【每日阅读训练第四期——速度越障10系列】【10-16】科技

CHRISTINE2010

【计时一】

Engineered Bacteria Can Make the Ultimate Sacrifice for the Good of the Population

ScienceDaily (Nov. 20, 2012) — Scientists have engineered bacteria that are capable of sacrificing themselves for the good of the bacterial population. These altruistically inclined bacteria, which are described online in the journal Molecular Systems Biology, can be used to demonstrate the conditions where programmed cell death becomes a distinct advantage for the survival of the bacterial population.
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"We have used a synthetic biology approach to explicitly measure and test the adaptive advantage of programmed bacterial cell death in Escherichia coli," said Lingchong You, senior author of the study and an associate professor at the Department of Biomedical Engineering, Duke University, and the Duke Institute for Genome Sciences & Policy. "The system is tunable which means that the extent of altruistic death in the bacterial population can be increased. We are therefore able to control the extent of programmed cell death as well as test the benefits of altruistic death under different conditions." The lead author of the study is Yu Tanouchi, a graduate student in the Department of Biomedical Engineering. Anand Pai and Nicolas Buchler also contributed to the work.

Scientists have known for some time that programmed cell death can be linked to the response of bacteria to stressful conditions, for example starvation of amino acids or the presence of competitor molecules. However, it is not clear why cells should choose to die under such conditions since it gives them no immediate advantages. Some researchers have suggested that programmed cell death allows cells to provide benefits to their survivors but until now it has been difficult to test this directly in experiments.

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【计时二】

The researchers used synthetic biology procedures to engineer Escherichia coli in such a way that the bacterial cells are capable of suicidal behavior and promoting the good of the bacterial population. To do so they introduced a gene circuit, which consists of two modules, into the bacteria. If the "suicide module" is active it leads to the rupture and death of some bacterial cells when they are challenged with the antibiotic 6-aminopenicillanic acid. If the "public good" module is expressed, a modified form of the enzyme beta-lactamase is produced, which protects surviving cells from rupture or lysis by breaking down the antibiotic. This protection only occurs when the enzyme is released from inside the bacterial cells that make the ultimate sacrifice and die after rupture.

"Our results clearly demonstrate that it is possible to have conditions where the death of some bacteria confers an advantage for the overall population of bacteria," remarked You. "The optimal death rate for the bacterial population emerges after sufficient time has passed and is clearly visible in our system."

The scientists were also able to provide a possible explanation for the "Eagle effect," an unexpected phenomenon where bacteria appear to grow better when treated with higher antibiotic concentrations. "Overall our results fill in a conceptual gap in understanding the evolutionary dynamics of programmed bacterial death during stress and have implications for designing intervention strategies for effective treatment of bacterial infections with antibiotics," concluded You.

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【计时三】

Synthetic Membrane Channels Built out of DNA: Nanotech Structures Mimic Nature's Way of Tunneling Through Cell Walls

