Daily Archives: September 24, 2015

Deoxyribonucleic acid (DNA) in a living cell contains the master blueprint for the production of proteins and for the replication of itself. It is the repository for the hereditary information. DNA accomplishes protein production by first providing a pattern for the production of mRNA, a process called transcription. The RNA then contains the information from the DNA to manufacture a protein, a process called translation. Some proteins are structural, but some are control proteins called enzymes. These enzymes are employed in the production of proteins, even copies of themselves, so enzymes are used to make other enzymes. Each protein, including enzymes, is made according to a pattern of nucleotides along a segment of the DNA called a "gene". A single living cell contains thousands of enzymes.

Another way to organized these ideas is in terms of the "central dogma" of molecular biology.

Though a useful organizing structure, the "central dogma" has numerous exceptions. For example, retroviruses use "reverse transcription" to construct DNA from RNA. In general, not every gene gets expressed all the way to the construction of proteins. Some RNAs have other tasks to do, such as the ribosomal RNA and other specifically tasked RNAs with specific tasks in the cell.

Biochemical concepts

Chemistry concepts

See the rest here:
DNA - Georgia State University

Remains of unidentified soldiers who died aboard battleship Oklahoma during 1941 Pearl Harbor attack are being reexamined and subjected to DNA testing in order to confirm their identities; severe damage done to bodies on Oklahoma, one of two ships in battle damaged beyond repair, has made identification process difficult. MORE

Hannah Landenmark study in journal PLoS Biology calculates global biodiversity using new metric of amount of DNA found on Earth; study reports Earth contains around 50 trillion trillion trillion DNA base pairs. MORE

David Rosenberg, who was given up for adoption by his mother Margaret Erle Katz in 1962, relocated her with help of a DNA testing kit and the Internet, only to have less than a month with her before he succumbed to thyroid cancer; growing number of adoptees are locating birth parents using similar tools. MORE

Atlanta jury awards more than $2 million to Atlas Logistics Group Retail Services workers who were required to submit to DNA samples in effort to identify out who had been defecating in warehouse. MORE

DNA matching Richard W Matt and David Sweat, murderers who escaped from Clinton Correctional Facility in upstate New York, is found in cabin 15 miles from prison; Matt and Sweat were discovered missing from prison on June 6. MORE

DNA evidence extracted from elephant dung, tissue and hair could help researchers to identify origins of illegal ivory and target poachers. MORE

Researchers have created fuller picture of how Ebola virus spread and evolved during 2014 outbreak by sequencing genomes of viruses from over 400 patients in Sierra Leone, Guinea and Liberia. MORE

Study published in journal Nature finds that Kennewick Man, 8,500-year-old skeleton that was discovered in Washington state riverbed, has no European DNA, and that he was likely most closely related to Native Americans; remains became subject of controversy as various groups attempted to claim them. MORE

London-based skincare store GeneU uses DNA testing to match treatments to each customer. MORE

Two studies in journal Nature present largest examinations ever done of ancient European DNA, extracted from 170 skeletons found in countries from Spain to Russia; both studies show Europeans descend from three groups who entered area at different stages in history. MORE

Atlanta judge rules that Atlanta warehouse owner Atlas Logistics Group Retail Services violated Genetic Information Nondiscrimination Act when it tested DNA of two men to determine if they had been leaving piles of feces around workplace; decision in unusual case shows scope of law goes beyond its original intent. MORE

Mat Johnson Lives essay describes taking DNA test in order to clear up question of how black he really is, and having one done for his mother as well; notes that there are issues of identity that cannot be resolved by finding out details of one's racial heritage. MORE

Researchers are making progress in using immunotherapy to fight cancer, or using DNA mutations inherent in immune system to beat cancer at its own game; questions remain, however, as to why treatments work better against some cancers than others and why some patients do not respond. MORE

National Institute of Standards and Technology announces new reference standards that could be used to ensure accuracy of DNA testing; marks important step towards new era in the use of genetic medicine. MORE

Profile of Dr Jennifer A Doudna, biochemist at University of California, Berkeley, who is fighting for control of potentially highly profitable intellectual property rights to what is known as the Crispr-Cas9 genome editing technique; Doudna, who helped discover the process, is also actively working to deepen scientific community's understanding of bioethics concerns that have arisen from the revelation of this new way to alter DNA. MORE

Dr Love Dalen study published online in Current Biology reports that researchers have sequenced DNA of woolly mammoth and have determined that species most likely died out on an isolated island from inbreeding. MORE

Law enforcement authorities arrest Joseph Giardala at Los Angeles International Airport and return him to New York to face charges after DNA evidence links him to 1995 rape case in West Village; case is latest effort by Manhattan District Attorney Cyrus Vance Jr to use DNA to solve cold cases. MORE

