As reported here numerous times (e.g., 06/14/2004, 12/04/2003, 04/14/2003, 03/28/2003, 02/25/2003, 12/17/2002, 09/26/2002, 03/26/2002, 02/01/2002, 12/06/2001, 08/17/2001, 06/19/2001, 02/21/2001), cells have an elaborate interstate highway system with molecular trucks hauling cargo back and forth. Scientists have known that the cellular highways have polarities labeled plus and minus, and that molecular motors typically go one way. Some motors, like kinesin, drive only in the plus direction, while others, like dynein, go in the minus direction. Now, it is becoming apparent that most pieces of cargo have at least one of each kind of motor, with a stickshift that allows it to drive in forward or reverse. The state of our knowledge about bidirectional transport is explored by Michael Welte in the July 13 issue of Current Biology.1 Welte examines the evidence that many, maybe all, moving cargoes have bidirectional ability. In the microscope, certain organelles like mitochondria and melanosomes are seen to move back and forth rapidly, eventually making it to their target. Why is this, and how is it done? Does the organelle grab motors out of the cytoplasm? Are both motors working in a tug-o’war? Welte cites evidence against these possibilities, and suggests (although hard evidence needs to be found), that the cargo carries both motors, and a “complex coordination machinery … ensures that when one motor is actively engaged with the microtubule, the other motor is turned off.” Moreover, this coordination machinery, whatever it is, may be under the influence of regulatory enzymes. “If the coordination machinery can attach to cargo independent of the motors,” he surmises, “distinct variants of the coordination machinery could be targeted to different cargoes, thus allowing cargo-specific coordination and regulation.” It seems odd, though, that cargoes would undergo a back-and-forth random walk instead of making a beeline to the target. Welte figures there must be biological justification for this behavior, so he examines some possibilities:Economy: “If cargoes always carry motors for both directions, net transport can easily be adjusted or even reversed by simply tweaking the relative activity of the two motors. This is likely to be much quicker than assembling a new set of motors on a cargo, and also allows transport to be abruptly altered depending on cellular needs. It even makes it possible to tune the overall speed of transport by altering the relative contribution of trips in the non-dominant direction.”Setting Up Polarized Distributions: “Sometimes it is necessary to set up a distribution rather than to confine the organelles to a single point …. Even if cargoes accumulate at a certain point (e.g. near plus-ends when motion is biased in the plus-end direction), trips in the non-dominant direction will tend to spread the cargoes out along the tracks, away from the point of accumulation. Modeling shows that by altering the relative contributions of plus- and minus-end trips, a wide range of steep to flat steady-state distributions can be achieved.”Avoiding Obstacles and Exploring Space: “As cytoplasmic dynein often steps sidewise to adjacent proto-filaments, a bidirectional cargo could find itself on the opposite side of the microtubule even after a short minus-end excursion. If it now switches back to kinesin I, it can pass the obstacle. Bidirectionally moving cargoes should, therefore, be less likely to contribute to disastrous traffic jams …. The random walk of bidirectional cargoes allows a single cargo to explore a large region of cellular space, especially if tracks are disordered.”Error Correction: “During unidirectional transport, the critical event that determines directionality of motion is the attachment to either a plus- or minus-end motor. A wrong attachment will cause misdelivery of the cargo. During bidirectional transport, the net direction of transport is determined by the balance of plus- and minus-end trips and can, therefore, be continually evaluated and even altered if physiological conditions change. Thus, bidirectional transport may facilitate error correction.It must be remembered that these motors are operating in the dark without eyes, like automated railroad cars. They don’t have sentient drivers on radios, but rather respond to chemical signals in the environment. Apparently these behaviors achieve the best solution to many complex problems. “Bidirectional transport by opposite-polarity microtubule motors is just one example of multiple motors working together to achieve carefully choreographed transport,” Welte says, as he concludes with a list of open problems needing further elucidation.1Michael A. Welte, “Bidirectional Transport along Microtubules,” Current Biology, Volume 14, Issue 13, 13 July 2004, Pages R525-R537, http://dx.doi.org/10.1016/j.cub.2004.06.045.Think of a 12-year-old kid on motorized rollerblades, one foot going forward, the other reverse. Imagine the tricks he could accomplish (with a little practice) switching from one foot to the other (or the bloody knees as he experiments the first time). Now make the wheels run on monorails. Imagine a complex tangle of rails, some blue, some red, going off in all directions, more dizzying than an amusement park roller coaster. The kid is supposed to put the left foot on the red rails and the right foot on the blue rails (one foot at a time, of course). Now hand him a package to deliver, and put a thousand other kids on the system going in all directions with packages of their own. The rails are also in constant motion, some growing and some shrinking. If the mental picture is becoming too complicated to dwell on further, just realize that something like this is happening in every cell of your body right now. This intracellular transport system is only a small part of a miniaturized city with many other vital tasks being performed flawlessly. The transportation system alone has a large infrastructure of support services. There are linemen for the monorails, pit crewmen for motor repair, traffic cops, construction crews, shippers, receivers and much more, without even considering what the cargoes are and what they do when they arrive. The interior of a cell is a whirlwind of constant activity, all necessary just to sustain life. Rocks do not do this. Evolutionists may jawbone about these systems emerging from chance and natural selection over millions of years of purposeless motion, but the more we can exhibit the details of cellular perfection, the less plausible their story is going to seem to any rational observer. This system is crying out for visualization. The wonder of intracellular transport would come alive if magnified a million times.2(Visited 10 times, 1 visits today)FacebookTwitterPinterestSave分享0
Share Facebook Twitter Google + LinkedIn Pinterest South Africa started accepting U.S. pork exports in February. NPPC, which worked with the Obama administration to convince the African nation to lift a de facto ban on U.S. pork, welcomed the news.The United States can ship to South Africa a variety of raw, frozen pork, including bellies, hams, loins, ribs and shoulders, for unrestricted sale and other pork for further processing. South Africa imposed a number of restrictions on pork imports, including one to prevent the spread of Porcine Reproductive and Respiratory Syndrome (PRRS) to South African livestock even though the risk of disease transmission from U.S. pork products is negligible.There is no documented scientific case of PRRS being transmitted to domestic livestock through imported pork. (New Zealand, a PRRS-free nation, imported pork for 10 years from PRRS-positive countries without getting the disease.) In early January, after the Obama administration threatened to suspend its trade benefits under the African Growth and Opportunity Act — duty-free access for products exported to the United States — South Africa announced it would partially lift its ban on U.S. pork. NPPC will continue to work with the governments in Washington and Pretoria to get the South African market fully opened to U.S. pork.
IT + Project Management: A Love Affair Cognitive Automation is the Immediate Future of… alex williams Related Posts Massive Non-Desk Workforce is an Opportunity fo… Tags:#Analysis#enterprise#news#NYT 3 Areas of Your Business that Need Tech Now Steve Ballmer is not shy about switching out management of the Windows Azure group. First we saw Ray Ozzie leave Microsoft. He left after Windows Azure became part of Bob Muglia’s responsibilities. Now Muglia is no longer the executive Ballmer wants to run the Server & Tools Business (STB), the division that oversees Windows Azure. In turn, Muglia will also be leaving Microsoft after the transition to new leadership.Ballmer’s new choice to lead STB depends on who has the experience to manage what the group sees as its main goals for the year ahead and beyond. It’s a critical decision. Ballmer has made the point often that the cloud represent Microsoft’s future.A quick look at the jobs Microsoft has open in the STB group gives insight into what that future may look like. STB is arguably the fastest growing part of the company. In the past week alone, there have been about 100 new job listings for positions in the division. Muglia’s position is not listed there but you can see what kind of roles are being developed and the skill sets required to do the work. Matching those job descriptions to the direction of the group and you can start to see some patterns.In particular, you see the leadership established by Muglia and Ozzie. Ozzie set the vision for Windows Azure and in many respect, Muglia served as its general, executing on the strategy.Under their successful leadership, Azure has moved from a cloud platform to one that seeks to extend into the all devices, embedded in every aspect of our lives. It’s an approach that means Windows 7 and Windows Phone 7 devices will have a future tied to the cloud. Mobile proliferation, smart operating systems and distributed networks are trends that will last at least a decade. You can see