Thursday, November 28, 2019

History Of Cell Membrane Essays - Membrane Biology, Biology

History of Cell Membrane In the early stages of the twentieth century, little was known about cell membranes. Until the early 1950s, the biological cell membrane was rarely mentioned in scientific literature. It was recognised that something was probably there, but hardly anything about it was known. Considering the lack of technical equipment available a century ago, scientists such as Charles Overton and Edwin Gorter were not only exploring new territory in looking at the properties of cell membranes, but laying the way for future cell biologists. Scientists had to wait another fifty years for the discovery of the electron microscope, let alone seventy years for the advent of freeze fracturing techniques. Nageli and Cramer in 1855 had already suggested that biological cells are separated from their environment by a membrane possessing special characteristics, and in 1900 Overton performed some simple but classical experiments which proposed that cell membranes were composed of lipids (1). By measuring the permeability of various compounds across the membrane of a frog muscle, Overton found some interesting results. He observed that lipophilic molecules (molecules attracted to fat solvents) could easily cross this cell membrane, however larger lipid insoluble molecules could not. He also observed that small polar molecules could slowly cross the membrane. Other experiments with the likes of hen eggs suggested the presence of a lipid layer in the membrane. These results became known to biologists across the world and it was generally accepted that a semi-permeable lipid membrane surrounded some if not all cells (2). Although this was opening new doors for cell biologists, the information was widely disregarded. One hundred years ago biological fact was based on what could be seen and since the proposed lipid membrane was smaller than the wavelength of visible light it could not be studied under the light microscope. Most biologists merely concerned themselves with more evident structures. However, some scientists continued to dedicate their time to examining this invisible structure. Two such biologists were the Dutch Edwin Gorter and F. Grendel. They recognised in 1925 that two such lipid layers existed. Whilst working on red blood cells they showed the first detailed analysis of structure based on a new model. They extracted the lipid from a red blood cell and spread it as a film on water. The area covered by the lipid turned out to be twice the surface area of the red blood cell. Gorter and Grendel thus concluded that in a cell membrane phospholipids must be arranged as a bilayer, i.e. two lipid molecules thick (4).

Sunday, November 24, 2019

Computer Viruses and Hoaxes essays

Computer Viruses and Hoaxes essays Computer Viruses and Hoaxes: How To Protect Against Them There are over 30,000 known computer viruses and new viruses are being written every day. The number of computer hoaxes (lies) is not as high as the number of viruses, but for the many computer users, who may believe the false information, hoaxes can cause them a lot of emotion and wasted time. The hoaxes are annoying but, if the user can recognize them, can be easily deleted. It is the threat of a computer virus that is the most important to a user because no system is immune to a virus infection. There are methods for detecting a virus, eliminating it and protecting the system from further trouble. A computer virus is a piece of software designed to enter a system and infect the files. A virus will duplicate itself and try to infect as many files and systems as possible. If the hard disc is infected and the user saves a file to disk, it will probably infect the disk and will be passed on to other systems that use the infected disc. On the other way, if a virus-infected disk is introduced to the system, it will infect the system. (What Is A Virus? 1) There are four main types of computer viruses; boot sector, file or program, macro, and multipartite. The boot sector viruses are usually transmitted by an infected floppy disk that is left in the disc drive and then the system is rebooted. The virus is then read from the floppy to the master boot record of the hard drive and when the computer is booted up, the virus goes into the systems memory. (Types Of Viruses 1) File or program viruses are pieces of viral code that attach themselves to executable programs. Once the infected program is run, the virus is transferred to your systems memory and may replicate itself further (Types of Viruses 1). The macro viruses are the most common because they infect files run by applications that use macro languages (Microsoft Word or E...

Thursday, November 21, 2019

Economic Value Added Assignment Example | Topics and Well Written Essays - 500 words

Economic Value Added - Assignment Example There are two main types of financing for a business, debt and equity financing. When accountants calculate net income, they deduct the interest expense (which is the cost of the debt capital). However, the cost of the equity is not taken into account. Therefore, the net income exaggerates the ‘true’ net income in economic terms. This flaw is overcome by the EVA method. A positive EVA indicates that value is being created i.e. value of the company increases by that amount. On the other hand, a negative EVA indicates that value is decreased and the company is now worth less than the initial capital employed (which is the assets from which earnings for the year are generated). (Russell) A value of zero means a sufficient achievement because shareholders have earned a return that just compensates for their risk. The term â€Å"Operating Capital† used in the EVA formula on the last page accounts for the interest-bearing debt, preferred and the common stock used to acquire the company’s net operating assets. In easy terms, it is the capital which was used to acquire net plant and equipment plus the net current assets. EVA = (Operating capital) * (ROIC – WACC) i.e. a firm adds value if it’s ROIC – Return on Invested Capital is greater than the WACC – Weighted average Cost of Capital. However, if WACC goes beyond the ROIC, then new investments in the operating capital will actually reduce the firm’s value. EVA is an estimate of a business’s true economic profit for the year, and if differs sharply for accounting profit. Accounting profit is basically determined without imposing any charge for the cost of equity capital and is therefore an overstatement in economic terms. However, EVA determines the residual income after accounting for all the cost of capital (debt and equity both) and provides a much better performance measure to the stakeholders. Misra, Anil and Kanwal Anil. "Economic Value Added (EVA) as the most