Chinese researchers try and fail to permanently alter DNA in human embryos; widely-predicted failure follows outcry from scientific community, which had called for halt to research until it could be proved safe and until ethical debate could proceed; researchers were attempting to alter DNA in manner that would be passed on to future generations. MORE

DNA-matching web sites have brought to forefront stories of babies illegally sold by Gertrude Pitkanen of Butte, Mont, to adoptive couples through the 1950s; baby-sellers like Pitkanen, midwife who also performed illegal and sometimes fatal abortions, are part of mid-20th century American subculture; so-called Gertie's Babies, who have found relatives through sites, say they are unique as they never found living biological parents due to how securely secrets were kept. MORE

DNA study published in online digital library bioRxiv reports that geneticists in Great Britain have found Armenians are mix of ancient populations that existed from 3000 to 2000 BC; period confirms date given by fifth century historian Movses Khorenatsi for founding of Armenia. MORE

Scientific community is engaged in debate about whether majority of any given genome's DNA actually serves purpose; recent research has caused some to question idea, and debate is in many ways latest skirmish in intellectual battle that has been going on for 200 years. MORE

Study in journal Science concludes that wheat has existed in Great Britain for 8,000 years, according to DNA evidence, suggesting that it made its way from Neolithic farmers of Southern Europe to Mesolithic hunter-gatherers of Britain. MORE

Scientists are developing tools that allow investigators to create facial image of suspect using DNA found at crime scene; process, known as forensic DNA phenotyping, has raised concerns among some who question technology's accuracy or warn that it could increase racial profiling or lead to privacy violations. MORE

Study in journal Current Biology shows that mice embryos injected with bits of human DNA grow brains 12 percent larger than embryos injected with chimpanzee genes, demonstrating role that gene sequence HARE5 plays in human brain development. MORE

Scientists are finding that they can confirm presence of animal species in a particular location and track their movements by collecting animal's DNA that was shed in environment; DNA samples may persist in area for weeks, allowing researchers to detect invasive and resurgent species, animal diversity, and, perhaps eventually, to measure animal populations. MORE

Pres Obama plans to request hundreds of millions of dollars to fund research into medical treatments attuned to specific patients' DNA and other characteristics; some experts consider so-called 'personalized medicine' or 'individualized medicine' to be forefront of field. MORE

California's First District Court of Appeal strikes down state law requiring collection of DNA from anyone arrested on suspicion of committing a felony, citing state Constitution's ban on unreasonable search and seizure. MORE

Nobel laureate James D Watson, a pioneer in DNA science, will auction his prize medal and donate much of proceeds to educational institutions; move is part of Watson's effort to redeem himself after making offensive remarks about race in 2007 that tarnished his reputation. MORE

DNA analysis of bite marks on harbor porpoises shows that gray seals are often responsible for wounds. MORE

Research shows that obtaining DNA swab from fang mark of snake bite can accurately identify type of snake, helping medical professionals to administer correct antivenin. MORE

Office of Chief Medical Examiner holds New York City Missing Persons Day to help identify the roughly 1,200 bodies they have received since about 1990 that they have been unable to identify; relatives gather to offer DNA samples, which will be used to create a corresponding forensic number that is then crosschecked against genetic information in a city database and others maintained by municipalities across the country. MORE

Study in journal Nature reports that scientists have reconstructed genome of man who lived 45,000 years ago, by far the oldest genetic record ever obtained from modern humans; research provides new clues to expansion of modern humans from Africa into Europe and Asia, as well as strong evidence that early humans interbred with Neanderthals. MORE

Experts working to identify the victims of Malaysia Airlines Flight 17 say they have positively identified 173 individuals from DNA samples. MORE

Food and Drug Administration approves first screening test for colon cancer that uses patients DNA to help spot potentially deadly tumors and growths. MORE

Italian police link Massimo Giuseppe Bossetti to 2011 murder of 13-year-old Yara Gambirasio after embarking on country's largest DNA dragnet, taking genetic samples from nearly 22,000 people; DNA testing also unexpectedly revealed that Bossetti was the illegitimate son of a man who had died in 1999, setting off debate over risks of privacy violations in criminal investigations involving DNA searches. MORE

Dr Bryan Sykes study in Proceedings of the Royal Society B performs first rigorous genetic analysis of three dozen hair samples that collectors claim came from undiscovered living humanoids, such as the Yeti or Sasquatch; study reveals that hairs came from range of known creatures, from humans to dogs. MORE

New fertility treatment could avoid certain hereditary diseases by altering genetic makeup of egg, raising issues of whether or not such a process is ethical or even safe. MORE

Study published in journal Nature Communications reports that researchers are able to determine where strain of malaria originated by using DNA 'bar code' of 23 short snips from genes of parasites. MORE

