Examples of mutagens include tobacco products, radioactive substances, x-rays, ultraviolet radiation and a wide variety of chemicals. Flame Retardants. Identify the mutation as a substitution, an insertion, or a deletion. Effects of Frameshift Mutations: Definitions and Examples, Psychological Research & Experimental Design, All Teacher Certification Test Prep Courses, Basic Terms & Skills in Biological Science, Introduction to Organic Molecules & Heterotrophs, Enzyme Function, Interactions & Regulation, Cell Membrane Model, Components & Transport, Cell Structure, Organelles & Organelle Functions, Transcription, Translation & Protein Synthesis, What is a Point Mutation? Lead Extramural Training Program Director, Training, Diversity, and Health Equity Office. In the long run, all of us are the result of some kind of mutation. Notwithstanding the fact that the vast majority of mutations are decidedly harmful, those induced by irradiation in seeds are of interest to horticulturists as a means of producing new and improved varieties of plants. Physical mutagens, mostly ionizing radiation, can increase the natural mutation rate by 1,000 to 1 million fold, and have been widely used to induce heritable genetic changes. A person couldn't instantly sprout wings or fins because he got a mutation. While mutations often cause harmful disorders, they also increase the genetic diversity of populations. Chemical mutagens: Elements such as arsenic, nickel and chromium are considered to be mutagens. Mutagens represent any agent capable of producing damage to DNA. the absence of the enzyme phenylalanine hydroxylase. In humans, for instance, there are genetic mutations that reduce the risk of type 2 diabetes despite the presence of high-risk factors such as obesity and high blood pressure. Anything in the environment that can cause a mutation is known as a mutagen. The result is a DNA library, a collection of bacterial colonies that together contain the entire genome of a particular organism. Antioxidants such as 2, 3-tert butyl-4-hydroxy-anisole (BHA). In the choice of a suitable dose for the production of mutations, a compromise has to be made between the mutagenic effects and damaging effects of the radiation. Mutations can be caused by a number of different factors. Oncogene 16, 6168 (1998), Connor, F., et al. Radiation exerts its mutagenic effect either directly or by creating free radicals that in turn have mutagenic effects. When this reaction cannot occur, phenylalanine accumulates and is then converted to higher than normal quantities of phenylpyruvate. Chemical Agents: Base analogs. Examples of mutagens are pictured in the Figure below . Anything in the environment that can cause a mutation is known as a mutagen. Somatic . There is currently no treatment, but Tay-Sachs disease can be diagnosed in a fetus by assaying the amniotic fluid (amniocentesis) for hexosaminidase A. The chemical or physical agents that cause mutations are called mutagens. April teaches high school science and holds a master's degree in education. You will be able to define mutagens and explain how they occur by the conclusion of this lesson. Three different types of common mutagens are observed in nature- physical and chemical mutagens agents and biological agents. If a mutation doesn't cause significant harm, then it may be passed down through successive generations. Cytoplasmic & Mitochondrial Inheritance | Types, Examples & Impacts. How Does Acid Rain Affect Plants & Plant Growth? Direct evidence for this supposition finally came when scientists examined cells with defective BRCA1 and BRCA2 genes to determine how they responded to an agent known to cause DNA damage: radiation (Xu et al., 1999; Sharan et al., 1997). This results from the replacement of normal human DNA polymerase with Y-family polymerases that bypass DNA repair mechanisms. Fortunately, humans have two active copies of most genes, which provides some protection against the deleterious effects of mutation. window.__mirage2 = {petok:"5tiSJV6vbkKe_AGFYekvQVfVdWDfC2tUTBKbB8tWi6U-86400-0"}; Radiation, chemicals, and replication errors all can cause mutations. Those that are not, result in a mutation.Thus, mutation is a failure of DNA repair.Mutagens are chemicals or physical factors (such as radiation) that increase the rate of mutation in the cells of bacteria, plants, and . Resources [12] //]]>. Most online reference entries and articles do not have page numbers. Now scientists have found ways of identifying and isolating genes that have specific biological functions and placing those genes in another organism, such as a bacterium, which can be easily grown in culture. When DNA polymerase starts synthesizing, it may miss a base or add an extra one, causing indels. In most cases, the defective gene results in a failure to synthesize a particular enzyme. The nucleotide sequence in DNA may be modified either spontaneously or from exposure to heat, radiation, or certain chemicals