Cherished Love Essay Example | Topics and Well Written Essays - 750 words

Cherished Love - Essay Example He was taking the information so deeply it seemed my decision was so abrupt. I always told him about it before, preparing him for such a time as this as I knew pretty well that my departure is inevitable. My mother is in the United States and she wanted me to join her because things are really tough for us in Poland. My boyfriend said he was afraid I would stop loving him. Of course this was foolish. I know deep in my heart that I would always cherish him, adore and regard him with deep love and fidelity. I understood how he felt. I feel the same way however, I kept it unspoken. The atmosphere was so tense between us especially when he got testy, finding how I might take things if some unexpected events happened. To all his questions I said I will always remain loving him. How would I forget such a wonderful man? He was always romantic, always ready with something new to spice up our relationship. Expecting a surprise from him would never stop me from being surprised. He was just so witty, bright and fantastic. There never seemed to be a boring moment spent with him. He was always thoughtful. One of the treasures I brought along with me is a couple of brown bunnies my boyfriend gave me. He knew how I love animals and he just thought I might want to have something that would last for years, something that would not die, â€Å"like our love†, he said. That was so sweet of him and I treasure such memories. I find my boyfriend a wonderful man who is just so full of equally wonderful ideas to express how he felt towards me. This made me always feel comfortable with him even in the presence of his parents or friends. I knew I was genuinely loved and I in return, gave my generous love that seemed to have known no bounds. My days would always be fantastic after spending time with him, sharing a lazy moment when we did nothing but talk, laugh and enjoy each other’s company. He is a true debonair, I must say. He sure is the sunshine in my life, bringing che er to my gloomy days and encouragement when I am down. He is always energetic I always wonder where he finds all the strength to be so active in school and at home and yet would find much time to nurture the relationship that we shared. He is also funny and sometimes, he would go to an extreme and could almost be hilarious. There are also days that he would just simply be silly but not the kind of silly that is laughable. He sometimes just expresses himself weirdly like for instance, we are walking and he suddenly kneels in front of me to sing a song of love. I find that stupid and silly especially when he does that in front of other people but I guess that is how love would drive a person to madly indulge in. I consider my boyfriend mature and reflective. When he talks, he makes a lot of sense one would think he is speaking to a philosopher. He is a dreamer and in his plans and objectives, he always considers me. We were still teenagers then, and I think for a man to have such clea r perceptions of his future at such age, there is a certain maturity that is almost unseen from most of our age mates. He was always sincere with his words, expressing his love when he is at the summit of his emotions and saying just how bad he felt when something bad hit him. This is one of the attributes that has attracted me to my boyfriend because I find that in our world today, men who show their manliness through muscles and good looks and probably a string of women they attach to their character. However for me, I am more interested in the attitude than the physical attributes. He is also kind-hearted and sensitive. Sensitivity might be more appropriate for women, thought of as a feminine attribute yet, I find it attractive to be on a man especially

My Philosophy of Education Essay Example | Topics and Well Written Essays - 750 words

My Philosophy of Education - Essay Example From the video clip, the children learn by touching, seeing and feeling the concepts in the use of beads in understanding math. The child gets comfortable with all the materials that represent certain symbols. They can count the symbols from 0-9 by binding the spindle by a rubber band, to represent symbols. This is aimed at helping them manipulate numbers of any magnitude. Pestalozzian and Montessorian teaching techniques included the use of a special environment for learning, by using materials and activities that are based on the conservation of the children. Contrary to the conventional schools, children are not motivated to learn by rewards and subjected to punishments if they fail. Here children learn at their will. They concentrate on structure and play with objects, repeat the previous actions until they master a specific skill. Their capacity for learning lead to reading and writing skills on their own will. Ms. Williams used the same techniques as Pestalozzian and Montessorian. She gave children materials like small sticks and beads to play with. They tie the objects in the representation of symbols. They learn the concept of numbers and understand math. This is because children like playing with objects and enjoy touching everything. They learn by touching, feeling and gaining skills from it. Same as Pestalozzian and Montessorian, they are no t motivated by rewards. They learn at their convenience. Ms. Williams gives objects to children to learn by touching and playing with them. They acquire skills not by being told but by touching, seeing and understanding how everything works. For instance, a cat can scratch when handled carelessly, instead of telling them, they will experience it. So they will be careful next time, because they touched the cat, and learned how to handle it; where to touch it and where to avoid. That’s a skill they have learned through their own initiative.

