Monthly Archives: February 2014

Like the one ring of power in Tolkien's "Lord of the Rings," deoxyribonucleic acid (DNA) is the master molecule of every cell. It contains vital information that gets passed on to each successive generation. It coordinates the making of itself as well as other molecules (proteins). If it is changed slightly, serious consequences may result. If it is destroyed beyond repair, the cell dies.

Changes in the DNA of cells in multicellular organisms produce variations in the characteristics of a species. Over long periods of time, natural selection acts on these variations to evolve or change the species.

The presence or absence of DNA evidence at a crime scene could mean the difference between a guilty verdict and an acquittal. DNA is so important that the United States government has spent enormous amounts of money to unravel the sequence of DNA in the human genome in hopes of understanding and finding cures for many genetic diseases. Finally, from the DNA of one cell, we can clone an animal, a plant or perhaps even a human being.

But what is DNA? Where is it found? What makes it so special? How does it work? In this article, we will look deep into the structure of DNA and explain how it makes itself and how it determines all of your traits. First, let's look at how DNA was discovered.

DNA is one of a class of molecules called nucleic acids. Nucleic acids were originally discovered in 1868 by Friedrich Meischer, a Swiss biologist, who isolated DNA from pus cells on bandages. Although Meischer suspected that nucleic acids might contain genetic information, he could not confirm it.

In 1943, Oswald Avery and colleagues at Rockefeller University showed that DNA taken from a bacterium, Streptococcus pneumonia, could make non-infectious bacteria become infectious. These results indicated that DNA was the information-containing molecule in the cell. The information role of DNA was further supported in 1952 when Alfred Hershey and Martha Chase demonstrated that to make new viruses, a bacteriophage virus injected DNA, not protein, into the host cell (see How Viruses Work for more information).

So scientists had theorized about the informational role of DNA for a long time, but nobody knew how this information was encoded and transmitted. Many scientists guessed that the structure of the molecule was important to this process. In 1953, James D. Watson and Francis Crick discovered the structure of DNA at Cambridge University. The story was described in James Watson's book "The Double Helix" and brought to the screen in the movie, "The Race for the Double Helix." Basically, Watson and Crick used molecular modeling techniques and data from other investigators (including Maurice Wilkins, Rosalind Franklin, Erwin Chargaff and Linus Pauling) to solve the structure of DNA. Watson, Crick and Wilkins received the Nobel Prize in Medicine for the discovery of DNA's structure (Franklin, who was Wilkins' collaborator and provided a key piece of data that revealed the structure to Watson and Crick, died before the prize was awarded).

See the rest here:
HowStuffWorks "How DNA Works"

In This Issue:

What Is DNA?

Deoxyribonucleic acid (DNA) is a chemical found in the nucleus of cells and carries the "instructions" for the development and functioning of living organisms. It is often compared to a set of blueprints since it contains the instructions needed to build cells. These instructions are divided into segments along a strand of DNA and are called genes. Genes are a DNA sequence that code for the production of a protein and control hereditary characteristics such as eye color or personality behaviors. Proteins determine the type and function of a cell, so a cell knows whether it is a skin cell, a blood cell, a bone cell, etc, and how to perform its appropriate tasks. Other DNA sequences are responsible for structural purposes or are involved in the regulation and use of genetic information.

Structure of DNA

The structure of DNA can be compared to a ladder. It has an alternating chemical phosphate and sugar backbone, making the "sides" of the ladder. (Deoxyribose is the name of the sugar found in the backbone of DNA.) In between the two sides of this sugar-phosphate backbone are four nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G). (A grouping like this of a phosphate, a sugar, and a base makes up a subunit of DNA called a nucleotide.) These bases make up the "rungs" of the ladder, and are attached to the backbone where the deoxyribose (sugar) molecules are located.

The chemical bases are connected to each other by hydrogen bonds, but the bases can only connect to a specific base partner - adenine and thymine connect to each other and cytosine and guanine connect to each other. The arrangement of these bases is very important as this determines what the organism will be - a plant, an animal, or a fungus. This is called genetic coding. For example, one side of DNA could have the genetic code of AAATTTCCCGGGATC. Its complementary side would then have to be TTTAAAGGGCCCTAG.

Even though the shape of DNA is often described as a ladder, it is not a straight ladder. It is twisted to the right, making the shape of the DNA molecule a right-handed double helix. This shape allows for a large amount of genetic information to be "stuffed" into a very small space. In fact, if you lined up each molecule of DNA in one cell end to end, the strand would be six feet in length.

DNA Replicates Itself

Before a cell can divide and make a new cell, it must first duplicate its DNA. This process is called DNA replication. When it is time to replicate, the hydrogen bonds holding the base pairs together break, allowing the two DNA strands to unwind and separate. The specific base pairing provides a way for DNA to make exact copies of itself. Each half of the original DNA still has a base attached to its sugar-phosphate backbone. A new strand of DNA is made by an enzyme called DNA polymerase. It reads the original strand and matches complementary bases to the original strand. (The sugar-phosphate backbone comes with the new bases.) New strands attach to both sides of the original DNA, making two identical DNA double helices composed of one original and one new strand.

Please note that the above explanation of DNA replication is highly simplified. To see a more detailed, animated explanation of the structure of DNA and the replication process, click here.

See the rest here:
DNA: Fun facts - Home Science Tools

STORY HIGHLIGHTS

(CNN) -- Two Brooklyn men who have spent the last 21 years in prison for three murders that DNA evidence suggests they did not commit were released Thursday on consent of the Brooklyn district attorney.

Anthony Yarbough, 39, and Sharrif Wilson, 37, were arrested in June 1992 in the slaying Yarbough's 40-year-old mother, his 12-year-old sister and another 12-year-old girl in a Coney Island housing project.

