文章来源:未知 文章作者:enread 发布时间:2011-01-21 06:45 字体: [ ]  进入论坛

Using a new experimental test structure, biophysicists at JILA have unraveled(解开,阐明) part of a 15-year mystery in the mechanics of DNA1—just how the molecule2 manages to suddenly extend to almost twice its normal length. The new test structure should support research on DNA elasticity3(弹性,弹力) as a standard for tiny forces and help refine studies of how drugs and other substances bind4 to DNA. In a new paper in the Journal of the American Chemical Society, JILA scientists disprove a leading explanation for DNA overstretching, a curious behavior in which the molecule's double helix(螺旋) structure suddenly extends by 70 percent when subjected to 65 picoNewtons (pN) of force. The exact steps of the process have been controversial since overstretching was discovered in 1996. Contrary to a popular theory, the new JILA work shows that DNA's backbone5 does not need to have a small gap, often called a nick, or sport loose ends for the dramatic extension to occur at 65 pN.

JILA is a joint6 institute of the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder7.

"Overstretching is a really amazing phenomenon, and even after 15 years, people are still debating it," says senior author Tom Perkins, a NIST expert in the mechanics of single molecules8. "DNA stretches and stretches like a rubber band and you think it's going to break, and then all of a sudden it nearly doubles in length. Something wonderfully interesting happens at this transition."

The leading theory is that overstretching introduces so much energy that the DNA melts, with a single strand9 peeling off(剥离) from nicks in the backbone or free ends. This model assumes that nicks or ends are essential. Scientists did not test this assumption until now because there was no platform for restraining the ends without also locking the molecule's structure and rotation10.

The JILA team's key advance was a clever geometry that binds11 a looped end of DNA to a micro-sized bead12, while the other end of the DNA has both strands13 stapled14 to a surface. Lasers apply force to the bead and measure its position. The DNA has freedom to rotate but, crucially, no loose ends.

The researchers compared one piece of DNA without nicks or free ends to another piece of DNA they had nicked. They found that both molecules overstretched at essentially15 the same force, indicating the same mechanism16 is at work in both cases.

In addition to narrowing the focus of debate about overstretched DNA, Perkins says the findings and the new DNA test structure will support NIST efforts to develop an official picoNewton-scale force standard that is traceable to the International System of Units. A picoNewton is one-trillionth of a newton, the unit of force; one newton is roughly the weight of a small apple. DNA is already used informally as a calibration standard for atomic force microscopes. Further JILA studies are planned.


1 DNA 4u3z1l     
(缩)deoxyribonucleic acid 脱氧核糖核酸
  • DNA is stored in the nucleus of a cell.脱氧核糖核酸储存于细胞的细胞核里。
  • Gene mutations are alterations in the DNA code.基因突变是指DNA密码的改变。
2 molecule Y6Tzn     
  • A molecule of water is made up of two atoms of hygrogen and one atom of oxygen.一个水分子是由P妈?f婘??妈?成的。
  • This gives us the structural formula of the molecule.这种方式给出了分子的结构式。
3 elasticity 8jlzp     
  • The skin eventually loses its elasticity.皮肤最终会失去弹性。
  • Every sort of spring has a definite elasticity.每一种弹簧都有一定的弹性。
4 bind Vt8zi     
  • I will let the waiter bind up the parcel for you.我让服务生帮你把包裹包起来。
  • He wants a shirt that does not bind him.他要一件不使他觉得过紧的衬衫。
5 backbone ty0z9B     
  • The Chinese people have backbone.中国人民有骨气。
  • The backbone is an articulate structure.脊椎骨是一种关节相连的结构。
6 joint m3lx4     
  • I had a bad fall,which put my shoulder out of joint.我重重地摔了一跤,肩膀脫臼了。
  • We wrote a letter in joint names.我们联名写了封信。
7 boulder BNbzS     
  • We all heaved together and removed the boulder.大家一齐用劲,把大石头搬开了。
  • He stepped clear of the boulder.他从大石头后面走了出来。
8 molecules 187c25e49d45ad10b2f266c1fa7a8d49     
分子( molecule的名词复数 )
  • The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。
  • Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里,大分子裂变为小分子。
9 strand 7GAzH     
  • She tucked a loose strand of hair behind her ears.她把一缕散发夹到了耳后。
  • The climbers had been stranded by a storm.登山者被暴风雨困住了。
10 rotation LXmxE     
  • Crop rotation helps prevent soil erosion.农作物轮作有助于防止水土流失。
  • The workers in this workshop do day and night shifts in weekly rotation.这个车间的工人上白班和上夜班每周轮换一次。
11 binds c1d4f6440575ef07da0adc7e8adbb66c     
v.约束( bind的第三人称单数 );装订;捆绑;(用长布条)缠绕
  • Frost binds the soil. 霜使土壤凝结。 来自《简明英汉词典》
  • Stones and cement binds strongly. 石头和水泥凝固得很牢。 来自《简明英汉词典》
12 bead hdbyl     
  • She accidentally swallowed a glass bead.她不小心吞下了一颗玻璃珠。
  • She has a beautiful glass bead and a bracelet in the box.盒子里有一颗美丽的玻璃珠和手镯。
13 strands d184598ceee8e1af7dbf43b53087d58b     
n.(线、绳、金属线、毛发等的)股( strand的名词复数 );缕;海洋、湖或河的)岸;(观点、计划、故事等的)部份v.使滞留,使搁浅( strand的第三人称单数 )
  • Twist a length of rope from strands of hemp. 用几股麻搓成了一段绳子。 来自《简明英汉词典》
  • She laced strands into a braid. 她把几股线编织成一根穗带。 来自《简明英汉词典》
14 stapled 214b16946d835ee84f23c29ab8689fa8     
v.用钉书钉钉住( staple的过去式和过去分词 )
  • The letter was stapled to the other documents in the file. 这封信与案卷里的其他文件钉在一起。 来自辞典例句
  • He said with smooth bluntness and shoved a stack of stapled sheets across his desk. 他以一种圆滑、率直的口气说着,并把一叠订好了的稿纸从他办公桌那边递过来。 来自辞典例句
15 essentially nntxw     
  • Really great men are essentially modest.真正的伟人大都很谦虚。
  • She is an essentially selfish person.她本质上是个自私自利的人。
16 mechanism zCWxr     
  • The bones and muscles are parts of the mechanism of the body.骨骼和肌肉是人体的组成部件。
  • The mechanism of the machine is very complicated.这台机器的结构是非常复杂的。
TAG标签: energy DNA molecule