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Direct sympathomimetic catecholamines Mnemonic machine

Direct sympathomimetic catecholamines

Mnemonic: DINED
Dopamine
Isoproterenol
Norepinephrine
Epinephrine
Dobutamine

How Can direction of acceleration and velocity be parallel , anti parallel and perpendicular to each other

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Process of Transcription and translation of genetic code

Process of Transcription

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Process of Translation

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Killing for DNA: A predatory device in the cholera bacterium

Cholera is caused when the bacterium Vibrio cholerae infects the small intestine. The disease is characterized by acute watery diarrhea resulting in severe dehydration. EPFL scientists have now demonstrated that V. cholerae uses a tiny spear to stab and kill neighboring bacteria -- even of its own kind -- and then steal their DNA. This mechanism, known as "horizontal gene transfer," allows the cholera bacterium to become more virulent by absorbing the traits of its prey. The study is published in Science.

The lab of Melanie Blokesch at EPFL has uncovered how V. cholerae uses a predatory killing device to compete with surrounding bacteria and steal their DNA. This molecular killing device a spring-loaded spear that is constantly shooting out. This weapon is called the "type VI secretion system" (T6SS) and is known to exist in many types of bacteria. When V. cholerae comes close to other bacteria, the spear punches a hole into them, leaving them to die and release their genetic material, which the predator pulls into itself.

Killing neighbors and stealing genes

This spear-killing, predatory behavior is triggered by the bacterium's environment. The cholera bacterium naturally lives in water, such as the sea, where it attaches onto small planktonic crustaceans. There, it feeds on the main component of their shells: a sugar polymer called chitin. When chitin is available, V. cholerae goes into an aggressive survival mode called "natural competence." When in this mode, V. cholerae attacks neighboring bacteria with its spear -- even if they are of the same species.

Melanie Blokesch set out to explore how V. cholerae uses this behavior to compete for survival in nature. Her lab tested different strains of the bacterium from all over the world, most of which have been implicated in the 7th cholera pandemic, which began in Indonesia in the 1960's, spread rapidly to Asia, Europe, and Latin America, and still affects populations today.

The researchers grew these bacteria on chitin surfaces that simulated their natural habitat on crustaceans. What they found was that the tiny spear is not only part of V. cholerae's natural survival system, but it also contributed to the transfer of genes that could make the bacterium more resistant to threats, even to antibiotics. The researchers then used genetic and bioimaging techniques to identify, in real time, which mechanisms are involved in this event, which is called "horizontal gene transfer."

"Using this mode of DNA acquisition, a single V. cholerae cell can absorb fragments containing more than 40 genes from another bacterium," says Melanie Blokesch. "That's an enormous amount of new genetic information." This phenomenon is referred to as "horizontal" gene transfer, as opposed to the conventional "vertical" passage of genes from parent to offspring.

The importance of this study lies in the fact that horizontal gene transfer is a widespread phenomenon in bacteria, and it contributes to the dispersal of virulence factors and antibiotic resistances. In addition, the chitin-mediated activation of the spear-killing device most likely renders the bacterium more dangerous to patients when they ingest it, as this molecular spear might also kill protective bacteria in the human gut.

The researchers are now extending their investigation into the interplay between the chitin-induced production of the spear and horizontal gene transfer. "By studying this interplay, we can begin to better understand evolutionary forces that shape human pathogens and maybe also transmission of the disease cholera," says Blokesch.

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Materials provided by Ecole Polytechnique Fédérale de Lausanne. Note: Content may be edited for style and length.

New mechanism for Type IV pili retraction in Vibrio cholerae

Type IV pili, essential for many pathogens to cause disease, are hair-like appendages that grow out of and are retracted back into bacteria cells, enabling them to move and adhere to surfaces. Although pathogenic bacteria often rely on a specialized molecular motor to retract their pili, a new study in PLOS Pathogens reveals that a minor pilin protein elicits pilus retraction in the cholera bacterium, Vibrio cholerae.

Bacteria utilize a number of highly sophisticated molecular tools to colonize their hosts. One of the most ubiquitous is a complex nanomachine called the Type IV pilus. This nanomachine has as few as 10 to as many as 30 molecular components, producing exquisitely thin filaments that extend from the bacterial surface and that can be several times the length of the bacteria itself. These pilus filaments have a remarkable array of functions that rely on their ability to (i) adhere to many substrates, including host cell surfaces, pili from nearby bacteria, DNA and bacterial viruses (bacteriophage), and (ii) to depolymerize or retract, which pulls the bacteria along mucosal surfaces, pulls them close together in protective aggregates, and can even draw in substrates like DNA and bacteriophage for nutrition and genetic variation.

In collaboration with researchers from Dartmouth College and Simon Fraser University, Dr. Nicolas Biais, Assistant Professor of Biology at Brooklyn College, City University of New York (CUNY), developed an assay in his laboratory that revealed for the first time the V. cholerae Type IV pilus can retract without this molecular motor, and that retraction is necessary for these pili to function. Instead of a molecular motor, a small minor pilin protein triggers pilus retraction. "The magnitude of the forces though is much smaller," said Dr. Biais. "If Neisseria gonorrhoeae can pull roughly 100,000 times its bodyweight, Vibrio cholerae barely makes it to 1,000 times of its bodyweight. This is a new mechanism for retraction that will help understand how other pili and closely related secretion systems can work and potentially help with the design of novel antibiotics."

"This report [...] demonstrates that the bacterium that causes cholera powers a nanomachine required for infection differently than other disease causing bacteria," said Dr. Hank Seifert, Professor of Biomedical Sciences at Feinberg School of Medicine, Northwestern University, who was not involved with the study. "These findings drastically alter our understanding of how these nanomachines function to provide insights into the mechanisms allowing cholera and the development of synthetic nanomachines."

Research on how Type IV pili function not only advances our understanding of V. cholerae pathogenesis, but will also aid in developing future prevention and treatment strategies for cholera.

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Materials provided by The City University of New York. Note: Content may be edited for style and length.

How early should I start GMAT preparation?

Your GMAT score can be sent for 5 years, so I would recommend taking it as early as you are prepared, while you are still in school mode.

For those who are already out of school (the majority of GMAT takers), the answer depends on your mode of preparation and starting score.  If you don't know your starting score, take a practice test asap to get your baseline.

Self-studiers:
You'll want to allow at least 2 hours of self-study for every point you need to raise your score.  If you need 100 points, you'll want to allot 200 hours to be safe.  So if you're working full-time and can only devote ~10 hours of study per week, that's 4 or 5 months.  However, you will forget much of what you learned the first 2 months, so if you have more than 50 points to go, you'll want to do something different.

GMAT Class
Students who take GMAT classes don't do that much better than those who put the same amount of self-study in. The difference is on the order of 20 or 30 points.  I actually recommend hiring a private tutor for that amount of money.

Private Tutor
This of course depends on the tutor, but they should multiply your score increase rate by a factor of at least 2.  My students see their scores increase by between 3 and 7 points per tutoring hour (the fastest in the world). To get the most out of private tutoring, you will need to do homework between meetings and bring them only the questions you struggle with, so that you are not paying your tutor for things you could have done on your own.

Source: The World's Best Online GMAT Tutor