"In this case, my office examined newly discovered scientific evidence that was not available at the time of the trial," Brooklyn District Attorney Kenneth P. Thompson said in statement to CNN. "My obligation under the law is to determine whether this new information, had it been known and presented at trial, would have been more likely than not to cause the trial jury to return a different verdict."

In 2013, new DNA evidence from under Yarbough's mother's fingernails matched sperm from the 1999 unsolved rape and murder of Migdalia Ruiz of Brooklyn, according to an investigation by the Medical Examiner's office.

Anthony Yarbough, left, and Sharrif Wilson were released Thursday on consent of the Brooklyn district attorney after DNA evidence suggests they did not commit the crimes they were convicted for.

Yarbough and Wilson were already incarcerated when the 1999 rape and murder occurred, according to Adam Perlmutter, Wilson's attorney.

"Based on this new evidence, I believe a jury would have been more likely to return a different verdict," Thompson said.

Zachary Margulis-Ohuma, Yarbough's attorney, is glad justice has finally been served.

"Anybody looking at this evidence with an open mind would see that there is no chance in the world that Tony murdered his mother and these two little girls," Margulis-Ohuma said.

Read more:
DNA evidence frees 2 Brooklyn men convicted in 1992 triple murder

Two Brooklyn men locked up for 21 years for a gruesome triple murder walked out of court free on Thursday after new DNA evidence led prosecutors to drop all charges against them.

It feels amazing, it feels amazing! Anthony Yarbough, 39, cried out as he strode out into the cold winter air for the first time since he and pal Sharrif Wilson, 37, were convicted of killing his mother, 12-year-old sister and the sisters friend in 1992.

This smells a lot better than Atticas mess hall, Yarbough said an hour later as he sat with a dozen family members at Juniors on Atlantic Avenue.

Anthony Yarbough enjoys his BLT.Photo: Dennisthephotog.com Dennis A. Clark

Yarbough stared hungrily at a BLT when a waiter set it before him, but politely waited until his aunt was served her dinner.

Wilsons release was delayed because of paperwork, but when he finally walked out of court he said, Im so happy I cant even speak.

But he did say his first meal would be pizza and added, I want to go get a new iPhone 5, catch up on the times a little bit.

The two men were convicted even though Yarbough called 911 once he discovered the stabbed bodies and even though both men were hanging out in the West Village at the time the medical examiner believed the murders took place, court papers state.

Last year, DNA evidence taken from under the fingernails of Yarboughs slain mom was matched to DNA found on a woman raped and killed in 1999 while Yarbough and Wilson were behind bars.

In light of the newly discovered evidence, the people move to dismiss the indictments, Brooklyn prosecutor Mark Hale said to huge cheers from the mens family.

Read the original here:
DNA clears men after 21 years in prison for familys murder

By Laurel Maloy, contributing author, Food Online

European research suggests DNA barcoding can greatly increase speed and accuracy in identifying the origin of contaminated food

DNA Barcoding is the new cutting edge technology with the ability to greatly improve the traceability of our food from grower to dining table. The goal is to be able to identify different species from a standardized section of the genome. According to the European Food Information Council and Food Research International, this breakthrough would significantly enhance the ability and speed of discovering the source of contaminated food products. It would also serve to streamline a cumbersome and labor-intensive process. But is it a viable and cost-effective solution?

This latest advancement in traceability is the combination of two widely utilized technologies. In the early 1970s, the very first barcode readers were put into use in grocery stores. Their purpose was to be able to better monitor pricing and inventory while reducing costs. Today virtually everyone knows what a UPC (Universal Product Code) is and has some idea of the information it contains. The other half of the equation is utilizing DNA (Deoxyribonucleic Acid). Since its advent in 1985, DNA testing and its evidentiary use has become routine. DNA, once considered cutting edge, is now used to discern a biological fingerprint with better than 99% accuracy and is deemed commonplace.

The success DNA barcoding will have in improving foods traceability depends first upon the availability of high quality DNA samples in national repositories. DNA databases for human samples have taken a great deal of time to compile. The same will be true for the vast number of DNA samples to be gathered for the massive amount of food flowing through the supply chain. DNA barcoding success will also depend upon the broad molecular variability between the ever-growing varieties of foods. This, in some instances, has proven to be problematic, particularly in the case of hybridized livestock and poultry.

The goal for DNA barcoding is to always utilize the smallest samples possible, comparing short genetic markers. There are actually no technical limitations to DNA barcoding at the raw material level. However, detractors argue that hybridization occurs at the cultivar level of plants, and thus, would require analysis of larger portions of the genome. This would be more time-consuming, as well as more costly.

Great strides are being made in DNA barcoding throughout Europe. The technology has been used to identify certain types of processed foods, such as fruit in yogurt and juices, tea, purees, and chocolates. However, it should be noted that the very act of processing foods can alter the DNA structure, making the application of DNA barcoding on processed commodities ineffective.

Nevertheless, when it comes to identifying animal and plant species, exclusive gene regions have been identified and approved. Using specialized markers, samples can be sequenced quickly and inexpensively, and are long enough to accurately identify the variations among species.

European researchers have concluded that the idea of using DNA barcoding as a universal tool for traceability has merit. Different regulatory authorities, i.e.: the FDA, USDA, and CDC may use it in different contexts; however, ultimately, this technology would be invaluable to traceability and accountability. There is, though, a whole lot of work to do before it shifts from idea to reality, just like UPC scanning and DNA evidence.

Want to publish your opinion? Contact us to become part of our Editorial Community.

Read more:
Is DNA Barcoding The Future Of Food Traceability?