Around the World Essay Example | Topics and Well Written Essays - 1000 words

Around the World - Essay Example Channel Access: Access of the alliance company to the various channels required for the business. Local Laws: Local laws with respect to formation of alliances need to be considered. Competency and Value of the Alliance Company: Competency of the alliance company and the value that it adds to the alliance is key to a successful alliance. The alliance must take the form of an international joint venture. International joint venture is an economically and legally separate organizational entity that has been created by 2 or more parent organizations with the objective to achieve strategic objectives. Parent companies invest both financial and other resources at disposal into the alliance (Schuler et al., 2004). A joint venture alliance has various advantages and is best suited in the current case. The major challenges for Around the World in establishing an international joint venture is shareholdings, human resource management, skills sharing and knowledge transfers. These challenges c an be overcome by effective and early planning. Share holdings and control structures of the partners need to be established and agreed upon before the alliance materializes. There are various ways to effectively manage the HR issues and, the knowledge and skill management issues. A four stage model of formation, development, implementation and advancement can be used to effectively to handle the challenges (Schuler & Tarique, 2004). Case Study 2 Following are the discussion points for the three questions at the end of the case study: 1. Aditya Birla Group adopted a growth strategy that made great business sense. The group exited from any business that did not offer them greater presence in the global market or the business which had registered losses. The group diversified and adopted businesses whose operations gave the group global presence and lead to acquiring of competencies in the market. The company built a business portfolio which is not limited to a single industry. The po rtfolio demonstrates the group’s ability to run different businesses efficiently and also has contributed to various revenue generating sources which has made the group immune to economic downturn in certain market or industries. 2. Various initiatives were taken by the group under the leadership of Kumar Mangalam Birla which has contributed to the group’s success. Gyanodaya was a great initiative which helped in the transfer of best practices. Appointment of new managers gave rise to a new dimension in the group’s leadership. Continuous learning and developing of human resources was one of main motive behind many of the initiatives. 3. Aditya Birla Group has addressed its second part of the mission – â€Å"Indian Values† by actively involving and contributing to the development of the country. It is presently working in 3700 villages. It is concentrating on health care, sustainable livelihood, infrastructure, education, social causes, etc through its Aditya Birla Centre for Community Initiatives and Rural Development. It is running around 18 hospitals and 14 schools. Case Study 3 In order for Aston Restaurant to extend their business to China, they have to consider various factors and the two important factors are the market and the localization. Market No two markets are same and there are numerous differences that have to be looked into. The following various issues/factors have to be addressed or considered for Aston to successfully expand to China: Language: Language is a primary barrier here and Aston has to ensure that language i.e., communication must not hinder the business. Chinese is the primary language used in China. Customs and Practices: The customs and practices in China are different from those in other countries. In

Sociological Analysis of the Crucible Essay Example for Free

Sociological Analysis of the Crucible Essay Sometimes, the person who should be the one wielding the power has none at all. In Arthur Miller’s play, The Crucible, he recounts the events of the Salem Witch Trials. As he tells the events that occurred, he clearly paints out who held the power and who should have been in power during the trials. In Miller’s play, the person who holds the most power in Salem during the Witch Trials is Abigail Williams. Despite being a child and an orphan, for her parents had died and she was sent to live her uncle Mr. Parris, she was able to gain unlimited power during this short span of time. When Mr. Parris caught her and other local girls out dancing at night, she threatened the others, â€Å"Let either of you breathe a word, or the edge of a word, about the other things, or I will come to you in the black of some terrible night†¦Ã¢â‚¬  (20), and they listened to her. None of the girls would speak against Abigail, and when Mary Warren did, the other girls did not join Mary; they protected Abigail and listened to her every word. As the play goes on, Abigail gains more and more power, accusing people in the town as witches. At the end of Act 1, Abigail cries out to Reverend Hale, â€Å"I want the light of God†¦ I saw Sarah Good with the Devil! I saw Goody Osburn with the Devil!†(48). Unfortunately for the accused, they were arrested and were tried by Judge Danforth, and were found to be guilty of witchcraft. Abigail becomes a saint in Salem, saving the villagers from the witches; however, little do they know, Abigail is using her newfound power for her own good. When she accuses Goody Proctor of being a witch, no one questions her; Abigail is helping the town out. But, the reason she accuses Goody Proctor is because Abigail secretly wants to be with John Proctor, Goody Proctor’s husband. When John Proctor defends his wife in court, he confesses to adultery with Abigail, and tells them that is why Abigail accused Goody Proctor in the first place. John Proctor tells Judge Danforth, â€Å"But it is a whore’s vengeance†¦ she thinks to dance with me on my wife’s grave!à ¢â‚¬ (110). Nether less, Abigail has power that John Proctor does not, she can ‘see’ the Devil, and Danforth believes her. Abigail Williams has the power in Salem, though she does not deserve it. Though Abigail has authority in Salem, the one who really deserves the power is John Proctor. Throughout the whole affair, Proctor is the only one who knows what is right and what is wrong. When Mr. Cheever comes to Proctor’s house to collect his wife, Goody Proctor, Proctor tells them, â€Å"Is the accuser always holy now? We are what we always were in Salem, but now the little crazy children are dangling the keys of the kingdom, and common vengeance writes the law!†(77). Proctor accurately sums up the situation in Salem, yet no one with any real power believes him, and they all discount him. Later on in the play, Proctor tells Judge Danforth, â€Å"I believe she means to murder,† (104). John Proctor was trying to tell the Judge that Abigail really was a bad person, not the saint she was painted out to be. But, Judge Danforth was under Abigail’s spell, and didn’t listen to John Proctor, even though he was the only person who actually was thinking clearly during this whole situation. John Proctor was the only who kept clear head during the Salem Witch Trials, and if he had held the power, not Abigail, things would have changed drastically. In The Crucible, by Arthur Miller, the events of the Salem Witch Trials are recounted. As the play continues, Miller accurately shows who has the power and who should have had the power. Abigail Williams, despite being an orphan, was hailed as a saint and everyone listened to what she said; however, she was a liar and a whore. John Proctor, who was accused of being a witch and was never listened to, had a clear head and understood what was happening unlike the other villagers. The Salem Witch Trials could have been avoided if the power had been taken out of Abigail’s hand and given to John.

