resolution of agricultural problems, especially for the improvement of both crops and livestock. See also Adenohypophysis hormone; Breeding (animal); Breeding (plant); Genetic engineering; Insulin.

Biophysical analysis

Understanding of the structural properties of molecules and the interaction between molecules that constitute biologically important complexes has been facilitated by biophysical analysis. For example, developments in the resolution offered by techniques such as electron microscopy, x-ray diffraction, and neutron scattering have provided valuable insight into the structure of chromatin, the protein-DNA complex which constitutes the genome of eukaryotic cells. These techniques have also provided clues about modifications in chromatin structure that accompany functional changes. One possible application of biophysical analysis is the diagnosis of human disorders by adaptation of nuclear magnetic resonance for tissue and whole body evaluation of soft tissue tumors, blood flow, and cardiac function. See also Electron microscope; Nuclear magnetic resonance (NMR); X-ray diffraction.

Flow of molecular information

Information for all cellular activities is encoded in DNA; selective elaboration of this information is prerequisite to meeting both structural and biochemical requirements of the cell. In this regard, there are three major areas of investigations by molecular biologists: (1) the composition, structure, and organization of chromatin, the protein-DNA molecular complex in which genetic information is encoded and packaged; (2) the molecular events associated with the expression of genetically encoded information so that specific cellular biochemical requirements can be met; and (3) the molecular signals that trigger the expression of specific genes and the types of communication and feedback operative to monitor and mediate gene control. See also Chromosome; Deoxyribonucleic acid (DNA); Gene; Genetic code; Nucleic acid.

Molecular biology is a branch of biological science that investigates how genes govern the activity of cells, tissues, and organisms. It evolved by the coming together of the sciences of genetics, biochemistry, and cell biology. Its cardinal rule is that DNA makes RNA makes protein.

— Alan W. Cuthbert

See cell; genetics, human.

Molecular Biology is the science, or cluster of scientific activities, that seeks to explain the phenomena of life through investigation of the molecules found in living things. The term was apparently invented in the late 1930s by Warren Weaver, a mathematician-turned official of the Rockefeller Foundation, who from 1933 through World War II (1939–1945) channeled much of this philanthropy's considerable resources into a program to promote medical advances by making the life sciences more like physics in intellectual rigor and technological sophistication. There is considerable debate about the extent to which Weaver successfully altered the intellectual direction of the wide range of life sciences with which he interacted. However, there can be little doubt that his program made important new instruments and methods available for biologists. For instance, Rockefeller support greatly furthered the development of X-ray crystallography, ultracentrifuge and electrophoresis instrumentation, and the electron microscope, all used for analyzing the structure and distribution in organisms of proteins, nucleic acids, and other large biomolecules. In the 1930s and 1940s, these biological macromolecules were studied not mainly by biochemists, since the traditional methods of biochemistry were adequate only for the study of compounds orders of magnitude smaller (with molecular weights in the hundreds), but rather by scientists from the ill-defined fields known as "biophysics" and "general physiology."

A general postwar enthusiasm for science made rich resources available to biologists from federal agencies such as the National Science Foundation and the National Institutes of Health. Thanks to this new funding, and also to a postatomic urge to make physics benefit mankind peacefully, the research topics and methods of biophysicists made great headway in the 1950s. New radioisotopes and accelerators spurred radiobiology. Electron microscopes were turned on cells and viruses. Protein structure was probed by crystallography, electrophoresis, and ultracentrifugation; furthermore, chemical methods were developed allowing determination of the sequence of the string of amino acids making up smaller proteins. This kind of macromolecule-focused research in the 1950s has been described as the "structural school of molecular biology" (or biophysics). In the immediate postwar era, another approach also developed around Max Delbrück, a physicist-turned-biologist fascinated since the 1930s with explaining the gene, who attracted many other physicists to biology. Now regarded as the beginning of molecular genetics, this style has been called the "informational school of molecular biology," since during the 1940s and 1950s the school probed the genetic behavior of viruses and bacteria without any attempt to purify and characterize genes chemically. To the surprise of many, largely through the combined efforts of James Watson and Francis Crick—a team representing both schools—in the mid-1950s, the gene was found to be a double-helical form of nucleic acid rather than a protein. From this point through the early 1960s, molecular geneticists concentrated much of their efforts on "cracking" the "code" by which sequences of nucleic acid specify the proteins that carry out the bulk of biological functions. After the "coding" problem was settled in the mid-1960s, they turned mainly to the mechanisms by which genes are activated under particular circumstances, at first in viruses and bacteria, and from the 1970s, in higher organisms. While the extent to which physics actually influenced the development of molecular biology is controversial, some impact can clearly be seen in the use of cybernetic concepts such as feedback in explaining genetic control, as well as in early thinking about genetics as a cryptographic problem.

