...Operons Control of Gene Activity in Prokaryotic Cells I. The activity of genes is controlled by the cell and the environment. A. Inducible genes are inactive unless circumstances cause them to be activated (“turned on”). B. Repressible genes are active unless circumstances cause them to be inactivated (“turned off”). C. Constitutive gene functions are active continually, with no control exerted. This is generally an abnormal situation. II. In prokaryotic cells (and viruses) the control of gene activity is often in the form of operons. A. Operons are a form of transcriptional control. B. An operon consists of the structural gene (or genes) which actually code for specific proteins and the controlling elements associated with the control of those genes. An operon typically contains several genes, all under the same control mechanism. C. Though rather similar controlling systems have been found for some eukaryotic genes, control mechanisms in eukaryotes are generally more diverse and more complex, and except for a few examples in simple eukaryotic organisms like yeasts, multiple genes are not found to function under a single control mechanism. In other words, eukaryotic cells do not have operons. III. The first operon investigated was the lac operon in E. coli. This work came from Jacob and Monod (1959 Journal of Molecular Biology V. 1). A. The primary carbohydrate source for the cell is the sugar glucose, but there...
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...by configuring clusters of genes together on the genome into operons that elicit a processive response in the presence of a specific metabolite. The Lac operon is responsible for the cleaving of the disaccharide lactose into two products. A myriad of components control the expression of the Lac operon when two conditions are met. First, the substrate, lactose, must be present. Second, no better substrate for example, glucose, is present (2). The three structural genes in the Lac operon are lacZ, lacY, and lacA. The gene lacZ encodes the tetramer, ß-galactosidase, which is responsible for hydrolyzing the ß-1,4 glycosidic linkage between galactose and glucose in lactose. The transport of lactose into the cell via the enzyme lactose permease is encoded by the gene lacY. The lacA gene encodes the enzyme, galactoside transacetylase, a trimer that transfers an acetyl group from acetyl-CoA to galactosides. Activation of these genes is dependent on the activity of a promoter and three operators based on the nutritional and environmental conditions available to the cell. The lac operon is a negatively controlled inducible operon that utilizes the product of the regulator gene lacI, to repress RNA polymerase from transcribing the lacZYA genes. The three operators involved in the lac operon: O1, O2, and O3 serve as binding sites for lacI and when bound repression is exhibited. Originally, the Jacob-Monod model of the Lac operon proposed only one operator existed. However, with the discovery...
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...PYF12 3/21/05 8:04 PM Page 191 Chapter 12 Gene expression and regulation Bacterial genomes usually contain several thousand different genes. Some of the gene products are required by the cell under all growth conditions and are called housekeeping genes. These include the genes that encode such proteins as DNA polymerase, RNA polymerase, and DNA gyrase. Many other gene products are required under specific growth conditions. These include enzymes that synthesize amino acids, break down specific sugars, or respond to a specific environmental condition such as DNA damage. Housekeeping genes must be expressed at some level all of the time. Frequently, as the cell grows faster, more of the housekeeping gene products are needed. Even under very slow growth, some of each housekeeping gene product is made. The gene products required for specific growth conditions are not needed all of the time. These genes are frequently expressed at extremely low levels, or not expressed at all when they are not needed and yet made when they are needed. This chapter will examine gene regulation or how bacteria regulate the expression of their genes so that the genes that are being expressed meet the needs of the cell for a specific growth condition. Gene regulation can occur at three possible places in the production of an active gene product. First, the transcription of the gene can be regulated. This is known as transcriptional regulation. When the gene is transcribed and how much it is...
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...Problems from textbook 13.18 The streptomycin sensitive strain should be exposed to a mutagen (such as UV light or radiation) to create mutants that may be resistant to streptomycin. Next, prepare a plate that has streptomycin. The bacterial colonies that grow on this plate will all be resistant to streptomycin. Now, make a copy of these colonies using replica plating. Transfer the colonies to a plate that does not contain streptomycin. The colonies that grow on the plate without streptomycin are the strain that can live with or without streptomycin. The colonies that do not grow on the plate without streptomycin cannot live without streptomycin. 13.40 The original polypeptide strain and the double mutant differ in two amino acids. The Lys-Gly amino acids in the original polypeptide become Glu-Arg in the double mutant. The Lys-Gly amino acid sequence is: AAA-GGG By adding a G before the first A in the initial AAA sequence, and by deleting the final G, we get: GAA-AGG The resulting sequence codes for Lys-Arg. The entire nucleotide sequence in the double mutant is: 5’ – AUG CCC UUU GGG GAA AGG UUU CCC UAA—3’ 14.8 There are two genes. Gene 1: mutants 1,2,3,4,5,6,8 Gene 2: mutants 7 14.14 A cis-trans test can be performed to determine whether the two varieties are the results of mutations on the same gene, or on different genes. First, it is necessary to ensure that each white variety is true-breeding. Next, we need...