The object of grammar Essay Example for Free

The object of grammar Essay Two types of grammar: normative, theoretical. Two parts of grammar: morphology, syntax. Grammar is a branch of Linguistics which studies the grammatical structure of language. The grammatical structure covers the rules of changing words and rules of arranging the forms of words into phrases and sentences. Grammar may study the gr. Structure of a language in different aspects. So? We distinguish: historical grammar which describes the str. of words, phrases, sentences in the process of their historical development; comparative gr. which deals with comparison of gr. systems of different languages; descriptive gr. analyses the gr. system of a language as it exists at a certain period of time. Grammar is divided into 2 types: Normative and Theoretical. Normative (Practical) Grammar gives rules how to build correct forms of words and syntactical constructions. It teaches to write and speak correctly. Theoretical (Scientific) Grammar describes the language as a system, studies the components of that system and relations between them. Theoretical gr. explains and analyses the most difficult phenomena of a language. It gives different concepts of these phenomena and helps linguists to be guided in linguistic literature in order to form a certain opinion of this or that theoretical form. Grammar is divided also into 2 parts: Morphology and Syntax. Morphology is a part of Grammar which studies the most characteristic features of classes of words. These classes are called parts of speech. Morphology studies not a single word, but the whole classes. Syntax is a part of Grammar which studies phrases and sentences, their structure, classification and combinations. Syntax is a system of 2 levels-that of phrases, that of sentences. It may be said that, in a way, morphology is more abstract than syntax, as it does not study connections between words actually used together in sentences, but connections between forms actually found in different sentences. In another way, however, morphology would appear to be less abstract than syntax, as it studies units of a smaller and more compact kind, whereas syntax deals with larger units, whose types and varieties are hard to number.

High Throughput Screening (HTS) Assays: Uses and Formats

High Throughput Screening (HTS) Assays: Uses and Formats The increasing demands placed upon the pharmaceutical industry to produce a rapid turnaround of new drugs is a driving factor in the automation of the processes at the initial screening stage of drug discovery. This has lead to the development of numerous high throughput screening (HTS) assays, with the increasing miniaturization of the whole process (1). An explosion in genomic and proteomic studies in recent decades has lead to the generation of large numbers of functional protein molecules. The physiological function of these proteins has yet to be elucidated, but many could be important future drug targets, such as receptors or enzymes involved in disease pathogenesis (2). These ‘orphan receptors’ can be studied by high throughput screens of small molecules, which may be potential ligands. These chemicals can be sourced from existing drugs, pharmaceutical company chemical compound libraries or from natural products, such as plants or animals (figure 1; 3). Chemical l ibraries are now vast, since the advent of combinatorial chemistry, which produces novel compounds by high throughput methods. These mixtures can then be assessed for biological activity against a specific target molecule (most commonly a protein), either as a mixed chemical pool, or in parallel. A positive/active interaction, or ‘hit’, can then be further explored. Numerous assay detection formats that are suitable for automation have been developed to detect such receptor – ligand and enzyme – substrate interactions, to allow the potential drug molecule to be further explored. Each assay has advantages and problems and the most commonly applied techniques are discussed in this review. As research progresses these processes become modified to overcome problems created by the progressive automation and miniaturization of the assays. Use of computation to analyse the interactions and extract more information from them is also increasing (4). Recent advances in the literature suggest that future development of HTS is likely to result in ultra-HTS assay formats, which may be within closed systems such as glass capillaries, or on silicon wafer chips. References Fonseca MH List B (2004) Curr Opin Chem Biol, 8, 319-326. Gilchrist A (2004) Expert Opin Ther Targets, 8, 495-8. Bleicher KH, Bohm HJ, Muller K, Alanine AI (2003) Nat Rev Drug Disc 2, 369-378. Kato R, Nakano H, Konishi H, Kato K, Koga Y et al. (2005) J Mol Biol, 351, 683-92. Techniques in molecular biology, chemistry and their associated branches are advancing at a rapid rate. This has enabled the mechanisms underlying many diseases to be explored at the molecular level. The ever-increasing sophistication of proteomic and genomic research procedures are producing an explosion in the number of possible drug targets. Until the development of high throughput screening (HTS) assays, the time taken to evaluate the potential bioactivity and usefulness of compounds to act on target molecules and become drugs to act to ameliorate symptoms or even cure or prevent a disease from occurring, was a rate-limiting factor. Since the automation of a number of suitable assays for HTS the trend has led to the number of compounds available for testing against targets becoming the limiting factor. This has spurned the growth of combinatorial chemistry, to such an extent that many consider it to be a branch of chemistry in itself. HTS can be defined as an automated method of conducting a large number of in vitro assays on a small scale (Patrick 2005). Most commonly, 96-well plates of 0.1ml are used for a number of bioassays to detect the biological activity of compounds which have the potential to be developed as drugs. These may interact with the target, as a ligand-receptor interaction, or may involve inhibition of an enzyme or interaction with a nucleic acid macromolecule. The