Although many projects associated with biophysics flourished in the 1950s, the field as a whole did not. Rather, some areas pioneered by biophysicists, such as protein structure, were partly absorbed by biochemistry, while others split off in new disciplines. For example, electron microscopists studying cell structure split when they established cell biology, and radiobiologists largely left biophysics to join (with radiologists) in the newly emerging discipline of nuclear medicine. By the later 1960s, departments bearing the name "molecular biology" were becoming more common, typically including molecular genetics as well as certain types of "structural" biophysics. In the 1970s a new generation of convenient methods for identifying particular nucleic acids and proteins in biological samples (RNA and DNA hybridization techniques, monoclonal antibodies) brought the study of genes and their activation to virtually all the experimental life sciences, from population genetics to physiology to embryology. Also in the 1970s, methods to determine the sequence of nucleic acids making up genes began to be developed—culminating during the 1990s in the government-funded, international Human Genome Project—as well as methods for rearranging DNA sequences in an organism's chromosomes, and then reintroducing these altered sequences to living organisms, making it possible for molecular geneticists to embark upon "genetic engineering." In the early twenty-first century, there is virtually no branch of life science and medicine that is not "molecular," in that all explain biological phenomena partly in terms of nucleic acid sequences and protein structure. Thus, from its beginnings, molecular biology has resisted definition as a discipline. But however defined—as a style of investigation, a set of methods or questions, or a loosely knit and overlapping set of biological fields based in several disciplines—the enterprise of explaining life's properties through the behavior of its constituent molecules has, since its origins in the interwar era, become one of the most intellectually fruitful and medically useful movements ever to engage the life sciences.

Bibliography

Abir-Am, Pnina. "The Discourse of Physical Power and Biological Knowledge in the 1930's: A Reappraisal of the Rockefeller Foundation's 'Policy' in Molecular Biology," Social Studies of Science 12: 341–382 (1982).

———. "Themes, Genres and Orders of Legitimation in the Consolidation of New Scientific Disciplines: Deconstructing the Historiography of Molecular Biology." History of Science 23 (1985): 73–117.

Chadarevian, Soraya de. Designs for Life: Molecular Biology After World War II. Cambridge, UK: Cambridge University Press, 2002.

Creager, Angela N. H. The Life of a Virus: Tobacco Mosaic Virus As an Experimental Model, 1930–1965. Chicago: University of Chicago Press, 2002.

Kay, Lily E. The Molecular Vision of Life: Caltech, the Rockefeller Vision, and the Rise of the New Biology. New York: Oxford University Press, 1993.

———. Who Wrote the Book of Life?: A History of the Genetic Code. Stanford, Calif.: Stanford University Press, 2000.

Keller, Evelyn Fox. Refiguring Life: Metaphors of Twentieth-Century Biology. New York: Columbia University Press, 1995.

Kohler Jr., Robert E. "The Management of Science: The Experience of Warren Weaver and the Rockefeller Foundation Program in Molecular Biology." Minerva 14 (1976): 279–306.

Olby, Robert C. The Path to the Double Helix. Seattle: University of Washington Press, 1974.

Pauly, Philip. "General Physiology and the Discipline of Physiology, 1890–1935," in G. L. Geison, ed., Physiology in the American Context, 1850–1940. Baltimore: American Physiological Society, 1987, 195–207.

Rasmussen, Nicolas. "The Midcentury Biophysics Bubble: Hiroshima and the Biological Revolution in America, Revisited." History of Science 35 (1997): 245–293.

———. Picture Control: The Electron Microscope and the Transformation of Biology in America, 1940–1960. Stanford, Calif.: Stanford University Press, 1997.

The branch of science devoted to studies of the structure, function, and reactions of DNA, RNA, proteins, and other molecules involved in the life processes.

The study of biology from the viewpoint of the physical and chemical interactions of molecules involved in life functions.

