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Topic: DNA replication

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In the News (Sun 26 May 19)

  Replication of DNA
DNA replication begins with a partial unwinding of the double helix at an area known as the replication fork.
DNA polymerase catalyzes the formation of the hydrogen bonds between each arriving nucleotide and the nucleotides on the template strand.
To replicate such huge molecules as human DNA at this speed requires not one, but many replication forks, forming replication bubbles and producing many segments of DNA strands that eventually meet up together and are joined to form the newly synthesized double helix.
www.ncc.gmu.edu /dna/replicat.htm   (909 words)

  DNA Replication
In general, DNA is replicated by uncoiling of the helix, strand separation by breaking of the hydrogen bonds between the complementary strands, and synthesis of two new strands by complementary base pairing (def).
DNA polymerase enzymes are only able to join the phosphate group at the 5' carbon of a new nucleotide to the hydroxyl (OH) group of the 3' carbon of a nucleotide already in the chain.
The 5' end of the DNA is the one with the terminal phosphate group on the 5' carbon of the deoxyribose; the 3' end is the one with a terminal hydroxyl (OH) group on the deoxyribose of the 3' carbon of the deoxyribose (see Fig.
student.ccbcmd.edu /biotutorials/dna/dnarep.html   (1143 words)

 DNA Replication
DNA replication begins with the "unzipping" of the parent molecule as the hydrogen bonds between the base pairs are broken.
A molecule of a DNA polymerase binds to one strand of the DNA and begins moving along it in the 3' to 5' direction, using it as a template for assembling a leading strand of nucleotides and reforming a double helix.
Replication begins at some replication origins earlier in S phase than at others, but the process is completed for all by the end of S phase.
users.rcn.com /jkimball.ma.ultranet/BiologyPages/D/DNAReplication.html   (845 words)

 DNA Replication
DNA polymerase I is the main polymerase involved in DNA repair, and plays a specialized role in DNA replication, using its 5' to 3' exonuclease activity.
Therefore, at each replication fork, the synthesis of one new DNA strand (the lower one in the figure) is continuous, while synthesis of the other strand must be accomplished in small increments, short stretch after short stretch; this type of synthesis is termed discontinuous.
DNA polymerase I uses its 5' to 3' exonuclease activity to digest away the primer RNA, and replaces the primer with DNA by extending the strand from the adjacent Okazaki fragment.
www.emunix.emich.edu /~rwinning/genetics/replic3.htm   (724 words)

 DNA Replication
In general, DNA is replicated by uncoiling of the helix, strand separation by breaking of the hydrogen bonds between the complementary strands, and synthesis of two new strands by complementary base pairing (def).
DNA polymerase enzymes are only able to join the phosphate group at the 5' carbon of a new nucleotide to the hydroxyl (OH) group of the 3' carbon of a nucleotide already in the chain.
The 5' end of the DNA is the one with the terminal phosphate group on the 5' carbon of the deoxyribose; the 3' end is the one with a terminal hydroxyl (OH) group on the deoxyribose of the 3' carbon of the deoxyribose (see Fig.
faculty.ccbcmd.edu /biotutorials/dna/dnarep.html   (1143 words)

 DNA Replication
DNA Replication answers to the question: "When a cell divides, where the extra DNA comes from?".
In the eukaryotes (organisms with cell that have nucleus) the DNA is formed in two strands, each composed of units called Nucleotides.
The DNA Replication Process is capable of opening the Double Helix and separating the two strands.
www.dnareplication.info   (193 words)

 DNA Structure, Replication and Eukaryotic Chromatin Structure>
DNA replication is semi-conservative, one strand serves as the template for the second strand.
DNA single-stranded binding proteins - These proteins bind to the DNA as a tetramer and stabilize the single-stranded structure that is generated by the action of the helicases.
DNA Ligase - Nicks occur in the developing molecule because the RNA primer is removed and synthesis proceeds in a discontinuous manner on the lagging strand.
www.ndsu.nodak.edu /instruct/mcclean/plsc431/eukarychrom/eukaryo2.htm   (727 words)

 DNA Virus Replication
DNA replication is bidirectional (There are two replication forks per circular DNA genome and replication involves leading/lagging strands, Okazaki fragments, DNA ligase, etc.).
This process of DNA replication is very similar to that which occurs in the host cell - which is not surprising as the virus is using mainly host machinery except for the involvement of the T antigen.
The DNA is replicated by a strand displacement mechanism (figure 11).
pathmicro.med.sc.edu /mhunt/dna1.htm   (3111 words)