ScienceDaily (Nov. 20, 2012) — As reported in the journal Science, physicists at the Technische Universitaet Muenchen (TUM) and the University of Michigan have shown that synthetic membrane channels can be constructed through "DNA nanotechnology." This technique employs DNA molecules as programmable building materials for custom-designed, self-assembling, nanometer-scale structures. The researchers present evidence that their nature-inspired nanostructures may also behave like biological ion channels. Their results could mark a step toward applications of synthetic membrane channels as molecular sensors, antimicrobial agents, and drivers of novel nanodevices.
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Over the past three decades, researchers have advanced DNA nanotechnology from an intriguing idea to an emerging technology, with a toolbox of methods and a portfolio of nanometer-scale objects designed to demonstrate its potential. What's new here is the claim that DNA nanotech can be used to mimic one of the most widespread and important nanomachines in nature.
To wall off the insides of cells from the outside world, organisms in all three domains of life use the same kind of barrier: an impermeable membrane made from two layers of lipid molecules. Such membranes can also be found within cells, for example encapsulating the nucleus, and even surrounding many kinds of viruses. And to mediate between the different environments on either side of this universal barrier, nature provides a common type of passageway. Membrane channels are tube-like structures made of proteins, which pierce the barriers and regulate the two-way exchange of material and information between the inside and outside. Now researchers have demonstrated the first artificial membrane channel made entirely of DNA, and its characteristics suggest a number of potential applications. "If you want, for example, to inject something into a cell, you have to find a way to punch a hole into the cell membrane, and this device can do that, at least with model cell membranes," says TUM Prof. Hendrik Dietz, a fellow of the TUM Institute for Advanced Study.
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In a shape inspired by a natural channel protein, the DNA-based membrane channel consists of a needle-like stem 42 nanometers long with an internal diameter of just two nanometers, partly sheathed by a barrel-shaped cap. A ring of cholesterol units around the edge of the cap helps the device "dock" to a lipid membrane while the stem sticks through it, forming a channel that appears to function like the real thing. TUM Professor Friedrich Simmel, co-coordinator of the Excellence Cluster Nanosystems Initiative Munich, explains: "We have not tested this yet with living cells, but experiments with lipid vesicles show that our synthetic device will bind to a bilayer lipid membrane in the right orientation, so that the stem both penetrates the membrane and holds at the surface, forming a pore."
Further experiments demonstrated that the resulting pores have electrical conductivity comparable to that of a natural cell wall with ion channels, suggesting that they might be able to act like voltage-controlled gates. The results also suggest that transmembrane current could be tuned by adjusting fine structural details of the synthetic channels. To test one potential application of the DNA nanotech devices, the researchers used them as "nanopores" for several different molecular sensing experiments. These confirmed that it is possible, by observing changes in the electrical characteristics, to record the passage of single molecules through synthetic membrane channels made from DNA. Because this approach allows both geometric and chemical tailoring of the membrane channels, it might offer advantages over two other families of molecular sensors, based on biological and solid-state nanopores respectively.
Other conceivable applications remain to be investigated. One notion is to imitate the action of viruses or phages, breaking through the cell walls of targeted bacteria to kill them. In gene therapy, synthetic membrane channels might be used as nano-needles to inject material into cells. Such channels could also be used in basic studies of cell metabolism. Another idea is to harness the so-called ion flux -- which in cell membranes moves material in and out through the channel -- to drive sophisticated nanodevices inspired by other natural mechanisms. "We might be able to mimic natural ion pumps, transport proteins, and rotary motors like the enzyme responsible for synthesizing ATP," says Dietz. "I love that idea. That's what keeps me running."
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【计时五】

Hot Gas Bridges Galaxy Cluster Pair

ScienceDaily (Nov. 20, 2012) — ESA's Planck space telescope has made the first conclusive detection of a bridge of hot gas connecting a pair of galaxy clusters across 10 million light-years of intergalactic space.
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Planck's primary task is to capture the most ancient light of the cosmos, the Cosmic Microwave Background, or CMB. As this faint light traverses the Universe, it encounters different types of structure including galaxies and galaxy clusters -- assemblies of hundreds to thousands of galaxies bound together by gravity.
If the CMB light interacts with the hot gas permeating these huge cosmic structures, its energy distribution is modified in a characteristic way, a phenomenon known as the Sunyaev-Zel'dovich (SZ) effect, after the scientists who discovered it.
This effect has already been used by Planck to detect galaxy clusters themselves, but it also provides a way to detect faint filaments of gas that might connect one cluster to another.
In the early Universe, filaments of gaseous matter pervaded the cosmos in a giant web, with clusters eventually forming in the densest nodes.
Much of this tenuous, filamentary gas remains undetected, but astronomers expect that it could most likely be found between interacting galaxy clusters, where the filaments are compressed and heated up, making them easier to spot.
Planck's discovery of a bridge of hot gas connecting the clusters Abell 399 and Abell 401, each containing hundreds of galaxies, represents one such opportunity.
The presence of hot gas between the billion-light-year-distant clusters was first hinted at in X-ray data from ESA's XMM-Newton, and the new Planck data confirm the observation.
It also marks Planck's first detection of inter-cluster gas using the SZ effect technique.
By combining the Planck data with archival X-ray observations from the German satellite Rosat, the temperature of the gas in the bridge is found to be similar to the temperature of the gas in the two clusters -- on the order of 80 million degrees Celsius.
Early analysis suggests the gas could be mixture of the elusive filaments of the cosmic web mixed with gas originating from the clusters.
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【越障】

Mars Formed from Similar Building Blocks to That of Earth, Reveals Study of Martian Meteorites