reaction produces a detectable output change, which can be detected and/or measured. Thousands of chemicals can easily and quickly be screened this way, and only active compounds taken to the next stage of testing to find out if it has the potential to become marketed as a drug. There is increasing pressure on drug companies to produce new drugs to keep pace with developments in medical research, as well as an increasingly demanding public and share holders. HTS technology is a crucial to meeting these demands, and continues to be dev eloped to produce faster, cheaper and more efficient ways of screening compounds during the initial stages of the drug discovery process. ROLE OF HIGH THROUGHPUT SCREENING IN DRUG SCREENING Molecular biology techniques are allowing us to understand more about the mechanisms of disease, thus providing biomacromolecular targets for potential drugs to interact with. Such targets include receptors, enzymes and nucleic acids and may require inhibition (enzymes) or agonistic/antagonist receptor ligand binding to produce the desired pharmaceutical effect. In addition, studies using proteomic and genomic techniques are revealing more and more ‘orphan receptors’; these are proteins (predominately), lipids and nucleic acids (and to some extent carbohydrates) that are now known to be produced by the body, but their messenger and function is unknown. Using these as targets against which to screen compounds will help to elucidate their function, and more importantly, may turn out to be drug target interaction sites which will be beneficial in disease. As the function of these targets is unknown, there are no lead compounds that could be used as a starting point for exploration, so HTS is particularly beneficial for screening vast numbers of compounds in the hope that at least one will interact with the mystery target. The number of potential drugs to be screened is vast; pharmaceutical companies have libraries of 0.5-2 million synthetic compounds (King 2002) that have not made it through screening to become marketed drugs. There are also commercially available libraries of compounds, such as the Chemical Abstract Service (CAS) registry file, which contains 39 million compound (Abraham 2003). Intermediates in synthetic processes to make another drug should also be screened, as they may have the desired pharmaceutical properties. Isoniazid is an intermediate and has now been developed into an effective anti-tuberculosis drug. Existing drugs are also worth screening, as their biological activity may stretch beyond that for which they are intended. For example, cyclosporin A was isolated from soil and had been intended for use as an antibiotic, until its immune-suppressive properties were observed and for which it is now sold. The body’s own endogenous chemical messengers, such as morphine, whi ch has similar activity to released endorphins, could also be screened as they may provide a lead compound that can be modified to enhance activity. Combinatorial synthetic processes can also be used to generate vast numbers of novel compounds, which is crucial to prevent the availability of new compounds being a limiting factor in drug development, as HTS is able to screen them so quickly (Carell et al. 1995). It is common for combinatorial synthesis to produce mixtures of compounds, which can be tested as a chemical pool or batch by HTS for biological activity against a specific target macromolecule. This means that thousands of compounds can be screened in a very short time and only pools containing biologically active constituents screened further. This usually involves deconvolution processes (such as micromanipulation, recursive deconvolution or sequential release from resin beads used for the synthetic process) to identify exactly which component(s) of the pool is/are active, so that they can be isolated and screened further for drug potential (Wilson-Lingardo et al. 1996). It is now being superseded by production of new c ompounds in parallel, with a single component in each well. Potential drug molecules can also be derived from natural sources, such as plant extracts, but these are less abundant as isolation and purification take time. They are often novel, complex molecules and can produce unexpected interactions. An example is artemisinin, an effective antimalarial drug developed from extracts from a Chinese plant; it has a highly unstable trioxane ring (Ploypradith 2004). There are so many compounds to be tested against a large range of potential drug targets that high throughput methods are essential to test the numerable combinations of drug and target interaction to find those that are biologically compatible. HIGH THROUGHPUT SCREENING ASSAYS In theory any assay that can be performed on the laboratory bench could be automated and scaled up to be used for HTS. In practice, however, some assays are intrinsically more suitable than others. High throughput screens require the automation of the entire process. This is best achieved if there are as few steps as possible in the assay; ideally the test should be able to be performed in a single well, with addition of the test sample the last key step. Obviously, it is important that the reaction between a target and biologically active compound must be readily detectable. It should ideally be detectable with high sensitivity while the products are still mixed together in the well, rather than needing further steps to separate or purify components of the reaction mixture. This can be difficult to achieve with automation and will increase the time taken per test, so becoming less efficient and cost effective. Assays used for chemical screening can be cell-free or cell-based (Silverman et al. 1998). Cell-free assays use solutions of relatively pure protein targets, such as receptors or enzyme substrates, which minimizes the number of steps required. It also allows for easy detection of biological activity in the wells of reaction mixture. Cell-based assays have the advantage that they are a closer representation of the normal physiology of the chemical environment inside a cell. Receptor-ligand interactions and enzyme inhibition reactions are more