and can lead to mutations. The null cells were unable to survive the damage, whereas the normal cells survived, presumably because they retained the capacity to repair radiation-related damage (Figure 2). Silent mutation. Restriction enzymes have been isolated from a number of bacteria and are named after the bacterium of origin. However, whereas nearly all carcinogens are mutagenic, not all mutagens are necessarily . Some of the most common mutagenic agents examples are UV light, X- rays, ROS, alkylating agents and base analogy, etc. The incidence of PKU in newborns is about 1 in 12,000 in North America. effects can be achieved through a number of mechanisms. Physical mutagens; Chemical mutagens; Biological mutagens; Physical mutagens: Physical mutagens are X-rays and UV light. Thus, mutations in the BRCA genes have been proposed to allow misregulation of DNA repair possibly leading to tumorigenesis, although other mechanisms have also been proposed. As we've seen in previous lessons, mutations can cause a variety of disorders. The best thing we can do to avoid mutations is to decrease our exposure to mutagens that are found in our environment. Shop Now 37 Rahul Kabir That is, if multiple genes are required for a particular process, damage to even a single copy of one of those genes can damage the entire pathway. Investigation of radiation's mutagenic effects on different tissues, cells, and subcellular compartments is becoming possible by the availability of techniques and tools that allow the precise delivery of small doses of radiation and that provide better monitoring of effects. This page has been archived and is no longer updated. All rights reserved. So, we can thank mutations for the diversity we see in plants and animals today. This is due to the presence of DNA repair mechanisms such as base excision repair (BER), nucleotide excision repair (NER), and mismatch repair (MMR). DNA changes caused by mutagens may harm cells and cause certain diseases, such as cancer. News . These are the Eubacteria (or "true" bacteria ), Eukaryota (the domain that humans, Cell Cycle (Eukaryotic), Genetic Regulation of Sharan's research team in particular demonstrated that cells lacking a wild-type BRCA2 gene were hypersensitive to DNA damaging agents. Each type results in damage to DNA during the processes of replication and repair. Major Consequences with the Radiation Exposure: 1. What are 3 examples of mutagens? An example is the production of human growth hormone, which is used to treat children who fail to grow properly. As would be expected from target theory considerations, X rays and gamma rays given at high doses and high dose rates induce more two-break chromosome aberrations per unit dose than are produced at low doses and low dose rates. Fortunately for us, DNA polymerase always double-checks its work to make sure all the nucleotides have been replicated correctly. Point Mutations | Types, Processes & Effects. Ionizing radiation was the first mutagen that efficiently and reproducibly induced mutations in a multicellular organism. Genome Evolution: Duplication, Rearrangement & Mutation. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Frameshift mutagen ___b. For seven specific genes in the mouse, the doubling dose of gamma radiation for spermatogonia is about 0.3 Gy for high-intensity exposure and about 1.0 Gy for low-intensity exposure. Teratogens can also increase the risk for miscarriage, preterm labor or stillbirth. A mutagen refers to any agent found in an organism's environment capable of producing genetic mutations in DNA. Examples of mutagens are heat and radiation. Journal of Bacteriology 99, 510512 (1969), Moynahan, M. E., et al. It can cause severe DNA damage and lead to cancer or death. - Definition, Causes & Types, Effects of Mutations on Protein Function: Missense, Nonsense, and Silent Mutations, Mutagens: How the Environment Affects Mutation Rates, Point Mutations in DNA: Types, Diseases & Examples, Cell Growth & The Process of Cell Division, Cellular Structure & Processes in Bacteria & Protists, The Musculoskeletal, Circulatory, Respiratory, Digestive & Excretory Systems, Reproduction, Development & Survival in Animals, Mendelian Genetics & Mechanisms of Heredity, Evolutionary Principles & Natural Selection, Principles of Health: Certificate Program, UExcel Basic Genetics: Study Guide & Test Prep, DSST Principles of Physical Science: Study Guide & Test Prep, Introduction to Nutrition: Certificate Program, UExcel Science of Nutrition: Study Guide & Test Prep, UExcel Weather and Climate: Study Guide & Test Prep, Weather and Climate Science: Certificate Program, Introduction to Physical Geology: Help and Review, Causes of Mutation and DNA Damage- Mutagens, Effects of Interionic Attraction on Colligative Properties & Solubility. World of Microbiology and Immunology. . Mutation Spontaneous Mutation & Induced Mutation Mutagen ChemicalMutagens Radiation BiologicalMutagens Conclusion Introduction 3. In base excision repair, a damaged base is removed from the DNA during the G1 stage of the normal cell cycle. Aromatic amines are mutagens that can cause bladder cancer. Although, various mutagens (physical and chemical) are used for the induction of mutation, physical mutagens (radiation: gamma rays and X . Cells generally attempt to fix such breaks by a process called Prior to the 1960s, 85% of patients with PKU had an intelligence quotient (IQ) less than 40, and 37% had IQ scores below 10. p53 is a transcription factor that induces the expression of DNA-repair genes. 