Chapter 8: Microbial Genetics. 1. Gene Expression. 2. Gene Regulation. 3. DNA Replication & Mutation. 4. Mechanisms of Gene Transfer. Compartments of microbial genetics curriculum. • Basic Genetics. • Genetic variation and gene rearrangements. • Advanced genetics. In accordance with its predecessor, the completely revised and expanded Second Edition of Modern Microbial Genetics focuses on how.
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DNA Replication-occurs at the replication fork. 5' to 3 '. DNA helicase-unzips + parental DNA strand that is used as a template. Leading stand (5' to. The two major and essential functions of genetic material are replication and expression in all organisms. Microbial genetics means genetics of. Microbial. Genetics. CHAPTER SUMMARY. The Structure and Replication of eukaryotic cells use DNA as their genetic material; some viruses use DNA, and.
Introduction The replicon model of Jacob et al. Model for kinetic coupling and catalytic facilitation. Adding dNS deoxynucleosides , dNT deoxynucleotides , or dNDP deoxynucleoside diphosphates enables the precursors to be channeled better than dNTP deoxynucleoside triphosphates, the immediate DNA precursors because they can enter the complex more easily.
It made evolutionary sense that because of the lack of a nucleus in prokaryotes, it was necessary to sequester the many components involved in these events so that they could interact, even though most of them are not, by themselves, membrane proteins. Nevertheless, since the model was proposed, many proteins involved in DNA replication of prokaryotes have been found to require a membrane environment to function, to be activated by components of the membrane, or to be membrane associated for reviews, see Firshein, ; Firshein and Kim, ; Sueoka, Of particular importance in this respect are a significant number of initiation proteins that function in a wide variety of bacteria, plasmids, and bacterial viruses.
They include the all important DnaA protein of E. The requirements for these types of proteins to be concentrated at the origin of replica- 19 tion, coupled with relatively low rates of synthesis in the cell e.
Proof for the membrane as the site for replication has been subject to many difficulties such as confirming that macromolecules observed in a cell lysate represent a natural complex before lysis.
In addition the existence of weak DNA-membrane interactions and the probable temporary nature of many such interactions, as well as a lack of knowledge of membrane receptors for DNA, has caused conflicting interpretations of specific results. Nevertheless, the total weight of support for the replicon-membrane interaction is compelling, consisting of genetic, molecular, ultrastructural, and biochemical analysis.
However, as will be discussed below, both positive and negative models for control of DNA replication by the membrane have been proposed.
Therefore it is not surprising that different organisms display differences in their DNA-membrane interactions. Indeed, it appears that basic differences exist between gram-negative and gram-positive bacteria in this respect, and that other modifications may be present in plasmids and bacteriophages.
Specific Organisms 1. However, it was not until the isolation or detection of the origin of replication that further progress was possible. A number of groups reported that origin region DNA was not only enriched in membrane fractions extracted from E. An important new detail was added in that origin DNA bound to the outer membrane only when it was in a hemimethylated state methylation of only one strand of double-stranded DNA , whereas fully methylated or unmethylated DNA did not Ogden et al.
This region contains many GATC sites recognized by adenine methylase dam sites that are apparently important in mediating the originmembrane interaction.
When additional studies by Landoulsi et al. Such a mechanism in E.
To be sure, it is a membrane event in which newly replicated origins are hemimethylated and transiently sequestered by the outer membrane perhaps with the aid of a Initiation would occur again by release of the sequestered hemimethylated origin from the outer membrane. The dnaA gene is also involved in this model in that in order for it to be transcribed to produce the DnaA protein, the promoter must be fully methylated Braun and Wright, which it is at the time of initiation Ogden et al.
However in a hemimethylated form, the dnaA promoter would be sequestered by the outer membrane and unable to transcribe the gene.
Basic Principles of Microbial Genetics
Recent studies, however, have suggested that the SeqA protein may have other inhibitory functions on both methylated and hemimethylated origins. These include a the interference with open complex formation during initiation Torheim and Skarstad, and b the displacement of the DnaA protein from its origin binding Skarstad et al. Clearly, the relationship between outer membrane binding of oriC, the state of methylation of oriC, and the role of the SeqA protein remains to be elucidated.
Perhaps the most important question in this respect is where initiation is occurring when hemimethylated oriC DNA is remethylated and released from the outer membrane or when the SeqA protein is rendered inactive? In fact, numerous studies in vivo and in vitro have suggested strongly that the DnaA initiation protein functions as a membrane associated protein in a membrane environment Yung and Kornberg, and that anionic phospholipids are vital in maintaining its activity Sekimizu and Kornberg, ; Newman and Crooke, Could it be that replication still occurs in a membrane environment, but in association with the inner membrane and that transfer of oriC between these two domains would control initiation, as suggested by Landoulsi et al.
Some support for this possibility comes from Chakraborty et al who observed oriC binding activity in a small inner membrane subfraction, although the DNA was still in a hemimethylated form.
These techniques have revealed details of genetic organization which traditional genetic methods could not have brought to light. This process is experimental and the keywords may be updated as the learning algorithm improves.
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Amplified origins of antibiotic resistance
I, Bacteria, Bacteriophages and Fungi ed. Author Bios Uldis N. Streips was born in Riga, Latvia and emigrated with his family to the United States in He has been on the faculty of the University of Louisville, School of Medicine since His principal research area is microbial genetics and physiology.
He has 65 peer-reviewed publications and books and chapters. He has received 14 teaching awards at the University of Louisville.
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Streips has mentored 15 Ph. He has run summer workshops for high school teachers for the last 14 years. Free Access. Summary PDF Request permissions.
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Plasmid RK2 Of all the studies concerning the replicon membrane interaction, most of the positive results have been obtained with this broad host range plasmid for review, see Firshein and Kim, With clear appreciation for the impact of molecular genomics, this completely revised and updated edition proves that Modern Microbial Genetics remains the benchmark text in its field. Some support for this possibility comes from Chakraborty et al who observed oriC binding activity in a small inner membrane subfraction, although the DNA was still in a hemimethylated form.
UpperSaddle River: Prentice Hall.
This process is experimental and the keywords may be updated as the learning algorithm improves. Cellular aggregation mediates chromosomal marker exchange and genetic recombination with high frequency. When additional studies by Landoulsi et al. Nevertheless, the total weight of support for the replicon-membrane interaction is compelling, consisting of genetic, molecular, ultrastructural, and biochemical analysis.
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