Researchers at University of California, San Francisco, use DNA sequencing to pinpoint, within 48 hours, what had been causing 14-year-old Joshua Osborn's brain to swell for weeks; breakthrough holds great promise for diagnostics, but experts say it will be years before method is in widespread use; case is reported in the New England Journal of Medicine. MORE

Adam Liptak Sidebar column; South Carolina Supreme Court will decide whether to hear appeal of Billy Wayne Cope, who claims his confessions in 2001 rape and murder of his daughter were coerced; DNA tests identified a different man, James Sanders, as the perpetrator. MORE

Scientists at Scripps Research Institute create first living organism with artificial DNA, taking significant step toward altering the fundamental alphabet of life; accomplishment could lead to new antibiotics, vaccines and other products, though a lot more work needs to be done before this is practical; research, published online in journal Nature, is bound to raise safety concerns and questions about whether humans are playing God. MORE

Study in journal PLoS One reports that Harvard researchers generated hemihelix, helix that changes direction midway, while working with complex rubber band; unusual shape is variation on helix often associated with DNA strand. MORE

Op-Ed article by evolutionary geneticist Svante Paabo warns against using sequenced genomes of Neanderthals to re-create Neanderthal individuals; contends from an ethical perspective such an idea should be condemned, and argues that using stem cells to create cells and tissues in test tubes for research is far more ethically defensible and technically feasible. MORE

Scientists have revealed that unusual repeating DNA sequence occurring next to gene in common bacterium are part of sophisticated immune system used to fight viruses; molecular system, known as Crispr, may provide scientists with power to edit genome and make precise changes to DNA of humans, essentially rewriting code of life. MORE

Municipal administration in Naples, Italy, decides to take DNA samples of dog waste on the sidewalks so that they may track down owners who do not pick up after their dogs; cutting-edge campaign is attempt to address widespread urban problem. MORE

British scientists will grind up some of King Richard IIIs bones to try to sequence his genetic code, about a year and a half after discovery of his corpse. MORE

British scientists will grind up some of King Richard IIIs bones to try to sequence his genetic code, about a year and a half after discovery of his corpse. MORE

Anne Eisenberg Novelties column holds that as technology becomes more sophisticated, genomic sequencing will inevitably expand into the world of newborns, but the process has both medical and ethical implications. MORE

Two studies show how the legacy of Neanderthals endures 30,000 years after their extinction, finding Neanderthal genes in skin and hair that may have helped humans evolve; findings appear in journals Nature and Science. MORE

There are no additional abstracts to display.

Original post:
DNA - News - Science - The New York Times

DNA, or deoxyribonucleic acid, is like a blueprint of biological guidelines that a living organism must follow to exist and remain functional. RNA, or ribonucleic acid, helps carry out this blueprint's guidelines. Of the two, RNA is more versatile than DNA, capable of performing numerous, diverse tasks in an organism, but DNA is more stable and holds more complex information for longer periods of time.

DNA and RNA are nucleic acids. Nucleic acids are long biological macromolecules that consist of smaller molecules called nucleotides. In DNA and RNA, these nucleotides contain four nucleobases sometimes called nitrogenous bases or simply bases two purine and pyrimidine bases each.

DNA is found in the nucleus of a cell (nuclear DNA) and in mitochondria (mitochondrial DNA). It has two nucleotide strands which consist of its phosphate group, five-carbon sugar (the stable 2-deoxyribose), and four nitrogen-containing nucleobases: adenine, thymine, cytosine, and guanine.

During transcription, RNA, a single-stranded, linear molecule, is formed. It is complementary to DNA, helping to carry out the tasks that DNA lists for it to do. Like DNA, RNA is composed of its phosphate group, five-carbon sugar (the less stable ribose), and four nitrogen-containing nucleobases: adenine, uracil (not thymine), guanine, and cytosine.

In both molecules, the nucleobases are attached to their sugar-phosphate backbone. Each nucleobase on a nucleotide strand of DNA attaches to its partner nucleobase on a second strand: adenine links to thymine, and cytosine links to guanine. This linking causes DNA's two strands to twist and wind around each other, forming a variety of shapes, such as the famous double helix (DNA's "relaxed" form), circles, and supercoils.

In RNA, adenine and uracil (not thymine) link together, while cytosine still links to guanine. As a single stranded molecule, RNA folds in on itself to link up its nucleobases, though not all become partnered. These subsequent three-dimensional shapes, the most common of which is the hairpin loop, help determine what role the RNA molecule is to play as messenger RNA (mRNA), transfer RNA (tRNA), or ribosomal RNA (rRNA).

DNA provides living organisms with guidelinesgenetic information in chromosomal DNAthat help determine the nature of an organism's biology, how it will look and function, based on information passed down from former generations through reproduction. The slow, steady changes found in DNA over time, known as mutations, which can be destructive, neutral, or beneficial to an organism, are at the core of the theory of evolution.

