Monthly Archives: April 2013

GH3 - DNA 2 - *PREVIEW*
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GH3 - DNA 2 - *PREVIEW* - Video

Washington, April 2 (ANI): For the first time, scientists have "discovered how a key step in human DNA replication is performed."

Part of the DNA replication process-in humans and in other life forms-involves loading of molecular structures called sliding clamps onto DNA.

This crucial step in DNA replication had remained somewhat mysterious and had not been well studied in human DNA replication.

Mark Hedglin, a post-doctoral researcher in Penn State University's Department of Chemistry and a member of Benkovic's team, explained that the sliding clamp is a ring-shaped protein that acts to encircle the DNA strand, latching around it like a watch band.

The sliding clamp then serves to anchor special enzymes called polymerases to the DNA, ensuring efficient copying of the genetic material. "Without a sliding clamp, polymerases can copy very few bases-the molecular 'letters' that make up the code of DNA-at a time.

But the clamp helps the polymerase to stay in place, allowing it to copy thousands of bases before being removed from the strand of DNA," Hedglin said.

Hedglin explained that, due to the closed circular structure of sliding clamps, another necessary step in DNA replication is the presence of a "clamp loader," which acts to latch and unlatch the sliding clamps at key stages during the process.

"The big unknown has always been how the sliding clamp and the clamp loader interact and the timing of latching and unlatching of the clamp from the DNA," said Hedglin.

"We know that polymerases and clamp loaders can't bind the sliding clamp at the same time, so the hypothesis was that clamp loaders latched sliding clamps onto DNA, then left for some time during DNA replication, returning only to unlatch the clamps after the polymerase left so they could be recycled for further use," he added.

The study was recently published in the journal eLife. (ANI)

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Elusive step in human DNA replication process demystified

Apr. 2, 2013 New study published in Reproductive Biomedicine Online shows that fluid-filled cavity in 5-day old human blastocysts may contain DNA from the embryo, allowing diagnosis of genetic disease without a biopsy.

Preimplantation genetic diagnosis (PGD) technologies allow identification of genetic disorders in human preimplantation embryos after in vitro fertilization (IVF) and before the embryo is transferred back to the patient. This technique allows couples with a high-risk of passing on inherited diseases, to increase their chances of having a healthy baby. Despite the theoretical benefits of PGD, clinical outcomes using these technologies vary, possibly because of the need to remove one or more cells from the embryo using biopsy.

In a recent study published in Reproductive Biomedicine Online, a group of researchers from Italy and the United Kingdom sought to achieve diagnose of genetic disease in embryonic DNA without the use of a biopsy. By extracting fluid from human embryos at the blastocyst stage they found that it contains DNA from the embryo. Blastocysts are 5 or 6 day old embryos and are at the last free-living stage that can be studied in the laboratory prior to transfer into the uterus. They contain between 50 and 300 cells that surround a fluid-filled cavity called the blastocoels. The researchers carefully removed fluid from the blastocoel, leaving the cells intact; the sampled blastocysts were subsequently cryopreserved. Analysis of this fluid showed that it contained cell-free DNA in a state good enough to determine several known genes of the sex chromosomes by polymerase chain reaction (PCR); whole genome amplification and followed by analysis using a specialized tool for genetic testing called a DNA microarray were also used and revealed whether the embryos had a normal number of chromosomes -- chromosome abnormalities are one of the main causes of miscarriage and failure of embryos to form pregnancies during IVF treatments.

"This is the first time that embryonic DNA has been detected in the human blastocyst without the use of biopsy," explained lead researchers Dr. Simone Palini Ph.D., from the IVF Unit at Cervesi Hospital in Cattolica, Italy and Dr. Galluzzi from University of Urbino in Italy and Dr. Dagan Wells from University of Oxford, United Kingdom.

"This is a technique that most embryologists can easily master," Dr. Buletti who directs the IVF team at Cervesi Hospital Cattolica and Prof. Magnani, Chairman of the Department of Biomolecular Sciences of the University of Urbino, added. "More work needs to be done to confirm our results, but we hope that this approach will ultimately help infertile couples achieve their dream of having a family. It may also improve the options for families affected by severe inherited conditions, helping them to have healthy babies."