 DNA Replication
Although the polymerase reaction that is involved in DNA replication is the same, mechanistically, as the one that we saw in the transcription of structural genes on DNA onto complementary mRNA strands, the overall process of DNA replication is much more complicated.
DNA Gyrase: Introduces negative supercoils to compensate for the strain that results from positive supercoiling at the replication fork in prokaryotes.
The DNA methylation patterns in mammalian gametes are mostly erased at the blastocyst stage of embryonic development.
www.rpi.edu /dept/bcbp/molbiochem/BiochSci/sbello/dna_replicn'.htm   (996 words)

 DNA Structure and Function
DNA is pretty unusual in that it is about the only common molecule capable of directing its own synthesis.
Someone else showed them Franklin’s photographs of DNA x-ray crystallography, and from her pictures, they were able to determine that the structure of DNA was organized into a double spiral or double helix.
First, the DNA code is transcribed to RNA code, which is still in the “language” of nitrogenous bases, except that adenine on the DNA pairs with uracil (in place of thymine) on the RNA.
biology.clc.uc.edu /courses/bio104/dna.htm   (3292 words)

 Steve's place - DNA Replication
Thymidine is specific for DNA synthesis as thymidine is not required for the RNA synthesis that occurs during the rest of the cell cycle.
DNA is not synthesised in the 3′ to 5′ direction, as erroneously shown on the left-hand strand.
DNA replication occurs during S-phase and is initiated at origins of replication.
www.steve.gb.com /science/dna_replication.html   (2668 words)

 DNA Replication   (Site not responding. Last check: 2007-11-07)
However, one of the newly formed DNAs must be synthesized in a 3' to 5' direction (since there are only two possible directions of synthesis and the two daughter strands are synthesized in opposite directions due to the antiparallel arrangement of the double helix).
Fragments of DNA result from this discontinuous method of DNA replication (i.e., synthesis occurs towards the existing daughter DNA and upon the inevitable collision with this strand the DNA polymerase is neither able to continue polymerizing nor stitch together the two adjacent DNA molecules).
Not only are DNA polymerases incapable of polymerizing DNA in the 3' to 5' direction, but they are also incapable of initiating DNA polymerization in the absence of an existing 3' -OH (this has something to do with the DNA polymerases being optimized toward high fidelity sequence duplication---mutation avoidance---rather than high versatility).
www.mansfield.ohio-state.edu /~sabedon/biol1060.htm   (1409 words)

 Biology 4A Student Resources
DNA polymerase travels from the 3' to the 5' end.
Problem: it reaches the replication fork, but the helicase is moving in the opposite direction.
During replication, there are many points along the DNA that are synthesized at the same time (multiple replication forks).
www.biologycorner.com /bio4/notes/DNA-replication.php   (195 words)

 DNA Structure & DNA Replication - Cell Biology
DNA is arranged into a double helix structure where spirals of DNA are intertwined with one another continuously bending in on itself but never getting closer or further away (see diagram to the below right).
Cells do not live forever, and in light of this, they must pass their genetic information on to new cells, and be able to replicate the DNA to be passed on to offspring.
It is said that the replicated DNA is semi-conservative, because it possesses 50% of the original genetic material from its parent.
www.biology-online.org /1/5_DNA.htm   (638 words)

 DNA Replication I
Like all known DNA polymerases, DNA polymerase I requires a primer from which to initiate replication and polymerizes deoxyribonucleotides into DNA in the 5' to 3' direction using the complementary strand as a template.
In 1969, John Cairns isolated a viable mutant (polA) lacking DNA polymerase I activity, an indication that polI is NOT the main enzyme used to replicate DNA.
Interestingly, E. coli temperature-sensitive (conditional lethal) mutants lacking the 5'-to-3' exonuclease activity of DNA polymerase I at non-permissive temperatures (40 degrees C) are NOT viable (remember, the polymerizing activity of DNA polymerase I is dispensible!).
oregonstate.edu /instruction/bb492/lectures/DNAI.html   (1362 words)

 Biofundamentals - DNA Replication
DNA replication and molecular machines: The process of nucleic acid replication involves a number of molecule machines, we will consider only one as an example - the clamp loader.
Once DNA replication begins it is important that the polymerase complex remains attached to the DNA.
Later in the DNA replication process, the RNA primers are digested away, replaced with DNA, and joined together to produce a single, uninterrupted replicated strand.
www.virtuallaboratory.net /Biofundamentals/lectureNotes/Topic3-7_replication.htm   (934 words)