24 chapters | For instance, males have only one copy of the genes carried on the X chromosome, and an entire copy of this chromosome is silenced in females. cell's DNA. One way this Their impact also affects lipids and proteins. The dogs offer a way to map radiation across the exclusion zone and study the ongoing effects of the accident. The word 'mutagen' comes from the word part 'gen,' which is found in lots of scientific terms. Mutations are more likely to form when an organism is exposed to a mutagen. X-rays originate through the source of accelerating electrons, while -rays, -rays and -rays originate through atomic nuclei. Specifically, these amoebae secrete certain molecules that organize their movement, causing them to line up and march like soldiers to a single, central destination (Figure 1; Kessin, 2003). Drugs, medicine, chemicals, certain infections and toxic substances are examples of teratogens. Without this enzyme, a person cannot convert phenylalanine to tyrosine, which is the precursor of the neurotransmitters dopamine and norepinephrine as well as the skin pigment melanin. All other trademarks and copyrights are the property of their respective owners. On rare occasions, however, the nucleotide sequence in DNA may be modified either spontaneously (by errors during replication, occurring approximately once for every 10 billion nucleotides) or from exposure to heat, radiation, or certain chemicals. Tobacco taken in the form of snuff contains mutagens that can cause nose tumors. Biological mutagens. Ethylene Dibromide. Create your account. The role of gene interactions in the etiology of human disease is therefore a critical area of study. On the other hand, there are plenty of cases of advantageous mutations. A mutation occurred in the gene, making the sequence 5ATGAGCGACCTTCGCCCATTA3. For example, exposure to UV light can result in the formation of a covalent bond between two adjacent thymines on a DNA strand, producing a thymine dimer (Figure \(\PageIndex{2}\)). Examples of mutagens include radioactive substances, x-rays, ultraviolet radiation, and certain chemicals. Cite this article Pick a style below, and copy the text for your bibliography. Therefore, its best to use Encyclopedia.com citations as a starting point before checking the style against your school or publications requirements and the most-recent information available at these sites: http://www.chicagomanualofstyle.org/tools_citationguide.html. We have seen that the sequence of nucleotides in a cells deoxyribonucleic acid (DNA) is what ultimately determines the sequence of amino acids in proteins made by the cell and thus is critical for the proper functioning of the cell. It's the No. resulting in damage. Mutagens are often also carcinogen s, agents that cause cancer. n., plural: silent mutations. Isolating the specific gene or genes that cause a particular genetic disease is a monumental task. DNA polymerase normally matches the daughter nucleotides to the parent strand and corrects any mistakes through a proofreading step. In turn, this results in the transformation of healthy cells to precancerous cells (carcinogenesis) or the production of cancer cells. https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/radiation-mutagenesis, "Radiation Mutagenesis While many mutations are considered harmful to organisms, mutations also represent the primary source of genetic diversity in populations and thus contribute to the process of evolution. This rate of increase is not large enough to detect with existing methodology in the children of the atomic-bomb survivors of Hiroshima and Nagasaki, owing to their limited numbers and the comparatively small average dose of radiation received by their parents. Exposure to a mutagen can produce DNA mutations that cause or contribute to certain diseases. Remember that all mutations are changes in the nucleotide sequence of DNA. External factors like radiation and chemicals are called mutagens. Some of the common examples of mutagens are- UV light, X-rays, reactive oxygen species, alkylating agents, base analogs, transposons, etc. Mutagens refer to various physical or chemical agents which greatly enhance the frequency of mutations. Mutations are often caused by chemicals, radiation or dangerous substances. B) not all mutations are beneficial. The creation of the thymine dimer prevents the double helix