DNA Structure Chains - Free Essay Example

Sample details Pages: 6 Words: 1829 Downloads: 10 Date added: 2017/06/26 Category Biology Essay Type Research paper Tags: DNA Essay Did you like this example? 1. Introduction 1.1 DNA Structure DNA is a polymer made of subunits called as nucleotides. Each nucleotide consists of a deoxiribose sugar, a phosphste, and a nitrogenous base (Genetics from Genes to Genomes). Don’t waste time! Our writers will create an original "DNA Structure Chains" essay for you Create order Watson and Crick proposed the structure for DNA (shown schematically in Figure 1 a). This is the presence of two polynucleotide strands coiling around a common axis and those strands linked together by a specific hydrogen bond scheme between the purine and pyrimidine bases (Figure 1 b), viz. adenine (A) with thymine (T) and guanine (G) with cytosine (C). The carbon atoms of the deoxyribose sugar are distinguished from atoms of the deoxyribose within the nucleotide base by the use of primed numbers from 1-5. The phosphodieser bonds always form a covalent link between the 3 carbon of one nucleoside and the 5 carbon of the following nucleoside. The consistent orientation of the nucleotide building blocks gives a chain overall direction, such that the two ends of a single chain are chemically distinct. At the 5 end, the sugar of the terminal nucleotide has a free 5 carbon atom and at the other 3 end of the chain, it is the 3 carbon of the final nucleotide that is free (Genetics from Genes to Genomes). In the model, two DNA chains spiral around an axis with the sugar-phosphate backbones on the outside and pairs of bases (one from each chain) meeting in the middle. Although both chains wind around the helix axis in a right-handed sense, chemically one of them runs 5 to 3 upward, while the other runs in the opposite direction of 5 to 3 downward. In short, the two chains are antiparallel. The base pairs are essentially flat and perpendicular to the helix axis, and the planes of the sugars are roughly perpendicular to the base pairs. As the two chains spiral about the helix axis, they wrap around each other spiral about the helix axis, they wrap around each other once every 10 base pairs, or once every 34ÃÆ'†¦ (Genes to genomes). In a space-filling representation of the model, the overall shape is that of a cylinder with a diameter of 20ÃÆ'†¦ whose axis is the axis of the double helix. The backbones spiral around the axis like threads on a screw, but because there are two backbones, there are two threads, and these two threads are vertically displaced from each other. This displacement of the backbones generates two grooves, one much wider than the other, that also spiral around the helix axis. Biochemists refer to the wider groove as the major groove and the narrower one as the minor groove. The two chains of double helix are held together by hydrogen bonds between complementary base pairs, A-T and G-C. Since the overall shapes of the two base pairs are quite similar, either pair can fit into the structure at each position along with DNA. Moreover, each base pair can be accommodated in the structure in two ways that are the reverse of each other: an A purine may be on strand 1 with its corresponding T pyrimidine on strand 2 or the T pyrimidine may be on strand 1 and the A purine on strand 2. In addition A-C and G-T pairs do not fit well together; that is, they do not easily form hydrogen bonds. The DNA molec ule is essentially a polynucleotide or a polymer chain formed by phosphate diester groups joining b-D-deoxyribose sugars through their 3 and 5 hydroxyl groups (Figure 3). The backbone of the DNA molecule thus consists of six single bonds about which rotations can take place (also indicated in Figure 3) giving rise to various possible conformations/structures for the polymeric chain. As mentioned above, the canonical Watson-Crick DNA model is a two-stranded helical structure, in which the two chains are held together by hydrogen bonds between the purine (A,G) and pyrimidine (T,C) bases. There are 10 nucleotides per turn, separated by + 36 rotation and 3.4 ÃÆ'†¦ translation along the helix axis,in each of the two chains and the two chains are aligned in mutually anti-parallel orientations (Figures 1 a and 4) (Manju Bensal) DNA can inter-convert between two well-defined forms, viz. A and B (Figure 2). The molecular structures corresponding to these two forms were later show n to be essentially similar in their handedness, chain orientation and hydrogen bonding scheme. Subsequently it has become clear that the DNA molecule has an enormous ability to undergo structural changes depending on its environment by twisting, turning and stretching, leading to a pantheon of DNA structures6. Several of these structural polymorphs of DNA have now been experimentally characterized using X-ray diffraction, NMR or other spectroscopic studies and are found to vary considerably from the Watson-Crick type structure (Manju Bensal). 