the influence of these movements in multiple ways on the Windows Azure group.Most of the positions we see on the Microsoft job search site are in software engineering. The team is also in need for people to do Web development, program management, consulting, operations, IT, marketing, research and sales. There are a few, though, that tell a larger story about Windows Azure future direction.For example, a marketing management position gives deeper insights into how these trends play into the Azure strategy and what the new leader will need to do in order to succeed. The description is testament to the influence the Windows Azure leadership has had on the group’s direction. The description refers to a post by Ray Ozzie about the paradigm of continuous services and connected devices. If you will recall, we wrote last week about a Flickr app on Windows 7 and Windows Phone 7 that synchronizes, in particular for a smartphone or tablet device. We are told this will be an ongoing story for Microsoft in the year ahead.Here’s the lead to a description for the marketing manager position:Do you want to join one of the fastest growing and energized groups at Microsoft? Are you interested in Microsoft’s strategy for expanding Windows and the Cloud to Specialized Devices? These Specialized Devices range from in-car infotainment systems, Digital Signage, Enterprise Handheld, Point of Service, Thin Clients, Industrial Controllers, Server Appliances, Connected TV and more. The Windows Embedded Business is impacting a number of industry and vertical segments including Automotive, Retail, Medical, Industrial Automation, Energy, Safety and Surveillance, and Consumer Electronics. The devices and scenarios our product and service enable are at the forefront Ray Ozzie’s “Continuous services / Connected Devices” paradigm (see http://ozzie.net/docs/dawn-of-a-new-day for more).From this we see a strategy that is moving off the PC and to the device. It plays into the need to develop services for the automobile, industrial equipment, consumer electronics and other devices.R “Ray” Wang, principal analyst and CEO of the Constellation Group, said that Muglia has been instrumental in building out the Azure group. His absence will be greatly missed.“Bob was instrumental in Microsoft building out its cloud strategy,” Wang said in an interview today. “A lot of the stuff he was doing on Azure was foundational to Microsoft’s future.”From our perspective, this seems more like a cultural shift. The world of connected devices and synchronized continuous services may be better lead by someone who has had a deeper role in developing a new generation of technologies more suited to a distributed world than the one where the PC was the once and only king.
UPDATED on June 25, 2018Most green builders include some type of mechanical ventilation system in every home they build. That’s good. Since green buildings usually have very low levels of air leakage, mechanical ventilation is usually essential.Unfortunately, several research studies have shown that a high number of mechanical ventilation systems are poorly designed or installed. Among the common problems:It’s disheartening to learn that many green homes waste energy because of poorly designed ventilation systems that were improperly commissioned.If you’re unfamiliar with residential ventilation systems, it’s a good idea to review the ventilation information in the GreenBuildingAdvisor encyclopedia.ASHRAE’s residential ventilation standard (Standard 62.2) sets the minimum ventilation rate at 7.5 cfm per occupant plus 3 cfm for every 100 square feet of occupiable floor area.The residential ventilation requirements in the 2018 International Residential Code (IRC) differ from the requirements of the ASHRAE 62.2 standard, however. According to the 2018 IRC, the minimum ventilation rate is 7.5 cfm per occupant plus 1 cfm for every 100 square feet of occupiable floor area. (For more information on code requirements for ventilation, see “An Update on the Residential Ventilation Debate.”)Systems complying with ASHRAE 62.2 have ventilation rates that are relatively low; for example, a 2,000-square-foot house with three occupants requires 83 cfm of mechanical ventilation. That’s about as much airflow as is provided by a typical bath exhaust fan. (Of course, systems complying with the minimum requirements of the 2018 IRC have even lower ventilation rates.)Since ventilation airflows are typically quite low, ventilation ductwork needs to be impeccably sealed. If ventilation ductwork is leaky, fresh air won’t reach its intended destination.Prominent building scientists are now debating the merits of the ASHRAE 62.2 ventilation rate. Max Sherman, former chairman of the ASHRAE 62.2 committee, defends the existing ASHRAE formula. On the other hand, Joseph… Sign up for a free trial and get instant access to this article as well as GBA’s complete library of premium articles and construction details. This article is only available to GBA Prime Members Start Free Trial Already a member? Log in