ScienceDaily (Nov. 19, 2012) — A team of scientists, including Carnegie's Conel Alexander and Jianhua Wang, studied the hydrogen in water from the Martian interior and found that Mars formed from similar building blocks to that of Earth, but that there were differences in the later evolution of the two planets. This implies that terrestrial planets, including Earth, have similar water sources--chondritic meteorites. However, unlike on Earth, Martian rocks that contain atmospheric volatiles such as water, do not get recycled into the planet's deep interior.
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Their work will be published in the December 1 issue of Earth and Planetary Science Letters.
Much controversy surrounds the origin, abundance and history of water on Mars. The sculpted channels of the Martian southern hemisphere speak loudly of flowing water, but this terrain is ancient. Consequently, planetary scientists often describe early Mars as "warm and wet" and current Mars as "cold and dry."
Debate in the scientific community focuses on how the interior and crust of Mars formed, and how they differ from those of Earth. To investigate the history of Martian water and other volatiles, scientists at NASA's Johnson Space Center in Houston, Carnegie, and the Lunar and Planetary Institute in Houston studied water concentrations and hydrogen isotopic compositions trapped inside crystals within two Martian meteorites. The meteorites, called shergottites, were of the same primitive nature, but one was rich in elements such as hydrogen, whereas the other was depleted.
The meteorites used in the study contain trapped basaltic liquids, and are pristine samples that sampled various Martian volatile element environments. One meteorite appears to have changed little on its way from the Martian mantle up to the surface of Mars. It has a hydrogen isotopic composition similar to that of Earth. The other meteorite appears to have sampled Martian crust that had been in contact with the Martian atmosphere. Thus, the meteorites represent two very different sources of water. One sampled water from the deep interior and represents the water that existed when Mars formed as a planet, whereas the other sampled the shallow crust and atmosphere.
"There are competing theories that account for the diverse compositions of Martian meteorites," said lead Tomohiro Usui. "Until this study there was no direct evidence that primitive Martian lavas contained material from the surface of Mars."
Because the hydrogen isotopic compositions of the two meteorites differ, the team inferred that martian surface water has had a different geologic history than Martian interior water. Most likely, atmospheric water has preferentially lost the lighter hydrogen isotope to space, and has preferentially retained the heavier hydrogen isotope (deuterium).
That the enriched meteorite has incorporated crustal and atmospheric water could help to solve an important mystery. Are Martian meteorites that are enriched in components, such as water, coming from an enriched, deep mantle, or have they been overprinted by interaction with the Martian crust?
"The hydrogen isotopic composition of the water in the enriched meteorite clearly indicates that they have been overprinted, so this meteorite tells scientists more about the Martian crust than about the Martian mantle," Alexander said. "Conversely, the other meteorite yields more information about the Martian interior."
The concentrations of water in the meteorites are also very different. One has a rather low water concentration and that means that the interior of Mars is rather dry. Conversely, the enriched basalt has 10 times more water than the other one, suggesting that the surface of Mars could have been very wet at one time. Therefore, scientists are now starting to learn which meteorites tell us about the Martian interior and which samples tell us about the Martian surface.
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flyoceanwu

thank you christine!没想到我竟然是第1个来分队的。

1 1‘43“

3 2'16 DNA Nanotechnology construct synthetic membrane.

4 2'34"

5 1‘58“

6 越障：5’32
study water that from martian interior different from water on earth.
there is controversary about surround origin abund and deep history of water.Martinrocks contain atmospheric volaticles not recycle from interior of mars.
scientist still  research  which martian interior and which sample tell about martian surface.

Victoriasong

1.23
1.14
1.47
1.36
3.28
今天读得有点快

铁板神猴

辛苦了~ 来拜读一下
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1'24''
1'24''
2'00''
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2'24''

3'54''

attractg

占位，占位！！！  Chritine 辛苦！

速度：
2’34’’(276) Engineered cells died for the good of the population. Programmed cells died can be an advantage to the cell population. This kind of cell is altruistic… If the group is tunable, which means the extent of altruistic death in population could be increase. Programmed cells died are response to the pressure in environment.

1’50’’(266) The scientists used a synthetic biological method to create EC, a cell suicide and provide advantage of the cell population. Scientists said it is possible to have some conditions where they found that the death of programmed cells provide some benefits of whole population. “Eagle effect”: a bacteria can grow well when there are more antibiotics in the environment.