1.2 Principle of Agarose Gel Electrophoresis Electrophoresis is defined as movement of small ions and charged molecules in solution under the influence of an electric field (Gel Electrophoresis of Nucleic Acid, A Practical Approach). Agarose gel electrophoresis is a widely used method that separates molecules based upon charge, size and shape. It is particularly useful in separating charged biomolecules such as DNA, RNA and proteins (Lab Electrophoresis). Agarose gel electrophoresis possesses great resolving power, yet is relatively simple and straightforward to perform. The gel is made by dissolving agarose powder in boiling buffer solution. The solution is then cooled to approximately 55oC and poured into a mol containing a comb that makes well when solution is polymerised (Lab Electrophoresis). Electrophoresis is carried out in the gels cast either in tubes or as slabs. A number of gel materials have been used successfully, including agar, agarose, and polyacrylamide. Agar and agarose gels are made by heating the gra nular material in the appropriate electrolyte buffer, casting the gels and allowing them to set on cooling. The resolving power of these gels depends on the concentration of dissolved agar or agarose; dilute gels are used for very large DNA molecules and more concentrated gels for low molecular weight DNA (Gel Electrophoresis of Nuclecic Acid, A Practical Approach). Samples are prepared for electrophoresis by mixing them with components that will give the mixture density, such as glycerol or sucrose. This makes the samples denser than the electrophoresis buffer. These samples can then be loaded with a micropipette or transfer pipet into wells that were created in the gel by a template during casting. The dense samples sink through the buffer and remain in the wells (Lab Electrophoresis). A direct current power supply is connected to the electrophoresis apparatus and current is applied. Charge molecules in the sample enter the gel through the walls of the wells. Molecules ha ving a net negative charge migrate towards the positive electrode (anode) while net positively charged molecules migrate towards the negative electrode (cathode). Within a range, the higher the applied voltage, the faster the samples migrate. The buffer serves as a conductor of electricity and to control pH. The pH is important to the charge and stability of biological molecules (Lab Electrophoresis). The rate of migration depends on the size and shape of the molecule, the charge carried. In an electric field at moderate pH, negatively-charged DNA molecules migrate towards the anode. A fractionation is achieved because large molecules move more slowly through the gel than small molecules and selection of DNA within a given size range is obtained by selecting a gel of appropriate pore size. Electrolytes used in electrophoresis generally consist of an aqueous buffer, containing a chelating agent such as ethylenediaminetetractate (EDTA) and a nuclease inhibitor such as sodium dodecyl sulphate (SDS). A number of factors affect the fractionation of RNA. Increasing the current leads to higher rates of migration, but the flow of current also results in the production of heat, which, if excessive, adversely affects the separation by causing trailing and broadening of the zones. 1.3 Fluorescence 1.3.1 Silver Staining Ethidium bromide staining is the conventional laboratory technique for the detection of DNA. Switzer et al (1979) originally introduced silver staining technique for the detection and analysis of proteins. Currently, silver staining is sometimes used to detect DNA fragments, including short interspersed nuclear elements, VNTR detection, and SNPs in various experiments (Yan-Chung Han et al, 2008). The new method is much efficient and sensitive for polymorphism DNA analysis and the detection of small amount of nucleic acid (Sommerville and Wang, 1981; Boulikas and Hancock, 1981; Goldman and Merril, 1982; and Guillemette and Lewis, 1983) but more versatile silver staining is needed for analysis of complex DNA profiles generated in DNA amplification fingerprinting and DNA sequencing (Anolles and Gresshoff, 1994). The ethidium bromide staining of DNA is time-consuming as they require a lot of preparation and handling of several solutions prior to use and needs expensive and bulky fluorescence imaging equipment. Furthermore, the sensitivity, color uniformity, and storage time of the staining gels are not ideal (Yan-Chuang Han et al, 2008). Moreover, Ethidium bromide used for staining of DNA as a conventional method is a carcinogenic substance and a cost of waster disposal. Many modifications to silver staining method have been reported since the introduction of silver staining method for the analysis of proteins and nucleic acid analysis in agarose and polyacrylamide gels. It has been reported that some procedures used to stain nucleic acids in polyacrylamide gels are not suitable for agarose gels due to differences in the chemical compositions of both matrices. The agarose matrix has the disadvantage of nonspecific depositions of silver ions resulting in