What is the bi-directional semi-conservative process

DNA replication - DNA replication

DNA replication: The double helix is ​​unpacked and then shortened. The stranded strand (turquoise) serves as a template for the replication of a new partner strand (green). Nucleotide (bases) are taken separately in order to synthesize the new partner strands into two new double helices.

In molecular biology it is DNA replication the biological process for the production of two identical DNA replicas from a separate DNA molecule. DNA replication takes place in all existing organisms, which is considered to be the most critical part for controlling. The cell possesses the distinctive view of division that makes replication of DNA.

DNA consists of a double helix made up of two complementary strands. These strands are owned by replication. Each strand of the particular DNA possession then serves as a template for making its counterparts, a process that is called semi-conservative replication. In semi-conservative replication, the new helix is ​​made up of its own DNA strand and a new synthetic strand. Cellular proofreading and error checking mechanisms test a legal fidelity solution for DNA replication.

In a cell, DNA replication begins in places. or origins of replication in the genome. Unwinding DNA at the origin and synthesizing new strands obtained from an enzyme known as a helicase cause replication forks to grow bidirectionally from the origin. A number of interests are linked to the fork of replication, including the initiation and continuation of DNA synthesis. What is most well known is that DNA polymerase synthesizes the new strands, compensating for the addition of nucleotide that act on each (template) strand. DNA replication affects the S stage of the interphase.

. DNA replication can also be done in vitro. DNA polymerases isolated from cells and artificial DNA primers can be used to initiate DNA synthesis with known relationships in a template DNA set. Polymerase chain reaction (PCR), ligase chain treatment (LCR), and transcription-mediated amplification (TMA) are examples.

DNA structure

DNA's ability as a double-stranded structure, possible both strands are curled together to form the characteristic double helix. Every single strand of DNA is a chain of four types of nucleotides. The nucleotide in DNA contains a deoxyribose sugar, a phosphate and a nucleobase. The four types of nucleotide love the four nucleobases adenine, cytosine, guanine and thymine, abbreviated as A, C, G and T for practice. Adenine and guanine are purine bases, paid cytosine and thymine are pyrimidine. This nucleotide formation phosphodiester bonds, the phosphate deoxyribose backbone of the DNA double helix with the nucleobases inward (gest. H. In the direction of the same behavior strand) is developed. Nucleobases are definitely juggled between strands to form base pairs. Adenine pairs with thymine (two mechanism bridges) and guanine pairs with cytosine (three right bridges).

DNA strands are directivity and the different ends of the same strand are referred to as the "3 'end (three prim end)" and "5' end (five prim end)". If the base sequence is a different strand of DNA, the left end of the sequence is the 5 'end and the right end of the sequence is the 3' end. The strands of the double helix are antiparallel, one from 5 'to 3' and the other lying strand 3 'to 5'. These terms refer to the feeling atom in deoxyribose that binds the phosphate in the chain. Directionality in DNA synthesis, since DNA polymerase can only synthesize DNA in one direction, nucleotide has to be added at the 3 'end of a DNA strand.

The pairing of complementary bases in DNA (through binding) means that the information in each strand of information is superfluous. Phosphodiester bonds (intra-strand relationships) are trust rather than rights relationships. The strands can become perceptual. The nucleotides on a single strand can be used to reconstruct nucleotides on a newly synthesized partner strand.

DNA polymerase

DNA polymerases add the nucleotide and the 3 'end of a DNA strand. If a mismatch is heard, the polymerase and any further is prevented. Proofreading removes the unseen nucleotide and the rights move on.

DNA polymerases are a family of enzymes that perform all forms of DNA replication. In general, DNA polymerases cannot initiate the synthesis of new strands, only a DNA or RNA strand effect that is paired with a template strand can. To begin synthesis, a short RNA fragment, which will act as a primer, must be paired with the template DNA strand.

DNA polymerase has received a new strand of DNA, replacing the 3 'end of another nucleotide chain and adding new nucleotides that are successively managed by

In general, DNA polymerases are very accurate with an intrinsic error rate of less than one error for every 10 nucleotides heard. DNA polymerases also proofread. You can remove nucleotides from the end of a possible strand to remove unsold bases. Affected Repair Repair mechanisms for mismatches after replicating the DNA for errors and mismatches in the new synthetic DNA strand from the current strand sequences. Taken together, these three differentiation steps are a replication fidelity of less than one error per 10 authorized nucleotides.