from forming wherever this dimer exists in the nucleotide sequence. [CDATA[ Examples of chemical mutagens include . . The doubling dose for high-intensity exposure in several different organisms has been found experimentally to lie between about 0.3 and 1.5 Gy. Many mutagens, by virtue of their size or structure, can slip With alpha radiation, ionizations lead to an intense but more superficial and localized deposition of energy. Radiations are the first mutagenic agent reported in 1920. See also Evolution and evolutionary mechanisms; Evolutionary origin of bacteria and viruses; Immunogenetics; Molecular biology and molecular genetics; Phage genetics; Radiation resistant bacteria; Radioisotopes and their uses; Viral genetics. Immune System Overview & Function|What is the Immune System? orchestrating changes in genes or gene usage. Plus, get practice tests, quizzes, and personalized coaching to help you Alkylators, one type of chemical. DNA replication. DNA repair mechanisms in response to the mutagenic effect. This content is currently under construction. through a variety of mechanisms. She has taught a combination of ESL and STEM courses to secondary and university students. Learn what a mutagen is. A mutagen that causes the formation of highly reactive ions 2. Phenylalanine (UUU) would be replaced with leucine (CUU). regions of DNA. Formerly, human growth hormone was available only in tiny amounts obtained from cadavers. A germ cell thus affected may be capable of taking part in the fertilization process, but the resulting zygote may be incapable of full development and may therefore die in an embryonic state. The term mutagenic is defined as the ability to induce genetic changes in the DNA of an organism. 6 Sponsored by PureCare Knee Protector Why are knee surgeons excited about this breakthrough knee strap? Well, a mutagen is any chemical substance or physical event that can cause genetic mutations. Is UV radiation an example of a physical mutagen or a chemical mutagen? Any chemical or physical change that alters the nucleotide sequence in DNA is called a mutation. Reactive oxygen species released in irradiated cells are believed to act directly on nuclear DNA and indirectly by modifying bases that will be incorporated in DNA, or deactivating DNA repair enzymes . Cells can be seen migrating (some individually, and some in streams) toward a central point. Do mutations destroy information? In such cases the altered DNA sequence is lost and will not be copied into daughter cells. What effect, if any, an increase in the frequency of chromosome aberrations may have on the health of an affected individual is uncertain. During this cascade, receptor-ligand binding leads to molecular changes in the receptor that are, in turn, passed along to other intracellular proteins. An example of DNA damage caused by UV radiation. When appropriate genes are successfully inserted into E. coli, the bacteria can become miniature pharmaceutical factories, producing great quantities of insulin for people with diabetes, clotting factor for people with hemophilia, missing enzymes, hormones, vitamins, antibodies, vaccines, and so on. (February 22, 2023). Germline mutations occur in gametes. Radon This gas occurs in small amounts in nature, where it's harmless. Breast Cancer Research 7, 2132 (2005), Scully, R., et al. General characteristics agents are known as mutagens, and they act by directly altering a cell's These are discussed as follows: (1) Physical Mutagens: Physical mutagens include various types of radiation, viz. Examples of mutagens include radioactive substances, x-rays, ultraviolet radiation, and certain chemicals. Examples of mutagens are shown in the figure below. Describe how intercalation can affect protein-coding genes Intercalation distorts the shape of DNA, causing polymerase to "slip" off (slippage). C) not all mutations cause visible change. Examples of mutagens are pictured in the Figure below . Exposure to mutagen s can cause induced mutation s, which are various types of chemical agents or radiation . Most of these changes are quickly repaired. [Figure 2] Examples of Mutagens. Does radiation alter DNA? Another gene that has been cloned is the gene for epidermal growth factor, which stimulates the growth of skin cells and can be used to speed the healing of burns and other skin wounds. One example of cell signaling involves the migration of single-celled amoebae of the slime mold Dictyostelium into a single, cooperative fruiting body. converts a normal cell to cancerous cell. A portion of the coding strand of a gene was found to have the sequence 5ATGAGCGACTTTCGCCCATTA3. What are 3 types of mutagens? Carcinogens are those agents that lead to cancer, i.e. Encyclopedia.com. Early evidence that suggested these genes were involved in DNA repair was mostly circumstantial. The genetic disease xeroderma pigmentosum is caused by a lack of the enzyme that cuts out the thymine dimers in damaged DNA. With these techniques, known as recombinant DNA technology, the ability to cure many serious genetic diseases appears to be within our grasp. It can lead to the formation of a covalent bond between two adjacent thymines on a DNA strand, producing a thymine dimer. Radiation injury, also known as radiation sickness, results from exposure to excessive radiation. X-rays, -rays, -rays and -rays are examples of ionizing radiations, which can induce DNA damage due to their high ionizing property. Radiation damages the spermatogonia and the damaged germ cells could occur for a very long time, perhaps a lifetime. These changes within DNA are called point mutations because only one nucleotide is substituted, added, or deleted (Figure \(\PageIndex{1}\)). 