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Deoxyribonucleic acid (DNA) is a molecule that encodes the genetic instructions used in the development and functioning of all known living organisms and many viruses. DNA is a nucleic acid; alongside proteins and carbohydrates, nucleic acids compose the three major macromolecules essential for all known forms of life. Most DNA molecules are double-stranded helices, consisting of two long biopolymers made of simpler units called nucleotideseach nucleotide is composed of a nucleobase (guanine, adenine, thymine, and cytosine), recorded using the letters G, A, T, and C, as well as a backbone made of alternating sugars (deoxyribose) and phosphate groups (related to phosphoric acid), with the nucleobases (G, A, T, C) attached to the sugars.

DNA is well-suited for biological information storage. The DNA backbone is resistant to cleavage, and both strands of the double-stranded structure store the same biological information. Biological information is replicated as the two strands are separated. A significant portion of DNA (more than 98% for humans) is non-coding, meaning that these sections do not serve a function of encoding proteins.

The two strands of DNA run in opposite directions to each other and are therefore anti-parallel, one backbone being 3 (three prime) and the other 5 (five prime). This refers to the direction the 3rd and 5th carbon on the sugar molecule is facing. Attached to each sugar is one of four types of molecules called nucleobases (informally, bases). It is the sequence of these four nucleobases along the backbone that encodes biological information. Under the genetic code, RNA strands are translated to specify the sequence of amino acids within proteins. These RNA strands are initially created using DNA strands as a template in a process called transcription.

Within cells, DNA is organized into long structures called chromosomes. During cell division these chromosomes are duplicated in the process of DNA replication, providing each cell its own complete set of chromosomes. Eukaryotic organisms (animals, plants, fungi, and protists) store most of their DNA inside the cell nucleus and some of their DNA in organelles, such as mitochondria or chloroplasts.[1] In contrast, prokaryotes (bacteria and archaea) store their DNA only in the cytoplasm. Within the chromosomes, chromatin proteins such as histones compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed.

Scientists use DNA as a molecular tool to explore physical laws and theories, such as the ergodic theorem and the theory of elasticity. The unique material properties of DNA have made it an attractive molecule for material scientists and engineers interested in micro- and nano-fabrication. Among notable advances in this field are DNA origami and DNA-based hybrid materials.[2]

The obsolete synonym "desoxyribonucleic acid" may occasionally be encountered, for example, in pre-1953 genetics.

DNA is a long polymer made from repeating units called nucleotides.[3][4][5] DNA was first identified and isolated by Friedrich Miescher and the double helix structure of DNA was first discovered by James Watson and Francis Crick. The structure of DNA of all species comprises two helical chains each coiled round the same axis, and each with a pitch of 34ngstrms (3.4nanometres) and a radius of 10ngstrms (1.0nanometres).[6] According to another study, when measured in a particular solution, the DNA chain measured 22 to 26ngstrms wide (2.2 to 2.6nanometres), and one nucleotide unit measured 3.3 (0.33nm) long.[7] Although each individual repeating unit is very small, DNA polymers can be very large molecules containing millions of nucleotides. For instance, the largest human chromosome, chromosome number 1, consists of approximately 220 million base pairs[8] and is 85mm long.

In living organisms DNA does not usually exist as a single molecule, but instead as a pair of molecules that are held tightly together.[9][10] These two long strands entwine like vines, in the shape of a double helix. The nucleotide repeats contain both the segment of the backbone of the molecule, which holds the chain together, and a nucleobase, which interacts with the other DNA strand in the helix. A nucleobase linked to a sugar is called a nucleoside and a base linked to a sugar and one or more phosphate groups is called a nucleotide. A polymer comprising multiple linked nucleotides (as in DNA) is called a polynucleotide.[11]

The backbone of the DNA strand is made from alternating phosphate and sugar residues.[12] The sugar in DNA is 2-deoxyribose, which is a pentose (five-carbon) sugar. The sugars are joined together by phosphate groups that form phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar rings. These asymmetric bonds mean a strand of DNA has a direction. In a double helix the direction of the nucleotides in one strand is opposite to their direction in the other strand: the strands are antiparallel. The asymmetric ends of DNA strands are called the 5 (five prime) and 3 (three prime) ends, with the 5 end having a terminal phosphate group and the 3 end a terminal hydroxyl group. One major difference between DNA and RNA is the sugar, with the 2-deoxyribose in DNA being replaced by the alternative pentose sugar ribose in RNA.[10]

The DNA double helix is stabilized primarily by two forces: hydrogen bonds between nucleotides and base-stacking interactions among aromatic nucleobases.[14] In the aqueous environment of the cell, the conjugated bonds of nucleotide bases align perpendicular to the axis of the DNA molecule, minimizing their interaction with the solvation shell and therefore, the Gibbs free energy. The four bases found in DNA are adenine (abbreviated A), cytosine (C), guanine (G) and thymine (T). These four bases are attached to the sugar/phosphate to form the complete nucleotide, as shown for adenosine monophosphate.