Genes are found in small segments of long DNA strands; humans have around 19,000 genes. The detailed instructions found in genesdetermined by how nucleobases in DNA are orderedare responsible for both the big and small differences between different living organisms and even among similar living organisms. The genetic information in DNA is what makes plants look like plants, dogs look like dogs, and humans look like humans; it is also what prevents different species from producing offspring (their DNA will not match up to form new, healthy life). Genetic DNA is what causes some people to have curly, black hair and others to have straight, blond hair, and what makes identical twins look so similar. (See also Genotype vs Phenotype.)

RNA has several different functions that, though all interconnected, vary slightly depending on the type. There are three main types of RNA:

DNA's genes are expressed, or manifested, through the proteins that its nucleotides produce with the help of RNA. Traits (phenotypes) come from which proteins are made and which are switched on or off. The information found in DNA determines which traits are to be created, activated, or deactivated, while the various forms of RNA do the work.

One hypothesis suggests that RNA existed before DNA and that DNA was a mutation of RNA. The video below discusses this hypothesis in greater depth.

Here is the original post:
DNA vs RNA - Difference and Comparison | Diffen

An Interactive Animated Nonlinear Tutorial by Eric Martz Adapted for using Jmol instead of Chime, by Angel Herrez Part of Biomodel website by Angel Herrez, Univ. de Alcal (Spain)

Disponible tambin en espaol. Tambm disponvel em portugus. Auch verfgbar auf Deutsch. Disponible aussi en franais.

This version works in any Java-compatible browser. Java Virtual Machine must be installed (JVM, included with some operating systems or available in Sun's Java website). More tutorials on DNA and proteins, in English, Spanish, etc., are indexed at molvisindex.org.

If you prefer using Chime for molecular models, the page using it is still available, with equivalent content and functionality.

This tutorial is designed to complement Biology or Biochemistry and Molecular Biology books, so it is not by itself a complete introduction to DNA structure. Please, check the original source for more recent versions. You can also read the version history.

You can request a copy of this tutorial for off-line use; once you have your own copy on your computer's hard disk, you can use it without an Internet connection (and it will run faster).

Methods, Acknowledgements, and References.

Do you know there are more tutorials at MolviZ.Org? Feedback/Requests to or .

More about Jmol: Jmol home page.

The use of this work is subjected to the conditions stated on the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License (details)

This DNA Tutorial is being used in the Biomedical Sciences Curriculum developed by Project Lead The Way, Inc., a not-for-profit corporation that provides curriculum at no charge to high schools and middle schools located in the United States.

This DNA Tutorial (English and Spanish versions) has been included in BioMolecular Explorer 3D, version 2, a website+CD-ROM designed to give high school biology teachers easy access to interactive 3D structures of biologically significant molecules.

This DNA Tutorial (English and Spanish versions) has been included in the live bootable DVD Xplora Knoppix, by Xplora - The European Science Education Gateway.

Read the original:
DNA Structure - Contents page

Despite what you may have seen in some textbooks, DNA is not built like a twisted ladder. The helix, or spiral, is an inherent feature of the DNA molecule. Notice, for instance, that in the picture below, that the groove on the left side of the picture is much larger than the right side. This is because the paired bases in the center meet each other at an angle.

DNA is a very large molecule; the image here shows only a tiny fraction of the typical molecule. If an entire molecule of DNA from the virus "bacteriophage lambda" were shown at this scale, the image would be 970 meters high. For the bacterium Escherichia coli, the image would be 80 kilometers long. And for a typical piece of DNA from a eukaryote cell, the image would stretch for 1600 kilometers, about as far as it is from Dallas to Washington, D. C.! Obviously such a large molecule is not fully stretched out inside the cell, but is wound around proteins called histones which protect the DNA.

Visit link:
DNA - University of California Museum of Paleontology

rotten > Library > Medicine > DNA How did life first get started on this planet? And why does it suck so much? The answer is found in DNA.

DNA was discovered in 1869, but at the time, no one really knew what it was or whether it was important. Scientists knew that it was a complicated molecule found inside the cells of living things, and they suspected it had something to do with heredity.

In 1944, quantum physicist Erwin Schrodinger (of "Schrodinger's Cat" fame) published a collection of lectures titled What is Life? Schrodinger postulated that all life was somehow designed according a pre-set script that could found among the molecules of the body.

Following on his discoveries in the study of subatomic systems, Schrodinger believed that information about the structure of a life form was physically encoded into the life form at a very small scale, and that the code was inherited by each generation from the previous. Schrodinger challenged his contemporaries in the life sciences to find that code.