• Branches and Disciplines - molecular biology: study of complex chemistry of biological macromolecules, esp. those involved in genetics

Molecular biology ( /məˈlɛkjʊlər/) is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry. Molecular biology chiefly concerns itself with understanding the interactions between the various systems of a cell, including the interactions between the different types of DNA, RNA and protein biosynthesis as well as learning how these interactions are regulated.

Writing in Nature in 1961, William Astbury described molecular biology as

not so much a technique as an approach, an approach from the viewpoint of the so-called basic sciences with the leading idea of searching below the large-scale manifestations of classical biology for the corresponding molecular plan. It is concerned particularly with the forms of biological molecules and [...] is predominantly three-dimensional and structural—which does not mean, however, that it is merely a refinement of morphology. It must at the same time inquire into genesis and function.^[1]

Contents 1 Relationship to other biological sciences 2 Techniques of molecular biology 2.1 Expression cloning 2.2 Polymerase chain reaction (PCR) 2.3 Gel electrophoresis 2.4 Macromolecule blotting and probing 2.4.1 Southern blotting 2.4.2 Northern blotting 2.4.3 Western blotting 2.4.4 Eastern blotting 2.5 Arrays 2.6 Allele Specific Oligonucleotide 2.7 Antiquated technologies 3 History 4 Clinical significance 5 See also 6 References 7 Further reading 8 External links

Relationship to other biological sciences

Schematic relationship between biochemistry, genetics, and molecular biology

Researchers in molecular biology use specific techniques native to molecular biology but increasingly combine these with techniques and ideas from genetics and biochemistry. There is not a defined line between these disciplines. The figure above is a schematic that depicts one possible view of the relationship between the fields:

• Biochemistry is the study of the chemical substances and vital processes occurring in living organisms. Biochemists focus heavily on the role, function, and structure of biomolecules. The study of the chemistry behind biological processes and the synthesis of biologically active molecules are examples of biochemistry.
• Genetics is the study of the effect of genetic differences on organisms. Often this can be inferred by the absence of a normal component (e.g. one gene). The study of "mutants" – organisms which lack one or more functional components with respect to the so-called "wild type" or normal phenotype. Genetic interactions (epistasis) can often confound simple interpretations of such "knock-out" studies.
• Molecular biology is the study of molecular underpinnings of the processes of replication, transcription, translation, and cell function. The central dogma of molecular biology where genetic material is transcribed into RNA and then translated into protein, despite being an oversimplified picture of molecular biology, still provides a good starting point for understanding the field. This picture, however, is undergoing revision in light of emerging novel roles for RNA.

Much of the work in molecular biology is quantitative, and recently much work has been done at the interface of molecular biology and computer science in bioinformatics and computational biology. As of the early 2000s, the study of gene structure and function, molecular genetics, has been among the most prominent sub-field of molecular biology.

Increasingly many other loops of biology focus on molecules, either directly studying their interactions in their own right such as in cell biology and developmental biology, or indirectly, where the techniques of molecular biology are used to infer historical attributes of populations or species, as in fields in evolutionary biology such as population genetics and phylogenetics. There is also a long tradition of studying biomolecules "from the ground up" in biophysics.

Techniques of molecular biology

Since the late 1950s and early 1960s, molecular biologists have learned to characterize, isolate, and manipulate the molecular components of cells and organisms. These components include DNA, the repository of genetic information; RNA, a close relative of DNA whose functions range from serving as a temporary working copy of DNA to actual structural and enzymatic functions as well as a functional and structural part of the translational apparatus; and proteins, the major structural and enzymatic type of molecule in cells.

For more extensive list on protein methods, see protein methods. For more extensive list on nucleic acid methods, see nucleic acid methods.

Expression cloning

Main article: Expression cloning

One of the most basic techniques of molecular biology to study protein function is expression cloning. In this technique, DNA coding for a protein of interest is cloned (using PCR and/or restriction enzymes) into a plasmid (known as an expression vector). A vector has 3 distinctive features: an origin of replication, a multiple cloning site (MCS), and a selective marker (usually antibiotic resistance). The origin of replication will have promoter regions upstream the replication/transcription start site.