high background (Willoughby and Lambert 1983, Peats 1983, and Lasne et al 1983). Those protocols developed in order to reduce the nonspecific stain in agarose gels involve time-consuming pretreatment s teps with K2Cr2O7 or Na2S2O3 (Zalazar et al, 2001). During image development almost all staining procedures reduce silver ion to colloidal silver, which is then deposited in the immediate vicinity of the staining substratum. For optimal image contrast, the level of silver reduction in the gel matrix must be kept to a minimum level. This is performed by appropriate modulation of the speed of the reduction process, which depends mainly on the pH, the absolute and relative concentrations of silver and reducing agents, and the rate constant of the reaction (Anolles and Gresshoff, 1994). Silver staining is also useful for the microarray technology in order to impede the interference of fluorescent label with the hybridisation process. This advantage is achieved by application of silver staining after the hybridization process. Silver staining also eliminates the need of fluorescence imaging equipment in microarray technology by means of using a film scanner. The aims of the pres ent study are to optimize a silver staining protocol performed for a commercially obtained DNA molecular weight marker, in which the procedure is modified. The detection limit of silver staining is investigated and is compared with ethidium bromide staining. Moreover, some of the siver staining methods are varied and are compared with ethidium bromide staining. The silver staining protocol is modified inorder to increase the sensitivity and reduce background staining. After a suitable protocol is optimized DNA are deposited on filter paper at various dilutions and stained with the optimized. This has implications for the development of portable biosensors with label free detection.

Beowulf, By Seamus Heaney - 930 Words

Beowulf is an epic poem written 1000 to 1300 years ago in Old English and translated by Seamus Heaney into Modern English. Beowulf is a significant piece of literature art work not only because it is one of the earliest known works, but also because it reflects and represents the authors, the Anglo-Saxons’ culture and values. At first, this story was passed around orally, from one person to another. Then, later on, the Anglo-Saxons wrote the entire story down into a manuscript. As well as the Anglo-Saxons loved their stories, they loved to boast, too. Boasting wasn’t an arrogant thing to do in their society, instead, it was socially acceptable, or even essential in one’s life. The Anglo-Saxons loved telling stories and boasting; they also liked material things such as gold swords and silver shields. Those were the rewards a soldier receives from their king, which represents their qualities and achievements. Beowulf reveals the Anglo-Saxons’ values in ma ny parts of the poem. Stories appeared the most frequently in Beowulf. The first 64 lines of Beowulf is a story about the old king Shield Sheafson, â€Å"So. The Spear-Danes in days gone by / and the kings who ruled them had courage and greatness. / We have heard of those princes’ heroic campaigns. †(1-3), this already proves the importance of stories to the Anglo-Saxons. Stories were mostly what the Anglo-Saxons did for entertainment. People would gather around in a hall, with food and their drinks, and they would begin toShow MoreRelatedBeowulf, By Seamus Heaney1971 Words   |  8 Pagesform in many unique ways perceived by society. People hold many opinions on what a true hero is. However, our society is gifted with a clear representation on what qualities make a true hero in the epic poem Beowulf translated by Seamus Heaney. Although there is no true author, fortunately Seamus Heaney’s translation gives a deeper analysis which allows the reader to better grip key concepts and ge t the closest possible to the actual translation. This epic poem dates back to around 700 to 1000 AD duringRead MoreThe Epic Of Beowulf By Seamus Heaney2116 Words   |  9 PagesBiography: Beowulf is an old story, that was composed somewhere between the middle of the seventh and tenth century, that used to be told orally in front of large groups of people, never being written down until much later when the original teller was long dead. Therefore the original author of Beowulf is unknown, however Seamus Heaney is one of the many to have translated it from old english into current english so many others can enjoy it as well. Seamus Heaney was born on April 13 in 1939. BornRead MoreReview Of Beowulf By Seamus Heaney2154 Words   |  9 PagesSydney Pritchard Mr. McMullan 10th Grade Honors English 13 July 2015 Book Report Title: Beowulf Author: Seamus Heaney Date of Publication: 2000 Historical Context: Genre: epic heroic poem Plot: During the Dark Ages of Europe, in the late 5th century, powerful Scandinavian empires emerged. One of those, the Danish empire, prospered under its ruler, Hrothgar, a decendent of the great Shield Sheafson. To commemorate his warriors for helping him