In the 1950s, two young scientists named James Watson and Francis Crick discovered that the molecules of DNA were coiled up in the double helix formation. A couple of years later, an experiment using bacteria proved that DNA was the medium for transferring hereditary -- also called genetic -- information.

By the time you finish reading this next section, you might well think DNA stands for "Do Not Ask," but it's actually an abbreviation for deoxyribonucleic acid. DNA is a string-shaped molecule arranged as two strands spiraling around each other, connected through the middle by hydrogen atoms. The shape is known as a "double helix."

The DNA molecule is twined very tightly, so that a large number of atoms fit into a very small space. Each strand of DNA contains a number of smaller molecule-like clusters of atoms, known as nucleotides. There are four nucleotides, each usually represented by a letter -- A, T, C, or G.

From here out, everything you read is going to be pretty grossly oversimplified. The nucleotide letters are arranged into three-letter "words" known as codons. There are 64 codons, or 64 possible combinations of the four nucleotides. (There are also 64 hexagrams in the I-Ching, which may or may not be a coincidence.) Each codon is sort of like a command in computer coding -- an instruction on how to do something.

Each set of instructions is framed by a "start" and "stop" codon. These markers are like a set of parentheses. Inside the parentheses, there is one specific set of instructions, which is almost always (Make a protein.) When a new set of parentheses begin, a new instruction has been launched, such as (Make a different protein.)

These instructions are carried out by RNA, or ribonucleic acid. Here's how it works: A molecule called an enzyme bonds with DNA, and the resulting chemical reaction creates RNA. When you unstick the RNA from the DNA, the RNA carries an impression of the DNA, called a transcription.

The RNA then drops into a simmering stew of amino acids, which are the carbon-based raw materials of life. The amino acids interact chemically with the RNA segment to make proteins, in a type dictated by the information copied from the parenthetical DNA segment. Like the gears and springs in a pocket watch, proteins are the fundamental machines that do the work of life within a cell.

If your eyes are glazing over right about now, don't feel bad. It's insanely complicated. Here's an absurdly oversimplified (but surprisingly reasonable) way to think about it: DNA is like a long string of connected Legos, and RNA is like Play-Doh.

The Play-Doh (RNA) presses onto the string of Legos (DNA), which leaves an indentation in the Play-Doh. The Play-Doh gets tacky and falls away from the Legos. The now-stiff Play-Doh drops into a pile of loose Legos (amino acids). As they bang around together, appropriately shaped Legos snap into the impressions left in the Play-Doh to make a new Lego construct (a protein).

The type and number of proteins in a cell determine whether the cell is a bone cell, a blood cell, a brain cell, or a spleen cell. By following some specific combination of codons in a segment of DNA, RNA manufactures all the parts that go into a cell, and by following the entire recipe book (decoding the entire strand of DNA in the correct order and with the proper raw materials), you can incubate an entire person... or cat, dog, mouse, aardvark, bacterium, virus, fungus, sunflower or dragonfly.

So this bizarre little super-complicated molecule holds basic recipe book on how to build a human being in about eleventy million trillion easy steps. How did this come to be?

We know that the origins of DNA are the origins of life on this planet. Unfortunately knowing that and knowing the actual origins of DNA are two different things.

Experiments have demonstrated that the combination of base chemicals and environmental conditions on primitive Earth -- including lava, electrical storms, carbon and water -- were conducive to the formation of complex organic molecules. Some organic molecules formed on Earth; others may have been dropped here by passing comets or meteors. It's not quite clear how, but all these factors appear to have come together to form RNA first, then RNA eventually became more complex and developed into DNA.

There isn't really any one view about how this happened, but the earliest forms of life derived from these first building blocks. Well, according to most views, anyway. From these simple building blocks, more complex forms of life evolved through the process of mutation. Because the process described above are extremely complex and involve millions of small chemical changes, there are numerous opportunities for something to go wrong between the Legos and the Play-Doh.

Although DNA can repair itself to a certain extent, some errors persist and are inherited by the next generation of the life form in question. Over the course of a great deal of time, this eventually led to the development of opposable thumbs, tonsils and third nipples.

Although the stuff was unimaginable just 200 years ago, DNA is now a part of everyday life. Because each person inherits a unique genetic sequence, DNA has revolutionized criminal investigations by offering a not-quite infallible method of identifying suspects from the blood, semen, spit and hair they leave behind. DNA testing can be used to establish paternity within an inconsequential margin of error.

In medicine, DNA grows more prominent every day. Although the genetic code still contains mysteries, scientists have managed to unlock genetic markers for various diseases. Some diseases are directly caused by faulty DNA. Gene therapy -- in which healthy DNA is spliced onto damaged DNA -- is still in its early stages. Gene therapy shows promise in principle, but its track record in clinical trials to date isn't stellar.