This plasmid can be inserted into either bacterial or animal cells. Introducing DNA into bacterial cells can be done by transformation (via uptake of naked DNA), conjugation (via cell-cell contact) or by transduction (via viral vector). Introducing DNA into eukaryotic cells, such as animal cells, by physical or chemical means is called transfection. Several different transfection techniques are available, such as calcium phosphate transfection, electroporation, microinjection and liposome transfection. DNA can also be introduced into eukaryotic cells using viruses or bacteria as carriers, the latter is sometimes called bactofection and in particular uses Agrobacterium tumefaciens. The plasmid may be integrated into the genome, resulting in a stable transfection, or may remain independent of the genome, called transient transfection.

In either case, DNA coding for a protein of interest is now inside a cell, and the protein can now be expressed. A variety of systems, such as inducible promoters and specific cell-signaling factors, are available to help express the protein of interest at high levels. Large quantities of a protein can then be extracted from the bacterial or eukaryotic cell. The protein can be tested for enzymatic activity under a variety of situations, the protein may be crystallized so its tertiary structure can be studied, or, in the pharmaceutical industry, the activity of new drugs against the protein can be studied.

Polymerase chain reaction (PCR)

Main article: Polymerase chain reaction

The polymerase chain reaction is an extremely versatile technique for copying DNA. In brief, PCR allows a single DNA sequence to be copied (millions of times), or altered in predetermined ways. For example, PCR can be used to introduce restriction enzyme sites, or to mutate (change) particular bases of DNA, the latter is a method referred to as "Quick change". PCR can also be used to determine whether a particular DNA fragment is found in a cDNA library. PCR has many variations, like reverse transcription PCR (RT-PCR) for amplification of RNA, and, more recently, real-time PCR (QPCR) which allow for quantitative measurement of DNA or RNA molecules.

Gel electrophoresis

Main article: Gel electrophoresis

Gel electrophoresis is one of the principal tools of molecular biology. The basic principle is that DNA, RNA, and proteins can all be separated by means of an electric field. In agarose gel electrophoresis, DNA and RNA can be separated on the basis of size by running the DNA through an agarose gel. Proteins can be separated on the basis of size by using an SDS-PAGE gel, or on the basis of size and their electric charge by using what is known as a 2D gel electrophoresis.

Macromolecule blotting and probing

The terms northern, western and eastern blotting are derived from what initially was a molecular biology joke that played on the term Southern blotting, after the technique described by Edwin Southern for the hybridisation of blotted DNA. Patricia Thomas, developer of the RNA blot which then became known as the northern blot actually didn't use the term.^[2] Further combinations of these techniques produced such terms as southwesterns (protein-DNA hybridizations), northwesterns (to detect protein-RNA interactions) and farwesterns (protein-protein interactions), all of which are presently found in the literature.

Southern blotting

Main article: Southern blot

Named after its inventor, biologist Edwin Southern, the Southern blot is a method for probing for the presence of a specific DNA sequence within a DNA sample. DNA samples before or after restriction enzyme digestion are separated by gel electrophoresis and then transferred to a membrane by blotting via capillary action. The membrane is then exposed to a labeled DNA probe that has a complement base sequence to the sequence on the DNA of interest. Most original protocols used radioactive labels, however non-radioactive alternatives are now available. Southern blotting is less commonly used in laboratory science due to the capacity of other techniques, such as PCR, to detect specific DNA sequences from DNA samples. These blots are still used for some applications, however, such as measuring transgene copy number in transgenic mice, or in the engineering of gene knockout embryonic stem cell lines.

Northern blotting

Main article: northern blot

The northern blot is used to study the expression patterns of a specific type of RNA molecule as relative comparison among a set of different samples of RNA. It is essentially a combination of denaturing RNA gel electrophoresis, and a blot. In this process RNA is separated based on size and is then transferred to a membrane that is then probed with a labeled complement of a sequence of interest. The results may be visualized through a variety of ways depending on the label used; however, most result in the revelation of bands representing the sizes of the RNA detected in sample. The intensity of these bands is related to the amount of the target RNA in the samples analyzed. The procedure is commonly used to study when and how much gene expression is occurring by measuring how much of that RNA is present in different samples. It is one of the most basic tools for determining at what time, and under what conditions, certain genes are expressed in living tissues.

Western blotting

Main article: western blot

Antibodies to most proteins can be created by injecting small amounts of the protein into an animal such as a mouse, rabbit, sheep, or donkey (polyclonal antibodies) or produced in cell culture (monoclonal antibodies). These antibodies can be used for a variety of analytical and preparative techniques.