2’30’’(334) Scientists have found synthetic membrane channels can be constructed by “nanotechnology”. Scientists have many objects to test its potential. In three dominates of life, all the membrane consists of one impermeable cell wall made of two lipids of liquid molecules.

2’58’’(328) The DNA based-channel consist of 42 stem-liked …. Other applications still need to be tested. One is imitate the behaviors of virus… Another is to harness the so-called ion flux…

2’03’’(350) The ESA’s telescope has made the first conclusive detection of a bridge of hot gas connecting a pair of galaxy cluster…

越障：
4’32’’(616)
Main Idea：Mars formed from the similar building blocks to that of the Earth
Author’s attitude: Neutral
Structure:
>> Mars and earth formed from similar building blocks, but there are differences in later evolution of the two planets.
>> Debate in scientists focus on how the interior and atmosphere of the Mars formed, and how different it is from Earth
Method:
Scientists study Mars by trapping hydrogen isotopic compositions in two Mars meteorites.
One meteorite is full of hydrogen…. Changed little in Mars’ surface…
Another meteorite is deplete of hydrogen, began interact with Mars’ atmosphere…
Two meteorites represent two source of water.
Scientists inferred the water on surface of Mars has a different geologic history than Martian interior water
>> Enriched meteorites solve an important mystery .
Are enriched elements on surface of Mars from deep inside mantle , or overprinted by interactions on Mars curst ?

xiaodiehoo

有几天没上，我又回来了
今天第二次考G，还是没能上7， 自己感觉提高很多，考场上也感觉做得还行，结果成绩还是不理想……
继续跟小分队练习

alun1987

回家真好，终于有网上了……谢谢LZ分享文章

1'14
1'16
1'58
2'21
1'55

越障：
1).summarize the study and findings:
study the H in water from interior of Mars, find that Mars and Earth are similar in building blocks, but differ in later evolution.
it conclude that the source of water might be the same, but Mars is not involved in the deep interior recycle.

2).problems identification:history of the Martian water
much controversy...according to scientists, past: warm and wet; now:cold and dry

3).study and findings:
study the water concentration and H in composition within two meteorites
-one rich in elements, from mantle→water from deep interior, when the Mars formed
-one depleted, touch atm→shallow and atm

4).inferences and applications:
surface water and interior water have differences in geology histories; surface water lost the lighter H, and kept the heavier ones.

where does the component enriched meteorites come from?surface or interior? surface overprinted

5).remaining problems and further research:
concentration of water in meteorites: inferior dry but surface wet, need to decide which meteorite tells about where...

Daisy汪

1‘23
1’
1‘32
1’17
1‘57

越障：
3’06
structure：
1.the structure of the surface of the mars and earth has sth in common
2.mars has more water in the surface than earth has, interior environment may be dry (martain contains a lot of water, martain consist most of the surface)
3.according to research, the water in mars has 2 sources.
4.scientists work hard to see whether there is differences between the surface and inter structure in mars

srafcatt

1'56 【276】
Bacteria decides suiside to survive the bacteria population,scientists wonder why.

1'36【266】
This programmed cell death procedure can be measured and controlled,but sometimes eagle effect happens.


【334】
Synthetic mambrane channels which have a lot of potential and are significant in many fields can be constructed through DNA nanotechnology.


【计时四】
2'
The membrane channel consists of a stem with a ring of cholesterol.DNA nanadevices can replace the channel and offer advantage over molecular sensors.
Application of DNA nanadevices include killing cells,  using as nanoneedles or studing cell metabolism,even drive sophisticated nanodevices.
【382】


2'04【350】

Sunyaev-Zel'dovich (SZ) effect has already been used by Planck to detect galaxy clusters  and faint filaments of gas.The presence of hot gas between the billion-light-year-distant clusters was first hinted.


【越障】4'34【616】
opinion newly found:
Mars formed from similar building blocks to that of Earth, but water on Mars won't be recycled to the interior.
There's a debate:
It focuses on how the interior and crust of Mars formed, and how they differ from those of Earth.
Two martian meteorites:
They show that the geologic history of martian surface and of interior water is different.

1.Most likely, atmospheric water has retained hydrogen isotope,which has been overprinted with the crust.
2.While other meterites mostly comes from the deep interior.
3.Which meteorite represent information from which place is still unknown.

徒手破鲜橙

占座，等会吃完饭来做阅读