Then there's genetic engineering. We may not fully understand how DNA works, or where it came from, or exactly precisely how all those little codons work, but in typical human form, we have already figured out how to monkey with them.

Genetic engineering is rampant in the U.S. food industry, including tomatoes, beets, wheat and corn. On the bright side, GE has made foods more resistant to spoilage, more easily processed, or more easily cooked. GE hybrids, whether plants or animals, are known as transgenic organisms.

In order to accomplish this goal, genetic engineers do some questionable things, like splicing fish genes onto strawberries to keep them from freezing, or splicing human genes into chickens to make them grow larger more rapidly. Some early experimentation has been done splicing human DNA into pigs in order to grow pigs with organs that can then be transplanted into humans. (Would eating bacon from these pigs constitute cannibalism?)

Much of this gene splicing is done by introducing an engineered virus into the host organism. By their nature, viruses tinker with the DNA of host cells, so the strategy has a certain logic behind it. On the other hand, if you think there's something inherently alarming about creating viruses and introducing them into animals in order to create bizarre new interspecies hybrids, you're not alone.

The ultimate frontier -- tampering with the DNA of human beings -- is just around the corner. Rumors of human cloning persist, but no proven clones have surfaced yet.

There are two predominant reasons to tamper with human DNA -- to improve the health of a living human, or to breed children with specific traits, presumably superior ones. Experiments in the former area have been hampered because patients have an annoying tendency to die. It turns out that inserting genetically engineered viruses into people and animals can be bad for their health. Who would have thought it?

Experiments in the latter field, sometimes known as eugenics, are equally troublesome. Although trials with animals have produced super-smart mice and sheep whose breast milk contains insulin, it's still relatively taboo to talk about manufacturing smart, beautiful children with an insatiable appetite for world domination.

In the old days, eugenics had to be accomplished through the cumbersome task of selective breeding, but modern geneticists are increasingly able to manipulate DNA directly to enhance qualities such as strength, resistance to disease and intelligence. Although Adolf Hitler gave eugenics a bad name during the 1940s, scientists are still plugging away to promote the practice.

Although current efforts are mostly limited to examining ways to diagnose and treat genetically transmitted diseases like cystic fibrosis and cancer, you know it won't be long before we're all battling for our lives against a generation of supermen whose genes for morality were accidentally excised by an overeager scientist trying to prevent warts.

Naturally, we won't be able to beat them. You can only hope that the technology to create these superbabies won't exist during our lifetimes... which would be fairly pointless since the technology pretty much exists already, held in check by only a rapidly fraying string of ethical posturing. After all, the last time you stopped at McDonald's, you ate a tomato with fish genes in it. Pretty much anything goes after that.

O brave new world!

More here:
DNA - Rotten.com

DNA Structure and Function

Background History:

Mitosis in onion root tip DNA stands for deoxyribonucleic acid. DNA is pretty unusual in that it is about the only common molecule capable of directing its own synthesis.

The processes of mitosis and meiosis were discovered in the 1870s and 1890s. It was observed that, as cells divided, chromosomes moved around in a cell, and people began to wonder what their function was. It was determined that chromosomes were made of protein and DNA, about which people knew almost nothing. People began to suspect that chromosomes had something to do with genetics, but couldnt explain what/how. When enough evidence was accumulated to confirm that chromosomes did, indeed, have something to do with genetics, most people thought that in some way the protein in the chromosomes served as the genetic material. People knew that DNA was also in the chromosomes, but because its structure was unknown and people didnt know much about it, few people thought it was the genetic material.

Griffiths Experiment In 1928, Frederick Griffith performed an experiment using pneumonia bacteria and mice. This was one of the first experiments that hinted that DNA was the genetic code material. Click on the mouse button to study his experiment. He used two strains of Streptococcus pneumoniae: a smooth strain which has a polysaccharide coating around it that makes it look smooth when viewed with a microscope, and a rough strain which doesnt have the coating, thus looks rough under the microscope. When he injected live S strain into mice, the mice contracted pneumonia and died. When he injected live R strain, a strain which typically does not cause illness, into mice, as predicted they did not get sick, but lived. Thinking that perhaps the polysaccharide coating on the bacteria somehow caused the illness and knowing that polysaccharides are not affected by heat, Griffith then used heat to kill some of the S strain bacteria and injected those dead bacteria into mice. This failed to infect/kill the mice, indicating that the polysaccharide coating was not what caused the disease, but rather, something within the living cell. Since Griffith had used heat to kill the bacteria and heat denatures protein, he next hypothesized that perhaps some protein within the living cells, that was denatured by the heat, caused the disease. He then injected another group of mice with a mixture of heat-killed S and live R, and the mice died! When he did a necropsy on the dead mice, he isolated live S strain bacteria from the corpses. Griffith concluded that the live R strain bacteria must have absorbed genetic material from the dead S strain bacteria, and since heat denatures protein, the protein in the bacterial chromosomes was not the genetic material. This evidence pointed to DNA as being the genetic material. Transformation is the process whereby one strain of a bacterium absorbs genetic material from another strain of bacteria and turns into the type of bacterium whose genetic material it absorbed. Because DNA was so poorly understood, scientists remained skeptical up through the 1940s.