In western blotting, proteins are first separated by size, in a thin gel sandwiched between two glass plates in a technique known as SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis). The proteins in the gel are then transferred to a PVDF, nitrocellulose, nylon or other support membrane. This membrane can then be probed with solutions of antibodies. Antibodies that specifically bind to the protein of interest can then be visualized by a variety of techniques, including colored products, chemiluminescence, or autoradiography. Often, the antibodies are labeled with enzymes. When a chemiluminescent substrate is exposed to the enzyme it allows detection. Using western blotting techniques allows not only detection but also quantitative analysis.

Analogous methods to western blotting can be used to directly stain specific proteins in live cells or tissue sections. However, these immunostaining methods, such as FISH, are used more often in cell biology research.

Eastern blotting

Main article: Eastern blotting

Eastern blotting technique is to detect post-translational modification of proteins.^[3] Proteins blotted on to the PVDF or nitrocellulose membrane are probed for modifications using specific substrates.

Arrays

Main article: DNA microarray

A DNA array is a collection of spots attached to a solid support such as a microscope slide where each spot contains one or more single-stranded DNA oligonucleotide fragment. Arrays make it possible to put down large quantities of very small (100 micrometre diameter) spots on a single slide. Each spot has a DNA fragment molecule that is complementary to a single DNA sequence (similar to Southern blotting). A variation of this technique allows the gene expression of an organism at a particular stage in development to be qualified (expression profiling). In this technique the RNA in a tissue is isolated and converted to labeled cDNA. This cDNA is then hybridized to the fragments on the array and visualization of the hybridization can be done. Since multiple arrays can be made with exactly the same position of fragments they are particularly useful for comparing the gene expression of two different tissues, such as a healthy and cancerous tissue. Also, one can measure what genes are expressed and how that expression changes with time or with other factors. For instance, the common baker's yeast, Saccharomyces cerevisiae, contains about 7000 genes; with a microarray, one can measure qualitatively how each gene is expressed, and how that expression changes, for example, with a change in temperature. There are many different ways to fabricate microarrays; the most common are silicon chips, microscope slides with spots of ~ 100 micrometre diameter, custom arrays, and arrays with larger spots on porous membranes (macroarrays). There can be anywhere from 100 spots to more than 10,000 on a given array.

Arrays can also be made with molecules other than DNA. For example, an antibody array can be used to determine what proteins or bacteria are present in a blood sample.

Allele Specific Oligonucleotide

Allele specific oligonucleotide (ASO) is a technique that allows detection of single base mutations without the need for PCR or gel electrophoresis. Short (20-25 nucleotides in length), labeled probes are exposed to the non-fragmented target DNA. Hybridization occurs with high specificity due to the short length of the probes and even a single base change will hinder hybridization. The target DNA is then washed and the labeled probes that didn't hybridize are removed. The target DNA is then analyzed for the presence of the probe via radioactivity or fluorescence. In this experiment, as in most molecular biology techniques, a control must be used to ensure successful experimentation. The Illumina Methylation Assay is an example of a method that takes advantage of the ASO technique to measure one base pair differences in sequence.

Antiquated technologies

In molecular biology, procedures and technologies are continually being developed and older technologies abandoned. For example, before the advent of DNA gel electrophoresis (agarose or polyacrylamide), the size of DNA molecules was typically determined by rate sedimentation in sucrose gradients, a slow and labor-intensive technique requiring expensive instrumentation; prior to sucrose gradients, viscometry was used.

Aside from their historical interest, it is often worth knowing about older technology, as it is occasionally useful to solve another new problem for which the newer technique is inappropriate.

History

Main article: History of molecular biology

While molecular biology was established in the 1930s, the term was first coined by Warren Weaver in 1938. Warren was the director of Natural Sciences for the Rockefeller Foundation at the time and believed that biology was about to undergo a period of significant change given recent advances in fields such as X-ray crystallography. He therefore channeled significant amounts of (Rockefeller Institute) money into biological fields.

Clinical significance

Clinical research and medical therapies arising from molecular biology are partly covered under gene therapy^{[citation needed]}

This section requires expansion.

The use of molecular biology or molecular cell biology approaches in medicine is now called Molecular Medicine.