The right of DNA replication in a cell different from that of the phage T4 DNA was found in phage-infected E. coli. Equal to the period of exponential DNA rights at 37 ° C, the rate corresponds to 749 nucleotides per second. The mutation rate for the base pair for replication of phage T4 DNA synthesis helps 1.7 per 10.

Replication process

About the steps involved in DNA replication
Steps in DNA synthesis

DNA replication, such as all possible polymerization processes occur in three enzymatic catalyzed and coordinated relationships: initiation, relationships, and relationships.


Role of the initiators in initiating DNA replication.
Formation of a pre-replication complex.

In order for a cell to be in place, it has to replicate its DNA. DNA replication is an all-or-nothing process. Once replication begins, it is closed. This is the case that they are no longer in the same cell cycle. This is done by dividing the initiation of the pre-replication complex.

Pre-replication complex

enables. The consequence of mitosis and early G1 phase is a great deal of complexity of the initiator protein, which is composed in DNA into the pre-replication complex known as the "mode of origin". In E. coli the possible initiator protein is DnaA; in yeast the origin recognition complex dies. Those used by initiator proteins are part of being "AT-rich" since AT base pairs two important bridge bonds and (and the three formed in a CG pair) and the following can be stranded. In eukaryotes, the origin recognition complex catalyzes the assembly of initiator proteins to form the pre-replication complex. Cdc6 and Cdt1 then quota with the bound origin recognition complex at the origin to form a confidence complex, the loss to load the Mcm complex onto the DNA. The Mcm complex is the helicase that resolves the DNA helix and the origins of replication and forks of replication in eukaryotes. The Mcm complex is recruited in the G1 phase and loaded onto the DNA by the ORC-Cdc6-Cdt1 complex via ATP-responsible protein remodeling. Loading the Mcm complex onto the original DNA will complete the formation of the complex before replication.

If the environmental conditions are right in the G1 phase, G1 and G1 / S will become cyclin - Cdk complexes that stimulate the expression of genes that encode components of the DNA synthesis machinery. The G1 / S-Cdk authorizations must also cover the expression and function of S-Cdk complexes, which, depending on the type and cell type, can play a role in activating the origin of replication. The control of these cdks include depending on the cell type and stage of development. This regulation is best seen in bud yeast, where the S-cyclins Clb5 and Clb6 are for DNA replication. Clb5,6-Cdk1 complexes directly authorize origins of replication and are the following S-phase administrations to belong to each origin directly.

In wise way, Cdc7 is also up

Pre-initiation complex

In the early S phase, S-Cdk and Cdc7 are listed, which are used to build the pre-initiation complex, a possible protein complex that will be at the origin. The formation of the pre-initiation complex displaces Cdc6 and Cdt1 from the original replication complex, the pre-replication complex is inactivated and broken down. Loading the pre-initiation complex onto the origin guides the Mcm helicase and causes the DNA helix to unwind. The pre-initiation complex also loads α-primase and other DNA polymerases onto the DNA.

the α-primase is the first primer synthesized hat that transitions the primer template with the clamp loader, which loads the slide clamp onto the DNA to start the DNA synthesis. The components of the pre-initiation complex remain identified with replication forks as they move away from the origin.


DNA polymerase has 5'-3 'activity. All known DNA replication systems become a free 3'-78-hydroxyl group before the synthesis can be completed. The DNA template is read in the 3 'to 5' direction, a new strand is synthesized in the 5 'to 3' direction - this is often refused). Four personal contacts for DNA synthesis are recognized:

  1. All cell-related life forms and many DNA viruses, phages and plasmids use a prase to synthesize a lost RNA primer with a free 3'-OH group that is made by a DNA polymerase.
  2. The retroelements (a retrovirus) have a transfer RNA, the DNA replication through the perception of a free 3'-OH, which is perceived by the reverse possessionase.
  3. is used. In the adenoviruses and the φ29 family of bacteriophages, the 3'-OH group is passed through the side chain of an amino acid of the genome-linked protein (the terminal protein) to the DNA polymerase nucleotides to form a new strand.
  4. In the single stranded DNA viruses - a group that die the zircoviruses, the gemini viruses, the parvoviruses and others - and also the many phages and plasmid that use Rolling Circle Replication (R) CR) mechanism cost the RCR- Endonuclease makes an incision in the genome strand (single-stranded viruses) or in one of the DNA strands (plasmid). The 5 'end of the notched strand is taken to a tyrosine residue on the nuclease, and the free 3' OH group is then used by the DNA polymerase to synthesize the new strand.