1. When adjoining chromosome fibres in the same nucleus are broken, the broken ends may join together in such a way that the sequence of genes on the chromosomes is changed. Human diseases caused by point mutations include cystic fibrosis, color blindness, Tay-Sachs disease, sickle-cell anemia, and cancer. To unlock this lesson you must be a Study.com Member. In their effects on plants, fast neutrons and heavy particles have been found to be up to about 100 times more mutagenic than X rays. The more sensitive the genes are to radiation, the lower is the doubling dose. These agents can change the way molecules bond and react with one another, which increases the likelihood that a mistake will be made in the nucleotide sequence. All forms of high-energy radiation, ionizing (gamma and cosmic rays, neutrons) and non-ionizing (ultraviolet light) radiation that is capable of disrupting the chemical structure of chromosomes, have been found to be mutagenic. Examples of mutagens include tobacco products, radioactive substances, x-rays, ultraviolet radiation and a wide variety of chemicals. Ultraviolet radiation is an example of a mutagen. environmental cues must have some way of reaching cellular nuclei and NCI's Dictionary of Cancer Terms provides easy-to-understand definitions for words and phrases related to cancer and medicine. People receive DNA sequence. Ques. Nucleotide excision repair occurs during the G1 and G2 stages of the cell cycle and deletes lesions that form on nucleotide sequences in DNA. We said before that mutagens come from the environment. Because an insertion or deletion results in a frame-shift that changes the reading of subsequent codons and, therefore, alters the entire amino acid sequence that follows the mutation, insertions and deletions are usually more harmful than a substitution in which only a single amino acid is altered. environmental cues, such as radiation, can directly exert their impact upon a If the condition is detected, mental retardation can be prevented by immediately placing the infant on a diet containing little or no phenylalanine. Typical mutagens include chemicals, like those inhaled while smoking, and radiation, such as X-rays, ultraviolet light, and nuclear radiation. There are at least fifteen different forms of DNA polymerase that facilitate this process by performing replication, repair, and proofreading of DNA. Artificially induced mutations can be created by physical mutagens, such as X-rays, gamma rays, and neutrons, and chemical mutagens, such as ethyl methanesulfonate (EMS), in plant mutation breeding [ 12 ]. As mentioned above, exposure to the human papillomavirus (HPV) results in an increased risk for cancers of the reproductive tract in both men and women. Changes in DNA caused by mutagens can have a range of effects, depending on where these changes happen to occur within the genome. The roman numeral I indicates that it was the first restriction enzyme obtained from this strain of bacteria. With densely ionizing radiation, by comparison, the yield of two-break aberrations for a given dose is higher than with sparsely ionizing radiation and is proportional to the dose irrespective of the dose rate. DNA breaks. Though a point mutation may seem insignificant at the molecular level, we know that a single insertion, deletion, or base substitution can drastically harm an organism. Both sources induce the creation of free radicals or molecules having unpaired electrons. When UV radiation hits the cells in your body, it can change the way DNA polymerase works and increase the probability of a replication error. Examples of mutagens include radioactive substances, x-rays, ultraviolet radiation, and certain chemicals. Ionizing radiation directly affects DNA structure by inducing DNA breaks, particularly, DSBs. How long the pregnant person was exposed. As the number of mutations increases, so also does the extent of damage to the plants. Chemical mutagens include alkylating agents and base analogues. Plant Breeding and Genetics. Identification of adenosine-3', 5'-monophosphate as the bacterial attractant for myxamoebae of Dictyostelium discoideum. Chromosome breaks often heal spontaneously, but a break that fails to heal may cause