2013年4月10日星期三

which have been coded to match the PNA

The human body constantly reads genetic code off of DNA, otherwise know as deoxyribonucleic acid, onto RNA, or ribonucleic acid, and then uses ribosomes, cellular structures, to translate genetic code and build a chain of amino acids linked in a specific order. These molecular chains are called proteins. Because proteins are comprised of a series of linked molecular units, they are examples of molecular chains called polymers.

“The idea of trying to turn the information in DNA sequences into materials other than proteins has been an aspiration of chemists and chemical biologists for quite some time,” said Liu. “Previous efforts to use DNA to direct polymer synthesis have largely been limited to the synthesis of nucleic acids or nucleic acid-like polymers, such as DNA, RNA, or peptide nucleic acids, or PNA.”

This study, published in the journal Nature Chemistry, demonstrates for the first time a method of creating entire non-nucleic acid polymers directly from the code on DNA. Previously, non-nucleic acid polymers had to be built stepwise,Offering discount stainless steel cufflink and other mens accessories including pendants. by adding one new unit to the polymer’s end each time. In this method, building a ten-unit polymer would take ten separate steps. Using Liu’s method could reduce the number of steps and the time required.

“Biological polymers have many special properties, such as the ability to catalyze chemical reactions, to fold into specific shapes, and to have specific dynamic properties because of their precise sequence-defined structure,” Liu said. “Just like beads on a string, each building block is installed in a precise order to generate a biological polymer.”

The technique presented by Liu’s team works by attaching a piece of specifically coded PNA to a building block of a biological polymer. In this way, each unit of one type can be identified by a short PNA code. Several different PNA-labeled building blocks are then introduced into a system with DNA templates, which have been coded to match the PNA labels and order them precisely. Thus, the DNA lines up each separate building block in a sequence-defined order so the polymer chain is primed for attachment in one step.

Building such polymers is relatively easy due to the structural similarity of DNA and other nucleic acids, allowing them to bind naturally in a specific order. Using PNA “adapters” to bind these building blocks, Liu used a coded strand of DNA to put together any family of linkable blocks, regardless of structure.

Liu stated that the implications of this work lie in the ability to create libraries of millions or billions of these polymers and DNA templates more efficiently. Having these libraries would facilitate evolving these polymers. Liu’s group plans to screen these polymers for desirable properties, such as activation of certain genes, in a process that he said will approximate Darwinian evolution.

Before you can learn capoeira in Fabio “Fua” Nascimento’s class, you have to learn a little Portuguese. At the beginning of each session, he passes out instruments — a drum, a cowbell, a tambourine — and tells his students to repeat after him, his big voice soaring: A maré tá cheia ioio, or “The tide is high.”

Briefly, it feels like a sing-along rather than a martial-arts class. But within minutes the instruments are set down, and participants are lunging across the floor — kicking, jumping, back bending, ducking and, eventually, contorting their bodies into a kind of backward cartwheel.

The surprising intersection of music, singing, dancing and fighting is unique to capoeira. The Brazilian “fight-dance” can be traced back to the 1600s, when landowners, faced with an increasing number of runaway slaves, allowed their African workers to dance and practice their religion twice a month. What the slaves created was a sly martial art, characterized by rhythm and fluid movement — and dressed up as a dance.

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