likely to be indicative of what will happen in vivo (Silverman et al. 1998), especially if ligand-gated ion channels are involved. Cell assays also allow specific processes to be studied and the output can be measured. Indirect effects of small molecule/protein binding which trigger secondary messenger systems, such as calcium ions or cAMP, can also be observed in their biological context. Cells can be manipulated to express target molecules on t he surface, so that they are available to bind to novel ligands, which may be tagged for detection. Cell assays can also provide additional information about cytotoxicity and bioavailability of a potential drug. Mammalian cells are expensive and can be difficult to culture in automated HT systems, but yeasts can provide a suitable alternative. Microorganisms such as yeasts are easy to propagate and have been demonstrated to have some homologous chemical processes, or can be easily genetically modified to express human processes accurately (Klein Geary 1997). HTS ASSAYS AND DETECTION FORMATS Fluorescence Fluorescence occurs when a fluorophore molecule absorbs a high-energy photon (often in the ultraviolet range) and emits a lower energy photon, which is typically in the visible range of the spectrum. There are many naturally occurring substances which have this intrinsic property, such as luciferin in fire-flies. There are a number of fluorescence – based assays available for use in HTS, to detect whether an interaction has occurred between target and potential drug molecule during random screening. Fluorescence assays are generally sensitive, versatile, stable, safe and easy to perform, which gives them a great advantage in automated systems for HTS. They have the disadvantage that quenchers can be present in the sample which dampen the light emission. There may also be background autofluorescence from free reagents in the reaction mixture (Grepin Pernelle 2000). Many of the assays have developed protocols that take these problems into account. Energy transfer formats: Homogeneous time resolved fluorescence (HTRF) uses the ion of the rare earth metal lanthamide (Eu3+ ), bound to crypate as a donor molecule. Following laser excitation (at a wavelength of 337nm), energy is transferred from this complex to an allophyocyanin (APC) acceptor molecule. This results in emission of light of 665nm, over a long period (milliseconds), which is recorded in a time resolved fashion so that any background fluorescence from free APC or media is not recorded. Peak emission of light occurs at 620nm for unbound Eu-cryptate, so the ratio of 620:665nm emissions can be used to quantify biological complexes in solution (see Figure 1). This technique can be widely applied to screening programs and has already been developed into a 1,536 well plate HTS, with plans to expand this to become ultra HTS (uHTS) and for use in cell-based assays. Figure 1: HRTF schematic explanation (from: Grepin Pernelle 2000) Fluorescence resonance energy transfer (FRET) is a slightly different form of detection, using the principle that excitation energy can be transferred between two fluorophore molecules. These can be different types of green fluorescent protein (GFP) or other bioluminescent molecules, such as luciferase (Hu et al. 2005). from: Becker et al. 2004 Fluorescence polarization (FP) FP can be used as the basis for homogeneous HTS assays for enzymatic and ligand-receptor binding interactions. The principle behind this detection assay is that when polarized light hits a small molecule that is binding to a larger (target) molecule, there will be rotational diffusion of the light beam. This change induced by binding can be detected by measuring the light emitted in orthogonal and normal planes of the polarized light. There is no interference from absorptive compounds in complex mixtures, as can occur with other fluorescence based techniques, and FP is quick and easy. Because of this it is used widely in high-throughput screening systems. Kim and colleagues (2004) developed a FP assay for the molecular chaperone Hsp90 (heat-shock protein), which is believed to have a role in cancer. They validated the assay for a high throughput format using molecules known to bind Hsp90, such as geldanamycin. The assay can now be used to screen for novel inhibitors of Hsp90, which m ay lead to a cancer drug being developed. Stricher and others (2005) have developed a high throughput FP assay for the CD4 binding site of HIV-1 glcoproteins, such as gp120, which are crucial targets to protect against HIV infection. Their assay used a 384-well plate and CD4M33, a mimic of host cell receptor antigen CD4, found on T helper lymphocytes. Some studies indicate that FP assay technology can also be developed as part of a HT structure-activity (SAR) study. Newman Josiah (2004) showed that FP is sufficiently sensitive to differentiate between high-affinity small molecule inhibitors interacting with the target and low-affinity ones, with Src kinase activity as a model. FP can also be used in cell-based assays, in conjunction with confocal microscopy (Heilker et al. 2005), as it shows high sensitivity even at minute volumes of reaction mixture, down to femtolitres. This type of assay can be described as fluorescence intensity distribution anaylsis (FIDA) and measures the absolute concentration of both bound and unbound ligand, thus providing the data with its own internal control. FIDA has been used to explore ligands which bind to G-protein coupled receptors (GPCR), which are widespread throughout the body and involved in signal transduction for numerous cell processes. They are therefore important therapeutic pharmaceutical targets, and can be studied in association with membrane fragments from cells over-expressing GPCR or associated with virus-like particles. Fluorescence correlation spectroscopy (FCS) FCS uses a two-photon excitation to measure the relative fluorescence of different molecules within a homogeneous mixture, from which the amount of each can be calculated. The technique can be applied to measure the relative amounts of ligand bound versus unbound receptor molecules, or cleaved versus intact enzyme substrates. FCS can be