See also

• Genome
• Proteome
• Molecular microbiology
• Molecular modeling
• Protein structure prediction
• Protein interaction prediction
• Central Dogma of Molecular Biology

References

1. ^ Astbury, W.T. (1961). "Molecular Biology or Ultrastructural Biology?" (PDF). Nature 190 (4781): 1124. doi:10.1038/1901124a0. PMID 13684868. http://www.nature.com/nature/journal/v190/n4781/pdf/1901124a0.pdf. Retrieved 2008-08-04. 
2. ^ Thomas, P.S. (1980). "Hybridization of denatured RNA and small DNA fragments transferred to nitrocellulose". PNAS 77 (9): 5201–5. doi:10.1073/pnas.77.9.5201. ISSN 1091-6490. PMC 350025. PMID 6159641. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=350025. 
3. ^ Thomas S, Thirumalapura N, Crossley EC, Ismail N, and Walker DH (2009). Antigenic protein modifications in Ehrlichia. Parasite Immunology 31, 296-303. [1]

• Cohen, S.N., Chang, A.C.Y., Boyer, H. & Heling, R.B. Construction of biologically functional bacterial plasmids in vitro. Proc. Natl. Acad. Sci. 70, 3240 – 3244 (1973).
• Rodgers, M. The Pandora's box congress. Rolling Stone 189, 37 – 77 (1975).

Further reading

• Keith Roberts, Martin Raff, Bruce Alberts, Peter Walter, Julian Lewis and Alexander Johnson, Molecular Biology of the Cell
• 4th Edition, Routledge, March, 2002, hardcover, 1616 pages, 7.6 pounds, ISBN 0-8153-3218-1
• 3rd Edition, Garland, 1994, ISBN 0-8153-1620-8
• 2nd Edition, Garland, 1989, ISBN 0-8240-3695-6

External links

• Biochemistry and Molecular Biology at the Open Directory Project

v d e Gene expression Introduction to genetics General flow: DNA > RNA > Protein special transfers (RNA > RNA, RNA > DNA, Protein > Protein) Genetic code Transcription (Transcription factors, RNA Polymerase,promoter) Prokaryotic / Archaeal / Eukaryotic post-transcriptional modification (hnRNA,5' capping,Splicing,Polyadenylation) Translation (Ribosome,tRNA) Prokaryotic / Archaeal / Eukaryotic post-translational modification (functional groups, peptides, structural changes) Gene regulation epigenetic regulation (Genomic imprinting) transcriptional regulation post-transcriptional regulation (sequestration, alternative splicing, miRNA) translational regulation post-translational regulation (reversible, irreversible)

v d e Branches of Biology Anatomy · Astrobiology · Biochemistry · Biogeography  · Biomechanics · Biophysics · Bioinformatics · Biostatistics · Botany · Cell biology · Cellular microbiology · Chemical biology · Chronobiology · Conservation biology · Developmental biology · Ecology · Epidemiology · Epigenetics · Evolutionary biology · Genetics · Genomics · Histology · Human biology · Immunology · Marine biology · Mathematical biology · Microbiology · Molecular biology · Mycology · Neuroscience · Nutrition · Origin of life · Paleontology · Parasitology · Pathology · Pharmacology · Physiology · Quantum biology · Systematics · Systems biology · Taxonomy · Toxicology · Zoology

v d e Molecular biology Computational biology  • Developmental biology  • Functional Biology Overview Dogma History of molecular biology • DNA Replication (DNA), Transcription (RNA) - Translation (protein) Element (Genetic • Heredity) Promoter (Pribnow box, TATA box) • Operon (gal operon, lac operon, trp operon) • Intron • Exon • Terminator • Enhancer • Repressor (lac repressor, trp repressor) • Silencer • Histone methylation Linked Life Cell Biology • Biochemistry • Computational Biology • Genetics Engineering Concept mitosis • cell signalling • Post-transcriptional modification and Post-translational modification • Dry Lab/Wet lab Technique Cell culture • model organisms (such as C57BL/6 mice) • method (Nucleic acid • Protein) • Fluorescence, Pigment & Radioactivity High-throughput Technique (-omics): DNA microarray • Mass spectrometry • Lab-on-a-chip Gene regulation Epigenetic • genetic • post-transcriptional • post-translational regulation Glossary

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