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DNA - Wikipedia, the free encyclopedia

DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a persons body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).

The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.

DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladders rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.

An important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell.

DNA is a double helix formed by base pairs attached to a sugar-phosphate backbone.

The National Human Genome Research Institute fact sheet Deoxyribonucleic Acid (DNA) provides an introduction to this molecule.

Information about the genetic code and the structure of the DNA double helix is available from GeneEd.

The New Genetics, a publication of the National Institute of General Medical Sciences, discusses the structure of DNA and how it was discovered.

Next: What is mitochondrial DNA?

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What is DNA? - Genetics Home Reference - Your guide to ...

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Family Tree DNA - Official Site

DNA from the Beginning is organized around key concepts. The science behind each concept is explained by: animation, image gallery, video interviews, problem, biographies, and links. DNAftb blog: It's the season of hibernation, something I've always wished I could do. Oh, to wrap up in a ball, sleep away the winter, and wake to a beautiful spring day like Bambi! Although the thought has always intrigued me, it never really occurred to me what a feat hibernation actually is. It turns out that all of the bears, squirrels, rabbits ... that I thought were just sleeping, are breaking biological laws!! If I was to stay dormant for 5 months, without food or drink and little to no movement in freezing temperatures [...] Feature: We have relaunched the Weed to Wonder site as a flexible "e-book" that can be viewed as a website, an app, or a printable PDF. Mailing List Gene News - Scientists discover how leukemia cells exploit enhancer DNA elements to cause lethal disease Find the DNALC on: Language options:

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DNA from the Beginning - An animated primer of 75 experiments ...

DNA nanotechnology has become one of the great hopes of molecular manufacturing in which large-scale objects could potentially be assembled from the most basic building blocks, atom-by-atom. Research is slowly revealing that many of the assumptions about DNA manufacturing are accurate, such as the ability of meeting design specifications down to atomically precise accuracy.

In the latest development for DNA manufacturing, researchers at Purdue University have developed a DNA motor that can transport nanoparticles up and down a carbon nanotube. While protein-based motors are doing this all the time in biological systems, the DNA the researchers have developed marks the first time that a synthetic molecule has been used to accomplish the same feat.

The DNA-based motor does not travel as fast as a protein-based motor does, but it does have the benefit of being controlled, of operating outside its natural environment and can be switched on or off.

The research, which was published in the journal Nature Nanotechnology (A synthetic DNA motor that transports nanoparticles along carbon nanotubes), demonstrated that DNA enzymes could transport cadmium sulfide nanocrystals along the length of a single-walled nanotube, deriving energy to carry its cargo by eating up RNA left along its path.

"Our motors extract chemical energy from RNA molecules decorated on the nanotubes and use that energy to fuel autonomous walking along the carbon nanotube track," said Jong Hyun Choi, a Purdue University assistant professor of mechanical engineering, in a press release.

The DNA enzyme has a core and two arms that come out from the top and bottom of the core. Movement of the DNA occurs as that core of the DNA enzyme cleaves a strand off the RNA. After one strand of RNA has been sliced off, the upper arm of the DNA enzyme grabs onto another strand of RNA and pulls the entire body along.

When the researchers concede that the DNA is slower at moving then their protein-based counterparts, they arent kidding. It took 20 hours for the DNA motor to move down the length of the carbon nanotube, which was several microns long.

While the researchers believe that increasing the temperature and acidity of the environment could speed up the process, its not clear how much they could speed it up.

Its also not clear how RNA will always be around to help DNA motors to travel around in different environments. While molecular manufacturing adherents will no doubt be encouraged by this research, we may not need to worry about grey goo overrunning our planet as nanobots go about eating everything up to feed themselves.

