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  2. Escherichia coli - Wikipedia › wiki › Escherichia_coli


  3. DNA replication in prokaryotes | Microbiology Notes › dna-replication-in-prokaryotes
    • DNA Replication Machinery
    • For DNA Polymerase to Catalyze The Synthesis of DNA, It Needs Three things.
    • DNA Polymerase III Holoenzyme
    • Steps in The Replication Fork
    • Termination of Replication

    DNA replicationis essential to organisms, and a great deal of effort has been devoted to understanding its mechanism. The replication of E. coli DNA requires at least 30 proteins. The overall process of DNA replication is similar in all organisms. Enzymes called DNA polymerases catalyze DNA synthesis. All known DNA polymerases catalyze the synthesis of DNA in the 5′ to 3′ direction, and the nucleotide to be added is a deoxynucleoside triphosphate (dNTP ). Deoxynucleotides are linked by phosphodiester bonds formed by a reaction between the hydroxyl group at the 3′ end of the growing DNA strand and the phosphate closest to the 5′ carbon (the a-phosphate) of the incoming deoxynucleotide. The energy needed to form the phosphodiester bondis provided by release of the terminal two phosphates as pyrophosphate (PPi) from the nucleotide that is added. The PPi is subsequently hydrolyzed to two separate phosphates (Thus the deoxynucleoside triphosphates dATP, dTTP, dCTP, and dGTP serve as DNA...

    The firstis a template, which is read in the 3′ to 5′ direction and is used to direct the synthesis of a complementary DNA strand.
    The second is a primer (e.g., an RNA strand or a DNA strand) to provide a free 3′-hydroxyl group to which nucleotides can be added.
    Thethirdis a set of dNTPs. E. coli has five different DNA polymerases (DNA polymerase I-V). DNA polymerase III plays the major role in replication.

    DNA polymerase III holoenzymeis a multifunctional enzyme composed of 10 different proteins. Most evidence suggests that within the complex are found two core enzymes Each core enzyme binds one strand of DNA and is responsible for catalyzing DNA synthesis and proofreading the product to ensure fidelity of replication. Associated with each core enzyme is a subunit called the 13 clamp. The 13 clamp tethers a core enzyme to the DNA. At the center of the holoenzyme, and represented by an octopus-like structure is a complex of proteins called the clamp loader, which is responsible for loading the 13 clamp onto DNA. A dimer of another protein (tau) holds the holoenzyme together. Because there are two core enzymes, both strands of DNA are bound by a single DNA polymerase III holoenzyme. DNA polymerase III holoenzyme is only one component of a huge complex of proteins called the replisome. Other proteins found in the replisome include helicases, single-stranded DNA binding proteins, and topo...

    In E. coli, DNA replication is initiatedat specific nucleotides called the oriC locus (for origin of chromosomal replication). This site is AT rich. Recall that adenines pair with thymines using only two hydrogen bonds, so AT-rich segments of DNA become single stranded more readily than do GC-rich regions. This is important for initiation of replication. 1. The bacterial initiator protein DnaAis responsible for triggering DNA replication. DnaA proteins bind regions in oriC throughout the cell cycle, but to initiate replication, DnaA proteins must bind a few particular oriC sequences. The presence of DnaA at these sites recruits a helicase (usually DnaB helicase) to the origin. 2. Thehelicase unwinds the helix with the aid of topoisomerases such as DNA gyrase. The single strands are kept separate by SSBs. 3. Primasesynthesizes RNA primers as needed. A single DNApolymerase III holoenzymecatalyzes both leading strand and lagging strand synthesis from the RNA primers. 4. After most of t...

    In E. coli, DNA replication stopswhen the replisome reaches a termination site (ter) on the DNA. A protein called Tus binds to the ter sites and halts progression of the forks. In many other bacteria, replication stops spontaneously when the forks meet. Regardless of how fork movement is stopped, there are two problems that often must be solved by the replisome. One is the formation of interlocked chromosomes called catenanes. The other is a dimerized chromosome-two chromosomes joined together to form a single chromosome twice as long. Catenanes are produced when topoisomerases break and rejoin DNA strands to ease supercoiling ahead of the replication fork. The two daughter DNAmolecules are separated by the action of other topoisomerases that break both strands of one molecule, pass the other DNA molecule synthesis occurs at each replication fork. When replication is complete, a circular molecule has been formed that is twice the length of the parent chromosome. Thus it is a dimeriz...

    • Microbiology Notes
  4. The immunity of the recombinant prokaryotic and eukaryotic ... › science › article

    Apr 01, 2021 · LACK and KMP11 antigens were constructed in prokaryotic (E. coli) and eukaryotic (L. tarentolae) expression systems. • Eukaryotic subunit vaccines showed more effective immunization compared with prokaryotic vaccines. • Protein expression in L. tarentolae by the constructs created in this host contains Post-Translational Modifications.

    • Samira Salari, Iraj Sharifi, Mehdi Bamorovat, Pooya Ghasemi Nejad Almani
    • 2021
  5. RNA polymerase - Wikipedia › wiki › RNA_polymerase

    6 days ago · In most prokaryotes, a single RNA polymerase species transcribes all types of RNA. RNA polymerase "core" from E. coli consists of five subunits: two alpha (α) subunits of 36 kDa, a beta (β) subunit of 150 kDa, a beta prime subunit (β′) of 155 kDa, and a small omega (ω) subunit. A sigma (σ) factor binds to the core, forming the holoenzyme.

  6. Prokaryote - Wikipedia › wiki › Prokaryote


  7. Nucleoid - Wikipedia › wiki › Nucleoid

    3 days ago · The gram-negative bacterium Escherichia coli is a model system for nucleoid research into how chromosomal DNA becomes the nucleoid, the factors involved therein, what is known about its structure, and how some of the DNA structural aspects influence gene expression.

  8. Ribosomal RNA - Wikipedia › wiki › Ribosomal_RNA

    Mar 26, 2021 · In prokaryotes. Similar to eukaryotes, the production of rRNA is the rate-limiting step in the prokaryotic synthesis of a ribosome. In E. coli, it has been found that rRNA is transcribed from the two promoters P1 and P2 found within seven different rrn operons.

  9. Plasmid: Properties, Types, Replication and Organization › plasmid-properties-types

    Mar 21, 2021 · For example: Enterotoxigenic strains of E. coli causes traveler’s diarrhea just because they contains a plasmid which codes for an enterotoxin. Metabolic plasmids This plasmid are holding genes for enzymes that degrade substances known as aromatic compounds (toluene), (2,4-dichlorophenoxyacetic acid), pesticides and sugars (lactose).

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