the loss of an essential part of the gene complement; this loss of genetic material is called gene deletion. Nonlethal mutations in an egg or sperm cell may lead to metabolic abnormalities or hereditary diseases. Nature 422, 481482 (2003) (link to article), Konijn, T. M., et al. Cloning is accomplished by inserting the individual DNA fragments into phages (bacterial viruses) that can enter bacterial cells and be replicated. An error occurred trying to load this video. (a) The thymine dimer is formed by the action of UV light. The common examples of induced mutations include skin cancers due to continuous exposure to radiation and kidney diseases due to exposure to heavy metals. PKU results from the absence of the enzyme phenylalanine hydroxylase. Is alcohol a mutagen? mutagens and radiation, both of which result in DNA damage, albeit for Types of Mutations Depending on the cells that are affected by the mutagen, mutations can be classified as follows: Somatic mutations Encyclopedia.com. There are many kinds of radiations that can increase mutations. As a member, you'll also get unlimited access to over 88,000 Thus, the first task is to obtain smaller pieces of DNA that can be more easily handled. Radiations can be ionizing or nonionizing. Examples of these different types of mutagens and their potential effects on the human body are explored as part of this lesson. Ionizing radiation is one of the most powerful physical mutagens. Therefore, that information is unavailable for most Encyclopedia.com content. In individuals with harmful mutations to the DNA repair pathways, cells infected with HPV enable the virus to replicate by using these mutations to facilitate viral replication. Nature Genetics 17, 423430 (1997) (link to article), Kessin, R. H. Cell motility: Making streams. Alkylators, one type of chemical mutagen, directly impact bases by creating G (guanine) residues resulting in depurination or loss of a purine. Enter your email address to receive updates about the latest advances in genomics research. This results in the formation of mutations, the primary source of genetic diversity in populations. Mutagens are classified into three categories, i.e., physical mutagens, chemical mutagens and biological mutagens. Skin cells are especially vulnerable to UV radiation because, obviously, they have the most direct exposure to the UV light that comes from the sun. Get unlimited access to over 88,000 lessons. Radiation is another type of environmental mutagen that may cause direct changes in a cell's DNA. What causes mutations and what are some examples? Moreover, gene-gene interactions, or epistasis, can amplify the consequences of partial loss of a single gene. For instance, the expression levels of these genes correlate with cell division, peaking during the S phase, therefore suggesting a role in replication, which is also when DNA repair occurs (Blackshear et al., 1998). In some cases, such as About 1 in 5 of all cancers worldwide is caused by microbes (viruses or bacteria). "Radiation Mutagenesis Except for large deletions, most of these lesions can be repaired to a certain extent, and the lethal and mutagenic effect of radiation is assumed to result principally from incompletely or incorrectly repaired DNA. But remember, the 'environment' for an organism is nothing more than the chemical and physical factors surrounding it. Talking Glossary of Genomic and Genetic Terms. 1 cause of lung. An environmental agent that causes a mutation is called a mutagen. When a genetic mutation occurs in the gene for the enzyme hexosaminidase A, for example, gangliosides cannot be degraded but accumulate in brain tissue, causing the ganglion cells of the brain to become greatly enlarged and nonfunctional. Molecular Cell 3, 389395 (1999), Atavism: Embryology, Development and Evolution, Epistasis: Gene Interaction and the Phenotypic Expression of Complex Diseases Like Alzheimer's, Genetic Diagnosis: DNA Microarrays and Cancer, Imprinting and Genetic Disease: Angelman, Prader-Willi and Beckwith-Weidemann Syndromes, Obesity, Epigenetics, and Gene Regulation, Environment Controls Gene Expression: Sex Determination and the Onset of Genetic Disorders, Environmental Cues Like Hypoxia Can Trigger Gene Expression and Cancer Development, Environmental Factors Like Viral Infections Play a Role in the Onset of Complex Diseases, Environmental Influences on Gene Expression, Environmental Mutagens, Cell Signalling and DNA Repair, Gene Expression Regulates Cell Differentiation, The Complexity of Gene Expression, Protein Interaction, and Cell Differentiation, Negative Transcription Regulation in Prokaryotes, Positive Transcription Control: The Glucose Effect, Regulation of Transcription and Gene Expression in Eukaryotes, The Role of Methylation in Gene Expression, Transcription Factors and Transcriptional Control in Eukaryotic Cells, Do Transcription Factors Actually Bind DNA? 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