conducted using minute reaction volumes, less than 1 femtolitre (fl) is adequate for this sensitive, fast assay, which can study interactions of single molecules (Sterrer Henco 1997). FCS can also be used to study ligand-receptor interactions in live cells (Pramanik 2004), which allows reactions to be assessed, and to some extent the properties of the interaction quantified, in their biological context. The use of such live cell assays in a high throughput format will provide a wealth of information not observable in chemical solutions alone. Many applications of FCS are conducted in conjunction with confocal microscopy, which allows interaction kinetics to be examined on a molecular level, by the changes in diffusion patterns of the excitation. Confocal microscopy uses a high numerical aperture lens to focus the laser, to provide excitation and produces minimal background excitation, which allows such minute quantities to be studied. It can be used to detect spatial and temporal interactions in live cells, increasing the amount of information that can be obtained and used for drug development (such as interactions with other cell components or pH effects within the cell; Zemanova et al. 2003) The dual-colour cross- correlation spectroscopy method of FCS uses two different, spectrally separated, fluorophore molecules, which are attached to each of, for example, a receptor and possible ligand, or potential substrate to be cleaved. The two colours will be observed to fluoresce together if an interaction occurs, or separately if a substrate has been cleaved and the kinetics of this can then be assessed (Kettling et al. 1998). This can be demonstrated using, a DNA strand that has a red fluorophore molecule attached to one and and a green one to the opposing end. The strand is cleaved by restriction endonuclease enzyme ecoRI, which is detected by spectroscopy as a decrease in the quantity of DNA molecules with fluorescence at both ends. The method was shown to be suitable for this type of enzyme kinetics study, by accurate detection of catalytic activity down to an enzyme concentration of 1 pM (pico molar) and proper description of the reaction by the Michaelis-Menten equation. This method, dual-colour FCCS, therefore has great potential for HTS of enzyme and ligand binding reactions. Biomolecular fluorescence/reporters There are numerous molecules produced by plants and animals naturally that produce fluorescence, or what is sometimes called bioluminescence. Some of these have been adopted as research tools, such as green fluorescent protein (GFP), which produces green light at 509nm following excitation by blue light (Arun et al. 2005). The gene that encodes for this fluorescent protein has been elucidated and is now commonly inserted into the genomes of genetically modified microrganisms and cell lines. It is then expressed under the control of desired promoters, often as a fusion protein. In this way patterns of gene expression can be observed and changes in transcription detected. HTS for new drugs use this technology to detect changes in transcription that occur via secondary messenger systems following receptor-ligand binding in a live cell. For example, Changsen and others have validated a GPF microplate assay, using an acetamidase promoter associated with the gfp gene, to screen for antitub erculosis drugs (2003), and found it to be suitable for HTS for novel drugs. GFP reporter technology requires a detection system and most of those described for detecting fluorescence from synthetic fluorophores can also be applied, such as FRET (Zhang 2004), FCS and confocal microscopy. FITC (fluorescein – 5- isothiocyanate) FITC can be bound to other molecules as a marker and the fluorescence measured robotically in HTS systems. For example, FITC bound to heparin sulphate (HS) has been used to screen for heparanase inhibitors in a HT assay: 384-well microtitre plates are used, which are coated with fibroblast growth factor (FGF). This captures the FITC-HS, and labelled fragments are only released into the media when cleavage by heparanase has occurred. This is quantitatively measured by robotic detection of the amount of fluorescence in solution. Heparanase is believed to have roles in inflammation, tumour angiogenesis and metastasis, so is an important drug target in the treatment of cancer (Huang et al. 2004). Chemiluminescence Some assays using chemiluminescence have been adapted to use HT formats. These rely on chemical reactions to produce light emission as a side-product, which can be detected. One such HTS uses coupled reactions involving the enzymes acetylcholinesterase, choline oxidase and horse-radish peroxidase, in 96 and 384-well plate formats, to screen for novel acetylcholinesterase inhibitors to become new drugs to treat Alzheimer’s Disease (Andreani et al. 2005). Scintillation proximity assay (SPA) Scintillation proximity assays are used for quantitatively studying binding reactions. The receptor/target is bound to a surface such as a plastic bead. The ligand is labelled with radioactive isotype (typically H3 or I125 ) and emit electrons with a short range of about 10um. A scintillation counter under the surface to which the target is bound detects the ligand only when it is bound. When it is free in solution the media absorbs the electrons and they are not counted. This allows binding interactions to be quantified whilst at equilibrium. Zheng and others (2004) have used SPA as part of a HTS and have identified several novel inositol monophosphatase inhibitors, which may be developed as drugs fro bipolar disorder. Mass spectrometry Mass spectrometry is currently a popular option for HTS, as it is sensitive, selective and easily automated. It allows the activity, molecular weight (most drug-like molecules are 150-400 Da), elemental composition and structural features of a test compound to be analysed. This wealth of information is of great use for exploring the molecular interactions between target and potential drug compounds. A very high throughput can be achieved using flow injection analysis, which does not require any sample preparation. Solutions of the samples are sprayed, using electrospray or APCI (atmospheric pressure chemical ionization), which ionises the molecules in the sample, prior to analysis by the mass spectrometer. Sometimes tandem mass spectrometers are employed, to glean more structural information and elemental composition. The advantage of these techniques are that as well as being very high precision they can be conducted on the original sample, without the need the separate the compound out from a mixture. For LC-MS (liquid chromatography mass spectrometry), semipreparative HPLC (High Peformance Liquid Chromatography) is often used before the HTS to verify the structure and purity of each compound to be tested, especially those from a combinatorial library. Improving purity in this way facilitates more accurate observation of any biological interactions that occur between the target and the test compound, as well as easing interpretation of structural information about the test molecule or changes induced by the interaction (Abraham 2003). HPLC is easily automated and involves detection of a UV signal above a threshold level, which triggers collection of the fraction. Several fractions may be obtained from one sample, or the computers controlling sample collection can be programmed to detect only at peaks of desired molecular ions, following ionisation by a suitable technique, such as electrospray or MALDI (matrix-associated laser desorption/ionisation), which can be used as a gentle way of ionising more fragile molecules (Hillenkamp et al. 1991). LC-MS can be slower than other approaches but is sometimes necessary. Further developments to speed up the automated process include parallel LC-MS, in which multiple HPLC columns are interfaced to a single mass spectrometer (Kenseth Coldiron 2004), and fast HPLC. NMR NMR is a useful technique for exploring the 3-dimensional structure of biomacromolecules, in a concentrated solution. It is limited by the small size of molecule amenable to this technique; typically below 30kDa, so is more useful for small drug-like molecules than the molecular target they interact with. Structure-activity relationships (SAR) can be studied by observing alterations in a protein’s NMR spectrum. This not only indicates that ligand binding has occurred, but can give an indication of the location of the binding site (Shuker et al. 1996). X-ray crystallography X-ray crystallography enables the 3-dimensional structure of protein molecules to be studied, with resolution to the atomic level. The technique requires the molecule to be studied in its crystalline form, which is not a problem for the majority of biomacromolecules that are drug targets. Protein crystallization technology has also had to adapt to high throughput methods, so as not to become a bottleneck. Some fully automated systems can now produce as many as 2,500 to 140,000 crystallization experiments a day (Kuhn et al. 2002). Studying the 3-D structure of the target often produces clues to the type of ligand that will bind, which speeds up the time taken to find lead compounds in drug discovery. An example of this is the development of antiretroviral drugs used to treat AIDS (acquired immunodeficiency syndrome), such as amprenavir (‘Agenerase’), which followed from the study of the structure of the drug target, HIV (human immunodeficiency virus) viral protease. Another drug developed from such structure based studies is zanamivir (‘Relenza’); a flu treatment based on the crystal structure of the surface glycoprotein, neuraminidase, which is crucial for viral infectivity (Varghese 1998). This is likely to be an important weapon in the fight against an influenza pandemic. In X-ray crystallography, the macromolecular 3-D crystal is bombarded with X-rays, by a rotating-anode X-ray generator or a synchrotron, and the diffraction pattern produced is detected. Multiple measurements of diffracted waves generate much data, which can be analysed using calculations, such as Fourier synthesis and a structure revealed (Blundell et al. 2002). Advances in the structure determination process have aided the resolution of structures, for example, multiple-wavelength anomalous dispersion (MAD), in which selenomethionine is incorporated into proteins that are overexpressed by genetically modified micro-organisms, which simulates isomorphous replacement and allows the phases to be calculated (Hendrickson et al. 1990). Low-affinity binding reactions between ligand and target may have important properties and provide leads that would be missed by other HTS methods. Development of high throughput X-ray crystallography, by increased automation at all stages of the procedure, has lead to its growing use in lead discovery as well as its more traditional role in lead optimisation (Abola et al. 2000). This enables the technique to screen compound libraries, including those from combinatorial synthesis. Crystallographic screening for novel ligands in this way has already had some success; for example, a new class of urokinase inhibitors have been discovered, for treating cancer (Nienaber et al. 2000). Co-crystallization of receptor-ligand complexes allows the interaction between the molecules to be studied and conformational changes in the target, upon binding, to be discovered. This approach is known to be used by several industrial laboratories and has the capacity to compare the interactions of ‘hit’ ligands in the generation of a lead series. It also decreases the time taken to explore hits, which is a crucial factor for the pharmaceutical industry (Abraham 2003). Another way of achieving crystallized receptor-ligand interactions is to soak the ligand, often as molecular fragments dissolved in DMSO (dimethyl sulphoxide), into the receptor protein crystal (Nienaber et al. 2000), and observe changes in electron densities indicative of interaction. Structure based drug design in silico Three-dimensional structures can also be used in computer modelling programs to predict which ligands might bond/interact with targets or receptors, as an initial stage of drug design. This is truly a high throughput method as computing power allows the rate at which ligand-receptor interactions can be virtually screened to be incomparable to even the