The first is the best known of these and is used by cellular relationships. In this mechanism, after separating the two strands of RNA primer, primase belongs to the template strands. The loss strand refers to an RNA primer. The loss strand is affected by the primer by a DNA polymerase with high processing efficiency, the trailing strand becomes discontinuous from each primer that uses Okazaki fragments. RNase removes the primer RNA fragments and a DNA polymerase with some processing action, belonging to the replicative polymerase, steps in to fill in the gaps. When this is complete, you can find a custom incision on the Trailing Strand and multiple incisions on the Trailing Strand. Ligase fills in and out these notches so that the new replication DNA quantity

Die in the process to find yourself between bacteria and archaea / eukaryotes. This means a primase belonging to the protein superfamily DnaG and becoming a TOPRIM fold type catalytic domain. The TOPRIM fold recognizes an α / β core with four conserved strands in a Rossmann guideline topology. This structure is also found in the catalytic relationships of topoisomerase Ia, topoisomerase II, the nucleases of the OLD family, and DNA repair proteins related to the RecR protein.

The primase removed by archaea and eukaryotes related a highly derived version of the RNA recognition motif (RRM). This primase is structurally responsible for many viral RNA-related RNA polymerases, reverse behavior phases, intentional cyclases, and DNA polymerases of the A / B / Y families that are involved in DNA replication and repair. In eukaryotic replication, the primase becomes a complex with Pol α.

paid DNA polymerases take part in the DNA replication process. In E. coli, DNA Pol III is the polymerase enzyme that is concentrated for DNA replication. One of the replication fork is put together to form a replication complex that has an extremely high process function and remains intact for the entire replication cycle. In particular, DNA Pol I is the enzyme that is used to replace RNA primers with DNA. DNA-Pol I has belonged to its Polymerasea belong to an exonucleasea from 5 'to 3' and uses its exonucleasea belongs when the DNA is DNA primer in a nick when it works the loss of DNA strand in a process . Pol I is much less processive than Pol III because its main function in DNA replication is to belong to many short DNA regional differences for a very long longer.

In eukaryotes, the enzyme, Pol α, helps initiate replication by processing a complex with primase. In eukaryotes, it is believed that lead strand synthesis of Pol & epsi; will will; This view was asked when the question was heard on a role of pole δ. The primer removal is treated with Pol δ, the repair of the DNA is lost and the replication is attempted by Pol ε.

when DNA synthesis is heard, the different strands of DNA on each side of the bladder continue to unwind to form a replication fork with two prongs. In bacteria that have a different origin of replication on their own circulating chromosomes, this process has a "theta structure" (determined by the Greek letter theta: θ). In contrast, these include that the eukaryotes change linear chromosomes and initiate replication to belong to origins.

Replication fork

Replication fork scheme.
a: template, b: leading strand, c: trailing strand, d: replication fork, e: primer, f: Okazaki fragments
Many enzymes are on the DNA replication fork.

The replication fork is a structure that belongs to DNA replication. It is passed through helicases, which break the autorbridge bonds that hold the two strands of DNA together in the helix. The right structure will have two branched "prongs" on it, each belonging to its own strand of DNA. These two strands serve as templates for the claims and trailing strands that become when the DNA polymerase matches complementary nucleotides and the templates. The templates can be heard as the leader template and the tail template.

DNA is read by the DNA polymerase in the 3 'to 5' direction, the behavior of the strand was read to be synthesized in the 5 'to 3' direction. Since the matrices of receiving and trailing strand in opposite direction and following are fork of replication, a major problem is how the synthesis of higher (new) trailing strand DNA can be if their direction of synthesis is to withstand the direction of the fork of replication.


The main strand is the strand of the actual DNA that runs in the same direction as the same DNA region. At the beginning of each cycle, the mixture of template and primer is heated, separating the newly synthesized molecule and the template. As the mixture cools, both become templates for annealing new primers and the polymerase extends from them. As a result, the number of copies of the target region doubles per round and increases exponentially. .

See also

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