 DNA and Molecular Genetics
DNA had been proven as the genetic material by the Hershey-Chase experiments, but how DNA served as genes was not yet certain.
DNA is a double helix, with bases to the center (like rungs on a ladder) and sugar-phosphate units along the sides of the helix (like the sides of a twisted ladder).
Dispersive replication involved the breaking of the parental strands during replication, and somehow, a reassembly of molecules that were a mix of old and new fragments on each strand of DNA.
www.emc.maricopa.edu /faculty/farabee/BIOBK/BioBookDNAMOLGEN.html   (1834 words)

 DNA Replication
At a specific point, the double helix of DNA is caused to unwind possibly in response to an initial synthesis of a short RNA strand using the enzyme helicase.
DNA polymerase III is used to join the appropriate nucleotide units together.
The replication of DNA is guided by the base pairing principle so that no other heterocyclic amine nucleotide can hydrogen bond and fit correctly with cytosine.
www.elmhurst.edu /~chm/vchembook/582dnarep.html   (851 words)

 DNA Replication
Replication begins with the unwinding of the double helix by an enzyme called helicase.
While eukaryotes had many replication sites in action at once, prokaryotes replicate so quickly that only two, one working in each direction around the ring, are needed.
Bacterial DNA is replicated at a rate of about one million base pairs per minute, while other organisms only range from 500 to 5000 pairs per minute.
library.thinkquest.org /20465/DNArep.html   (305 words)

 A Science Odyssey: DNA Workshop: Replication
Within the nucleus of every cell are long strings of DNA, the code that holds all the information needed to make and control every cell within a living organism.
During DNA replication, special enzymes move up along the DNA ladder, unzipping the molecule as it moves along.
When the enzyme has passed the end of the DNA, two identical molecules of DNA are left behind.
www.pbs.org /wgbh/aso/tryit/dna/replication.html   (318 words)

Note that the issue of entanglement is distinct from the issue of DNA superhelicity or torsional tension, either in the parental template duplex or in the nascent (newly synthesized) daughter duplexes.
If replication is due to independent dimer forks, there would be inevitable entanglement of the two nascent DNA duplexes during replication, and segregation would require a special mechanism independent of the replication process itself to eliminate the entanglements.
In contrast, the red circular structure is intended to represent that portion of the replication fork proteins interacting with the lagging strand of the fork.
www.cchem.berkeley.edu /~jehgrp/symbiologic   (2230 words)

 What is a Cell
DNA replication, or the process of duplicating a cell's genome, is required every time a cell divides.
DNA polymerase begins to move along the DNA strand in the 3' to 5' direction, using the single-stranded DNA as a template.
Because DNA synthesis can only occur in the 5' to 3' direction, a second DNA polymerase molecule is used to bind to the other template strand as the double helix opens.
www.ncbi.nlm.nih.gov /About/primer/genetics_cell.html   (8545 words)

 DNA Replicating Itself
A simplified representation of a DNA molecule separating to form two new molecules.
With the assistance of other enzymes, spare parts available inside the cell are bound to the individual strands following the rules of complementary base pairing: adenine (A) to thymine (T) and guanine (G) to cytosine (C).
Two strands of DNA are obtained from one, having produced two daughter molecules which are identical to one another and to the parent molecule.
www.accessexcellence.org /AB/GG/dna_replicating.html   (132 words)

 Build a DNA Molecule
The structure of DNA is a double helix, much like a ladder that is twisted into a spiral shape.
The uprights of the ladder are the structural backbone of the DNA.
DNA bases characteristically pair G with C, and A with T. Use these pairing rules and the nucleotides below to build a DNA strand containing five base pairs.
learn.genetics.utah.edu /units/basics/builddna   (196 words)

This turns out to be a crucial factor because replication is carried out by the activities of a variety of different enzymes which all function by focusing on one DNA end or another or both.
It is the Tom Cruise, the Julia Roberts, the proverbial bread and butter of replication.
As the DNA is opening up for replication, there will always be an issue of structural stress, which is always addressed by the actions of these remarkable enzymes.
www.scq.ubc.ca /?p=187   (3142 words)

 Dna Factory Guide | Dna Test | dna
DNA replication basically means creating two entire DNA strands for each daughter cell in place of the single parent cell...
DNA testing has three major applications for forensic studies: identification of missing persons; identification of victims of wars, accidents, and natural disasters; and crime investigation...
DNA testing is routinely used in immigration cases to prove whether a child under 18 is a biological child of or, in some cases, is related to an individual with a leave to remain in the UK...
dnafactory.com   (1005 words)

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