fastest high throughput methods involving physical experimentation. This is often termed virtual ligand screening (VLS), or in silico screening (Klebe 2000). Perrakis and his colleagues (1999) combined automated protein model building with iterative structure refinement, using ARP (automatic pattern recognition), which has been crucial for structure based drug design (SBDD). Diffraction data is fed directly into the computer program and a protein crystallization model produced automatically. Various programs have been developed to assess docking of virtual ligands into known target receptor sites and scoring of their suitability and fit, determined by energy. Some algorithms seem to have some bias towards certain chemical families; this can be reduced by using multiple docking algorithms simultaneously (Charifson et al. 1999). Software programmers and chemical modellers must remember to take into account the natural properties of protein molecules, as they are more flexible and accommodating of small changes than the rigidity suggested by traditional computer programs, although some programs now attempt to recreate this (Schapira et al 2000). Optimal results for structure based drug design are likely to be achieved by combining virtual and experimental methods, such as ‘SAR-NMR’ technology advocated by Shuker, Fesik and colleagues (1996). Microarrays DNA microarrays have been constructed following the sequencing of the human genome, using cDNA to study thousands of genes. From this has stemmed the growth of proteomics and protein biochips, as these are the functional molecules encoded by the genome. Protein arrays/biochips consist of immobilized proteins, which can be used, in the drug development context, to study ligand-receptor interactions (Lueking et al. 2005). Interactions of known pharmaceutical chemicals with proteins can also be explored. For example, Leflunomide (an isoxazole derivative) has been shown to have anti-inflammatory properties in vivo. Analysis of protein interactions using an array revealed that it was not only interacting with the suspected mitochondrial enzyme, but a number of other proteins in the cell, such as pyruvate kinase (Mangold et al. 1999). As the majority of drug targets are proteins, and many of the drugs themselves proteins too, protein arrays are likely to become more popular, as well as hig her throughput. CONCLUSION CHOOSING THE BEST HTS ASSAY: The literature reveals numerous modifications and validated systems of all the possible assays that are suitable for adaptation to high throughput screening in drug discovery. Many of the traditional weak points of each assay have therefore been addressed in this way, making critici

Procrastination Essay -- essays research papers

Procrastination Procrastination is the avoidance of doing a task that needs to be accomplished. Procrastination has a high potential for painful consequences. It may interfere with our personal or academic success. There are those of us who wait until the due date is a day away. I am not talking about making sure the money is in the bank. I am talking about putting it off because it is a tedious chore that we do not enjoy doing. Procrastination is a big problem for many, and one that can harm your career. Whether your procrastination causes you to arrive late at work or late for meetings, or keeps you from turning projects in on time, employers do not look positively upon it There are several reasons why we procrastinate. If a project is absolutely overwhelming, to the point where you don't even start it, break it down into small, specific steps. Do one or two each day. If you complete a step and are motivated to continue, fine. But if you're not, that's fine too because you have only committed to one small piece. Just don't stop before completing that piece. If there is no immediate payoff because the project is long term, build in mini-completion points. Design a reward system similar to what you do with a task you don't like. Creating instant gratification will motivate you until you reach the final destination. If you know you can handle the project but just don't know where to start, start anywhere. Just do something. Write a title on a piece of paper. Then write something else. Eventually you'll be led to where you need to go. But it takes a little bit of momentum to get the ball rolling. This doesn't mean that you'll use any of the material y ou start with. This is fine - you need a good finished product, not a good first draft. A final, common reason for procrastination is perfectionism. Be aware that there is a difference between doing something right and doing the right thing. Perfectionists can spend their time on the wrong thing, i.e. hanging and re-hanging a picture on the office wall. Looks great, but is it getting you anywhere? If the task is meaningless in the long run, it doesn't really matter if you do it perfectly. You can still do it well, just don't let it consume you. If perfectionism is keeping you from beginning a task, reevaluate whether the ... ...ntil the last minute to start a difficult task can also be used as a defense for poor performance. You can always claim that it would have been better if there was more time. (The report would have been more comprehensive if you had been given more time to do it.) It can shield you from the consequences that you expect to occur after the project is completed. For example, not accepting a high visibility special assignment will shield you from the consequences of a) being in the limelight and possibly failing or b) doing well and being offered more challenge. This could take the form of a new position as the office manager, a relocation or a new set of circumstances that may be frightening. If you are not feeling up to the rigorous standards that you have set for success, or are trying to live up to others have set that the expectations for your performance, delay can be used as a means of self-protection. When you find yourself blocked, unable to start a task and you have tried everything else, ask yourself: "Is there anything, no matter how small, that I am willing to do?" When you find that small thing, you are no longer procrastinating.