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...you will describe an operon. There are many examples listed in Chapter 14, but if you want to choose an operon not described in your book, please ask me for approval. Make sure you do not pick the same operon as your classmates; we want to expose ourselves to as many regulation proteins and bacteria as possible. In your initial discussion board post, please include the following: The Tryptophan(trp) Operon 1. Describe an operon, the regulatory proteins, the cellular process and the molecules being “sensed”. 2. Include details about the orientation of the genes and the promoter/operator sequences or activator binding site. 3. Provide details about the repressor/activator and inducer/inhibitor proteins. 4. Explain how the operon helps microbe survive and possibly thrive in its environment. 5. Include details about conditions that trigger expression of the gene(s). 6. Explain when this regulation occurs: During transcription, translation, or posttranslation An operon is the genetic regulatory system found in bacteria and their viruses where genes coding for functionally related protein are clustered along the DNA. This allows protein synthesis to be controlled coordinatly in response to the needs of the cell. The trp operon in E. coli us a negative control repressible system, the trp operon is negative control because the system produces a repressor which functions to turn off the operon. The trp operon is a repressor operon because repression occurs when a critical...
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...1. Cells of all multicellular organisms arise during mitosis from a single cell known as a(n) A) gamete. B) zygote. C) embryo. D) clone. E) fetus. 2. Repressor proteins A) prevent binding of RNA polymerase to DNA. B) can be inactivated by an inducer (lactose). C) provide negative control D) prevent binding of RNA polymerase to DNA and can be inactivated by an inducer such as lactose. E) prevent binding of RNA polymerase to DNA. can be inactivated by an inducer such as lactose, and provide negative control. 3. During genetic modification, A) a prokaryote is changed into a eukaryote. B) a cell takes in DNA from another source. C) a cell’s own DNA is inserted into a plasmid. D) a cell is mutated. 4. What does the figure to the right show? A) gel electrophoresis B) DNA sequencing C) a restriction enzyme producing a DNA fragment D) polymerase chain reaction 5. Which of the following is the region that is the binding site for RNA polymerase? A) heterogeneous nuclear DNA B) repressor gene C) promoter sequence D) operator sequence E) all of these 6. Probes for cloned genes use A) complementary nucleotide sequences labeled with radioactive isotopes. B) certain media with specific antibodies. C) specific enzymes. D) certain bacteria sensitive to the genes. E) all of these 7. When a gene transcription occurs, which of the following is produced? A) more DNA B) protein or polypeptide sequences C) messenger RNA ...
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...Contents Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Chapter 11 Chapter 12 Chapter 13 Chapter 14 Chapter 15 Chapter 16 Chapter 17 Chapter 18 Chapter 19 Chapter 20 Chapter 21 Chapter 22 Chapter 23 Introduction to Biochemistry Water Amino Acids and the Primary Structures of Proteins Proteins: Three-Dimensional Structure and Function Properties of Enzymes Mechanisms of Enzymes Coenzymes and Vitamins Carbohydrates Lipids and Membranes Introduction to Metabolism Glycolysis Gluconeogenesis, The Pentose Phosphate Pathway, and Glycogen Metabolism The Citric Acid Cycle Electron Transport and Oxidative Phosphorylation Photosynthesis Lipid Metabolism Amino Acid Metabolism Nucleotide Metabolism Nucleic Acids DNA Replication, Repair, and Recombination Transcription and RNA Processing Protein Synthesis Recombinant DNA Technology 1 10 27 46 65 85 104 119 137 153 169 185 199 213 227 241 256 269 284 300 315 330 348 Chapter 1 Introduction to Biochemistry 1) Which elements account for more than 97% of the weight of most organisms? A) C, H, N, Mg, O, S B) C, H, N, O, P, S C) C, H, N D) Fe, C, H, O, P E) Ca2+ , K+ , Na+ , Mg 2+ , ClAnswer: B Page Ref: Section 2 2) Proteins in biological membranes may be A) porous. B) attached to the membrane surface. C) span the membrane. D) All of the above E) B and C only Answer: D Page Ref: Section 3 3) Which statement...
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