Hershey & Chases Experiment In 1952, Alfred Hershey and Martha Chase did an experiment which is so significant, it has been nicknamed the Hershey-Chase Experiment. Click on the virus button to study their experiment. At that time, people knew that viruses were composed of DNA (or RNA) inside a protein coat/shell called a capsid. It was also known that viruses replicate by taking over the host cells metabolic functions to make more virus. We are used to thinking and talking about viruses which invade our bodies and make us sick, but there are other, different kinds of viruses that infect other kinds of animals, still other viruses which infect plants, and even some viruses that infect bacteria. A virus which infects a bacterium is called a bacteriophage because the host bacterium cell is killed as the new virus particles leave the bacterial cell. In order to do all this, the virus must inject whatever is the viral genetic code into the host cell. Thus, people realized that the viral genetic code material had to be either its DNA or its protein capsid. Hershey and Chase sought an answer to the question, Is it the viral DNA or viral protein coat (capsid) that is the viral genetic code material which gets injected into a host bacterium cell? To try to answer this question, Hershey and Chase performed an experiment using a bacterium named Escherichia coli, or E.coli for short (named after a scientist whose last name was Escher) and a virus called T2 that is a bacteriophage that infects E.coli. Isolated T2, like other viruses, is just a crystal of DNA and protein, so it must live inside E.coli in order to make more virus like itself. When the new T2 viruses are ready to leave the host E.coli cell (and go infect others), they burst the E.coli cell open, killing it (hence the name bacteriophage). The results that Hershey and Chase obtained indicated that the viral DNA, not the protein, is its genetic code material.

Hershey and Chase used radioactive chemicals to distinguish between (label) the protein capsid and the DNA in T2 virus so they could tell which of those molecules entered the E.coli cells. Since some amino acids contain sulfur in their side chains, if T2 is grown in E.coli with a source of radioactive sulfur, the sulfur will be incorporated into the T2 protein coat making it radioactive. Since DNA has lots of phosphorus in its phosphate (PO4) groups, if T2 is grown in E.coli with a source of radioactive phosphorus, the phosphorus will be incorporated into the viral DNA, making that radioactive. Hershey and Chase grew two batches of T2 and E.coli: one with radioactive sulfur and one with radioactive phosphorus to get batches of T2 labeled with either radioactive S or radioactive P. Then, these radioactive T2 were placed in separate, new batches of E.coli, but were left there only 10 minutes. This was to give the T2 time to inject their genetic material into the bacteria, but not reproduce. In the next step, still in separate batches, the mixtures were agitated in a kitchen blender to knock loose any viral parts not inside the E.coli but perhaps stuck on the outer surface. Hopefully, this would differentiate between the protein and DNA portions of the virus. Then, each mixture was spun in a centrifuge to separate the heavy bacteria (with any viral parts that had gone into them) from the liquid solution they were in (including any viral parts that had not entered the bacteria). The centrifuge causes the heavier bacteria to be pulled to the bottom of the tube where they form a pellet, while the light-weight viral left-overs stay suspended in the liquid portion called the supernatant. In the subsequent step, the pellet and supernatant from each tube were separated and tested for the presence of radioactivity. Radioactive sufur was found in the supernatant, indicating that the viral protein did not go into the bacteria. Radioactive phosphorus was found in the bacterial pellet, indicating that viral DNA did go into the bacteria.

Based on these results, Hershey and Chase concluded that DNA must be the genetic code material, not protein as many poeple believed. When their experiment was published and people finally acknowledged that DNA was the genetic material, there was a lot of competition to be the first to discover its chemical structure.

Discovery of the Structure of DNA:

What was known is that DNA contains a nitrogenous base. There are two kinds of these, which include:

Nucleoside Nucleotide Each nitrogenous base is connected to a molecule of ribose sugar (1 oxygen in DNA) to form a nucleoside like the adenosine in ATP.

Each nucleoside is joined to a PO4 (phosphate group, ) to form a nucleotide like adenosine monophosphate (which can be turned into ATP by adding phosphate groups).

Deoxy Nucleotide People also knew that nucleotides were somehow linked by dehydration synthesis to form DNA, but the exact structure/arrangement was unknown.

