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DNA and Protein Synthesis - BioTopics
Bacterial deoxyribonucleic acid (DNA) polymerase I is a family of enzymes involved in bacterial DNA synthesis and lesion repair. These enzymes have a multidomain structure, consisting of a single polypeptide chain that encompasses a distinct polymerase domain, a proofreading 3′–5′ exonuclease and/or a 5′–3′ exonuclease activity. Members of the polymerase I family have been investigated extensively, both because of their vital role in replicating and maintaining bacterial chromosomes, and because of their importance as tools in molecular biology, in particular for the polymerase chain reaction (PCR) and DNA sequencing. Studies on the DNA polymerase I in particular have yielded significant insights into the mechanism of DNA polymerisation which is shared by almost all other nucleotide polymerases.
Fifteen human DNA polymerases have been identified. Which of the following statements about them is true?A) They all are involved in DNA replication. B) One of the DNA polymerases opens the replication fork, one forms the primer, another removes the primer, and the rest are involved in protein synthesis. C) The functions of DNA polymerase, helicase, and primase are known; the functions of the others areunknown. D) Each DNA polymerase requires a specific primer to function.E) Most replications are catalyzed by delta and epsilon DNA polymerases; the others are involved in primer removal and DNA repair.
with DNA polymerase δ, is involved in the replication ..
DNA-dependent DNA polymerases synthesize deoxyribonucleic acid (DNA), a role that is central to accurately transmitting genetic material from generation to generation. This family of polymerases functions in a template-dependent manner to insert incoming nucleotides that are encoded by the template onto a growing primer. Polymerases are highly proficient at inserting nucleotides with proper Watson-Crick base pairing. DNA-dependent DNA polymerase exhibits unique roles during DNA replication and DNA repair. This article focuses on the characteristics of prokaryotic and eukaryotic DNA polymerases and the roles of each.
Rothwell PJ, Mitaksov V and Waksman G (2005) Motions of the fingers subdomain of Klentaq1 are fast and not rate limiting: implications for the molecular basis of fidelity in DNA polymerases. Molecular Cell 19: 345–355.
DNA and Protein Synthesis - BioTopics Website
The presence of homologous regions in these diverse polymerases suggests that these enzymes evolved from a common ancestor (See Polymerases for a table of common motifs). All three subfamilies share two common motifs (A and C), whereas only pol I and pol a types also share a third (B). The X-ray crystallographic structure of the Klenow fragment of pol I suggests that motif A is involved in binding the divalent metal cofactor and deoxynucleoside triphosphates (dNTP), motif B is involved in binding the template and bases of the incoming dNTP, and motif C is involved in binding the metal cofactor. The structure of pol b shows DNA bound in an orientation 180° opposite to that observed in the complexes of DNA with HIV-1 reverse transcriptase and with the Klenow fragment (2). Thus, it is thought the pol b and terminal deoxynucleotidyl transferase are evolutionarily distinct from the other DNA-dependent DNA polymerases (3).
Our structural studies of the proteins and nucleic acids involved in translating the gene sequence carried in the messenger RNA into the protein products are providing insights into the translation of the genetic code. This includes our earlier structural studies of aminoacyl-tRNA synthetases, as well as more recent structural studies explaining how the CCA-adding enzyme is able to mature or repair the 3' CCA end of tRNA without using a nucleic acid template. We have established the structures of the CCA-adding enzyme captured in the steps of adding penultimate C and final A as well as the product tRNA.
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DNA Replication and Protein Synthesis - StudyMode
Escherichia coli contains three polymerases, designated DNA pol I, II, and III. 2.1. Pol III The holoenzyme of DNA pol III (Fig. 1) is composed of 10 polypeptide subunits and is present in approximately 15 copies per bacterial cell. It is the principle polymerase responsible for replicating the genome. Pol III is purified either intact or as a core enzyme separate from its accessory factors. The Pol III core consists of the polymerase subunit a (140 kDa; expressed from the DnaE gene; Ref. 4), a proofreading subunit e (28 kDa; from dnaO or mat D gene; Ref. 5), and subunit q (10 kDa; holE). The processivity (i.e., the number of nucleotides synthesized per binding event) of the core enzyme is about 10 (6). This processivity is enhanced to several thousand nucleotides by the addition of subunit b (40 kDa), which functions as a dimer resembling a hexagonal sliding clamp (7). The q subunit (71 kDa) dimerizes readily, which, it is thought, facilitates the interaction of two polymerase core molecules. Evidence suggests that two polymerase core molecules act in concert but in opposite directions to synthesize the leading and lagging strands simultaneously (Fig. 1). The final component of the pol III holoenzyme is the g complex, which is composed of two subunits each of d, d’, g, c, and j. The g complex is a DNA-dependent ATPase that functions as a clamp loader (8). The hydrolysis of ATP facilitates loading of subunit b onto double-stranded DNA.
how are DNA and RNA involved in protein synthesis ..
DNA synthesis proceeds in the 5’ to 3’ direction and requires the presence of dNTPs and primer template DNA. The similar structure of DNA polymerases has indicated that these enzymes use an identical two metal ion-catalyzed polymerase mechanism (Beese and Steitz 1991). One metal ion activates the primer’s 3’-OH for attack on the a-phosphate of the dNTP. The other metal ion stabilizes the negative charge of the leaving oxygen and chelates the b- and g-phosphates (Steitz 1999).
23/03/2015 · Protein Synthesis Within Dna ..
Figure 1. Model of the pol III replication complex during leading and lagging strand synthesis. Dimerization of the t domain facilitates the interaction of two core pol III molecules. This dimerization potentially allows concerted synthesis of both leading and lagging strands by one large polymerase complex. Other proteins that assist during repication in E. coli include DNA B helicase, primase, and single-stranded binding protein (SSB). Arrows show the 5′-3′ direction of polymerization.
and are both involved in the process of protein synthesis
Genes encoded in DNA are transcribed into mRNA by DNA-dependent RNA polymerases that can initiate RNA synthesis at a specific promoter sequence. To understand this process and its regulation and to explain how RNA polymerases differ from DNA polymerases, we have determined the crystal structures of several T7 RNA polymerase complexes with promoter DNAs, mRNAs, and incoming NTP. These structures show how portions of the RNA polymerase recognize the bases in the duplex DNA promoter and denature part of the promoter to form a transcription initiation bubble. In an initiation complex, three nucleotides of transcript are seen base-paired to the template strand. We have also captured this polymerase in a transcription elongation phase as a complex with 30 base pairs of DNA and a 17-nucleotide RNA transcript. The transition from the initiation to the elongation phases of transcription is accompanied by a massive structural rearrangement of the amino-terminal domain, which eliminates the promoter DNA-binding site on the enzyme and creates a tunnel through which the transcript exits the enzyme, thus explaining the high processivity of the elongation phase. Our recent structures of initiation complexes with either a 7- or 8-nucleotide transcript show intermediates in this structural transition in which the promoter binding domain rotates by 45° to accommodate the growing transcript.
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