"Even though it is only a preliminary finding, this approach may allow for genetic testing of the embryo without the complexity of cell sampling," Dr. Joe Leigh Simpson MD, Senior Vice President for Research Programs, March of Dimes Foundation and President, International Federation of Fertility Societies (IFFS), a pioneer in reproductive medicine and genetics, commented on the research.

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The above story is reprinted from materials provided by Elsevier.

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Sampling of embryonic DNA after IVF without biopsy

April 2, 2013

redOrbit Staff & Wire Reports Your Universe Online

Scientists at Penn State University have discovered how a vital step in the human DNA replication process the loading of molecular structures known as sliding clamps onto DNA molecules is performed.

The researchers say their work, the results of which were published in Tuesdays edition of the journal eLife, will help uncover some of the mystery surrounding this crucial part of the chemical replication process. This step had not previously been closely analyzed in human DNA replication, which is the basis for biological inheritance in all types of living organisms.

According to Mark Hedglin, a post-doctoral researcher in Penn States Department of Chemistry and one of the investigators behind the discovery, the sliding clamp is a ring-shaped protein which essentially encircles a DNA strand, latching around it much like a watch band. The sliding clamp then anchors polymerases enzymes involved in the synthesis of nucleic acids to ensure more efficient copying of the genetic material.

Without a sliding clamp, polymerases can copy very few bases the molecular letters that make up the code of DNA at a time. But the clamp helps the polymerase to stay in place, allowing it to copy thousands of bases before being removed from the strand of DNA, Hedglin explained in a statement.

However, because of the closed circular structure of those sliding clamps, another step in DNA replication the presence of a so-called clamp loader to latch and unlatch them at different stages of the process is required. Previously, researchers did not know exactly how the sliding clamp and the clamp loader interacted with one another, nor did they know exactly when the clamp was attached to or unattached from the DNA.

We know that polymerases and clamp loaders cant bind the sliding clamp at the same time, so the hypothesis was that clamp loaders latched sliding clamps onto DNA, then left for some time during DNA replication, returning only to unlatch the clamps after the polymerase left so they could be recycled for further use, Hedglin said.

In order to test their theory, they turned to a method known as Frster resonance energy transfer (FRET), which attaches fluorescent tags to human proteins and parts of DNA in order to monitor the interactions between them.

With those tags in place, Hedglin said he and his colleagues observed the formation of holoenzymes the active form of the polymerase involved in DNA replication, which consists of the polymerase itself along with any accessory factors that optimize its activity.

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Clamping Down On The Mystery Of Human DNA Replication

ST. LOUIS There is no physical evidence tying Rodney Lincoln to a gruesome attack three decades ago that left a mother dead and her two young daughters critically injured, new DNA tests show.

But theres nothing in those results that points to anyone else in the April 27, 1982, slaying, either.

Among the seven pieces of crime scene evidence sent to a Kansas City crime lab including three bloody knives and a bloody fingerprint left on a door frame no male DNA profiles were found. That means the blood is likely that of the victims: JoAnn Tate, 35, Melissa, 7, and Renee, 4.

What it means for Lincolns actual innocence claim, when paired with tests in 2010 that gave him hope, is disputed.

Lincolns lawyers, from the Midwest Innocence Project, argue the DNA results contradict faulty science and misleading testimony that was key to sending him to prison three decades ago on a double life sentence.

It kind of blows their whole case apart, said legal director Laura OSullivan, contending a jury would not convict if presented with the case anew.

But Circuit Attorney Jennifer Joyces office has argued the conviction never rested on science that eyewitness testimony of the two girls sealed Lincolns fate. Through a spokesperson for the office, prosecutors declined to speak about the case for this article.

St. Louis Circuit Court Judge Robin Vannoy has scheduled a three-day hearing in September to consider both sides. It will be the culmination of a seven-year battle under a state law that allows for post-conviction DNA testing in certain instances, and will be key to whether Lincolns convictions are overturned.

Lincolns case was one of six Joyce chose for testing in 2003 from among 1,400 pre-DNA-era convictions. But her office reversed course after learning more about the evidence in his case.

The Midwest Innocence Project got involved in 2005 to push for the DNA tests, setting the stage for the current battle.

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New DNA tests in brutal 1982 slaying in St. Louis set the stage for a decisive hearing