In the early 1950s, Rosalind Franklin, an Englishwoman, was doing research which involved bouncing x-rays off crystals of various substances (a process which is called x-ray crystallography or x-ray crystal diffraction), including DNA, then exposing photographic film to the x-rays. She was studying the scatter patterns made by the x-rays bouncing off the crystals of various substances (Unfortunately, she died of cancer soon afterwards, or she might have been more famous). Other people like Linus Pauling were also attempting to figure out the structure of DNA.

Structure of DNA James Watson, a young American scientist was in England working with Francis Crick, another young researcher. Someone showed them Franklins 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. Based on Franklins data, in 1953, Watson and Crick published a paper in which they proposed and described an hypothetical structure for DNA. Subsequent research by many other people has since upheld their hypothesis, and based on subsequent examination of Franklins lab notes and calculations, she was probably within a couple days of coming to the same conclusion when their paper was published. For their discovery, Watson and Crick received the Nobel prize in 1962. In the intervening time, Rosalind Franklin had died in 1958 of ovarian cancer, probably due in large part to her work with x-rays. Since the Nobel prize is not awarded posthumously, people have often wondered if the Nobel committee would have included Franklin if she had still been alive.

Double Helix DNA Replication DNA is a double helix. The outer edges are formed of alternating ribose sugar molecules and phosphate groups. The two strands go in opposite directions (1 up and 1 down). The nitrogenous bases are inside like rungs on a ladder. Adenine on one side pairs with thymine (uracil in RNA) on the other by hydrogen bonding, and cytosine pairs with guanine. Note that the C-G pair has three hydrogen bonds while the A-T pair has only two, which keeps them from pairing wrong. This dictates side-to-side pairing, but says nothing about the order along the molecule. Watson and Crick said this variability along the molecule can account for the variety in the genetic code. Their model also accounts for how DNA can replicate itself. They said the molecule unzips and new matching bases are added in to create two new molecules. They called this semiconservative replication because each new molecule has one old and one new strand of DNA.

DNA mRNA tRNA &rarr Protein:

Here is a list of the mRNA codons and the corresponding amino acids for which they code.

B a s e

B a s e

Transcription and Translation Practice

Here is a DNA gene for some fictitious protein. Transcribe the DNA code to RNA code, then translate the RNA code to an amino acid sequence. It is set up to only accept a 3-letter code, so use the codes sta for START and sto for STOP.

Mutations and Viruses:

Mutations can be caused by a change in the sequence of the nucleotides. Some mutations have more effect than others, depending on where in the code they are and how important that area is to the code. While mutations in some areas of some genes have little effect, sickle cell anemia is caused by a mutation in only one nucleotide. This changes the codon at that location to code for a different amino acid, and that, in turn, significantly changes the shape of the hemoglobin molecules in that persons blood.

When some viruses (especially Herpes viruses, including Chicken Pox and cold sores) infect us, they insert their DNA into our cells DNA, and stay resident in our cells for the rest of our lives. These can potentially become active again either making a person sick again (like Shingles in a person who has had Chicken Pox) or just being shed from a persons body (to infect others) without obvious symptoms of illness (like Mononucleosis). Some kinds of cancer may be caused this way. For example, there is some pretty strong evidence linking genital warts (human papillomavirus, HPV) and cervical cancer.

The AIDS virus does things backwards. This virus contains RNA rather than DNA, yet when it gets into someones cells, it can do reverse transcription and code from its RNA to make DNA which, then, can code to make more virus.

Genetic Engineering Is It Good or Bad?

We now have the knowledge and ability to transfer genes from one organism to another, which seems to have some benefits associated with it, but may also have many yet-to-be-discovered problems associated with it. Because this is all so new, not enough time has elapsed to allow scientists to study/look for any possible long-term effects of genetically-modified organisms (GMOs).

For more information on genetically-modified foods, see Dr.Fankhausers Web page on that topic.

References:

Berkow, Robert, ed. 1999. The Merck Manual. 17th ed. Merck, Sharp & Dohme, Rahway, NJ.

Borror, Donald J. 1960. Dictionary of Root Words and Combining Forms. Mayfield Publ. Co.

Campbell, Neil A., Lawrence G. Mitchell, Jane B. Reece. 1999. Biology, 5th Ed. Benjamin/Cummings Publ. Co., Inc. Menlo Park, CA. (plus earlier editions)

Campbell, Neil A., Lawrence G. Mitchell, Jane B. Reece. 1999. Biology: Concepts and Connections, 3rd Ed. Benjamin/Cummings Publ. Co., Inc. Menlo Park, CA. (plus earlier editions)

Marchuk, William N. 1992. A Life Science Lexicon. Wm. C. Brown Publishers, Dubuque, IA.

There are many Web pages with information relating to the Watson-Crick-Franklin-Wilkins story. Here is a small sample of the many that were found via a search:

Visit link:
DNA Structure and Function