Illustration: Tae-Gon Cha/Purdue University

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DNA Motor Transports Cargo Along Carbon Nanotube

Dec. 19, 2013 As part of an international research project, a team of researchers has developed a DNA clamp that can detect mutations at the DNA level with greater efficiency than methods currently in use. Their work could facilitate rapid screening of those diseases that have a genetic basis, such as cancer, and provide new tools for more advanced nanotechnology. The results of this research is published this month in the journal ACS Nano.

Toward a new generation of screening tests

An increasing number of genetic mutations have been identified as risk factors for the development of cancer and many other diseases. Several research groups have attempted to develop rapid and inexpensive screening methods for detecting these mutations. "The results of our study have considerable implications in the area of diagnostics and therapeutics," says Professor Francesco Ricci, "because the DNA clamp can be adapted to provide a fluorescent signal in the presence of DNA sequences having mutations with high risk for certain types cancer. The advantage of our fluorescence clamp, compared to other detection methods, is that it allows distinguishing between mutant and non-mutant DNA with much greater efficiency. This information is critical because it tells patients which cancer(s) they are at risk for or have."

"Nature is a constant source of inspiration in the development of technologies," says Professor Alexis Valle-Blisle. "For example, in addition to revolutionizing our understanding of how life works, the discovery of the DNA double helix by Watson, Crick and Franklin in 1953 also inspired the development of many diagnostic tests that use the strong affinity between two complementary DNA strands to detect mutations."

"However, it is also known that DNA can adopt many other architectures, including triple helices, which are obtained in DNA sequences rich in purine (A, G) and pyrimidine (T, C) bases," says the researcher Andrea Idili, first author of the study. "Inspired by these natural triple helices, we developed a DNA-based clamp to form a triple helix whose specificity is ten times greater than a double helix allows."

"Beyond the obvious applications in the diagnosis of genetic diseases, I believe this work will pave the way for new applications related in the area of DNA-based nanostructures and nanomachines," notes Professor Kevin Plaxco, University of California, Santa Barbara. "Such nanomachines could ultimately have a major impact on many aspects of healthcare in the future."

"The next step is to test the clamp on human samples, and if it is successful, it will begin the process of commercialization," concludes Professor Valle-Blisle.

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DNA clamp to grab cancer before it develops

DNA from an ancient toe bone has provided new insight into the lives of Neanderthals, revealing that inbreeding was common among the group and may have contributed to their demise.

Scientists sequenced DNA from a 50,000-year-old toe bone of a female Neanderthal, found in Denisova Cave in Siberia where fossilized remnants of human ancestors were found in 2010, according to the report in the journal Nature. The analysis suggested that her parents were genetically close enough to be either half siblings, first cousins or an uncle and a niece.

The findings suggest the population of Neanderthals was small, making inbreeding more common among them than among ancestors of modern humans, said David Reich, a study author and professor of genetics at Harvard Medical School in Boston. The low levels of genetic diversity also may have made them less fit over the long run, leading to their extinction, although that is still conjecture, Reich said.

We know these people were mixing with their close relatives, Reich said in a telephone interview. This seems to be something special about the Neanderthal population, it has this feature of inbreeding. We know this wasnt a single event.

Neanderthals were thought to have lived in Europe until 30,000 years ago, possibly overlapping with modern humans there, according to an accompanying editorial by Ewan Birney, a biologist at the Wellcome Trust Genome Campus in Cambridge, U.K. and Jonathan Pritchard, a geneticist at Stanford University in California.

The DNA analysis now provides researchers with a Neanderthal genome that can be studied to more closely track known interbreeding with other early human ancestors.

Early studies from incomplete DNA suggested that modern humans split off from Neanderthals and another, less-well-known cousin, the Denisovans, about 600,000 years ago. As technology improved, evidence was developed that ancestors of modern humans had, in fact, mated with Neanderthals. The Denisovans were discovered through DNA.

Although todays Neanderthal bone was found in the same cave as a Denisovan finger bone sequenced earlier, the two individuals werent closely related. The ancestors likely split from each other about 400,000 years ago.

In the genes, the scientists found evidence for a sequence thats different from any known group of human ancestors, suggesting that there may have been other hominids contributing genes.

It does seem that Eurasia during the Late Pleistocene was an interesting place to be a hominin, with individuals of at least four quite diverged groups living, meeting, and occasionally having sex, Birney and Pritchard wrote in their editorial.

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Ancient Toe Bone Shows Incest Role in Neanderthal Decline