build his empire, Hrothgar built a great mead hall, a placeRead MoreBeowulf a Poem Translated by Seamus Heaney Essay1072 Words   |  5 PagesIn the poem, Beowulf, by an unknown poet, as translated by Seamus Heaney, we see many monstrous behaviors. A few of the examples stand out more than the rest: wanton destruction, a woman acting as a man, and the act of killing one’s kin. Wanton destruction goes against the ideals that governed the Anglo-Saxon culture. The warrior kings had duties to uphold. We see that they revered kings who would bring protection and give freely to the young and old and not cause harm. One good illustration ofRead MoreBeowulf And The Anglo Saxon Period1740 Words   |  7 PagesBeowulf The original poem, Beowulf, goes back to the Anglo-Saxon period in c. 650 and c.1100. Authors translated Beowulf many times in the Anglo-Saxon period to present day. It displays how a hero should be in the real world. He helps the people in the village and slays monsters. Everyone in the village looks up to him as he acts as if he were a role model. Beowulf, the protagonist in the translated Beowulf by Seamus Heaney, is a hero of his village, stands for bravery, strong will, and noblenessRead MoreValue Of Loyalty In Beowulf949 Words   |  4 PagesIn this thrilling poem Beowulf by Seamus Heaney, Beowulf shows characteristics of a noble warrior who takes on different journeys against monsters to be crowned as the undisputed warrior and bring home prestige for his fellow clan members. Beowulf first task on his path to gain glory is to defeat the merciless monster Grendel, who haunts Heorot for twelve long winters. If he wins this battle, he does not only gain glory and respect for himself, but also for his king and clan. He exhibits all theRead MoreTheme Of Loyalty In Beowulf813 Words   |  4 Pagesthemes that emerge throughout the poem ‘Beowulf by Seamus Heaney’. With a focus on an extract in Beowulf, this essay will explore how Seamus Heaney shows the themes loyalty and courage through the use of diction and imagery. In this extract, Beowulf is seen battling the dragon with his companions, however, Beowulf’s companions all leave except for Wiglaf. Wiglaf expresses his loyalty and dedication towards Beowulf through a speech and bravely helps Beowulf. Beowulf then uses his sword to try and killRead MoreTheme Of Heroism In Beowulf1544 Words   |  7 PagesBeowulf demonstrates the qualities and traits of being an ideal hero. In the poem it explores Beowulf ‘s heroism in two distinct stages which are youth and age. Beowulf has three separate and very difficult conflicts that involve Grendel, Grendel’s mother and the dragon. When you are viewing these major encounters with the three different people Beowulf demonstrates the importance of heroic code. There is a much clearer division between Beowulf’s adolescent heroism as a warrior as well as in onesRead MoreCultural Progression through Beowulf Essay examples569 Words   |  3 PagesBeowulf is an Old English poem. It was wr itten sometime between 700 and 1,000 A.D. Over the years it has been edited and rewritten countless times. Some of the more recent versions do their best to stay as close to the original story as possible while others make rather large changes to make it more engaging for today’s audiences Seamus Heaney translated a version of Beowulf in 2001. He tried hard to translate the story in a way that best represents the original. Heaney’s version is bilingual withRead MoreLanguage in Beowulf Essay767 Words   |  4 Pagesancient but timeles epic poem Beowulf. Beowulf was written in Old English by an unknown author between the centuries of 800 AD and 1000 AD. Year after year, a new translation is made by an author. Each translation is completely different, yet still the same poem. It is tedious for authors to make their translation literal to the original epic, while simultaneously making it understandable, modern, and readable. Many have tried to accomplish this, but personally I find that Seamus Heaney’s translation of

Gang Violence among Adolescents Free Essays

Whenever I see young adolescents loitering or hanging out in streets, doing nothing worthwhile but trying to act tough while showing it to their friends or hurting other people, I feel nothing but regret. They should have been at school, learning things that could help them have a better job and future, or at home helping their family and having fun with them. They could do so much if only they make better use of their time and youth. We will write a custom essay sample on Gang Violence among Adolescents or any similar topic only for you Order Now Local governments are faced with the problems associated with gang violence among adolescents. Preventing adolescents from wasting their lives should be a matter of importance for communities, and this should be prioritized because adolescents can have a better future away from the streets. When crowds of young people gather, they may take a group identity. Other groups or even them, may identify themselves as gangs. Furthermore, cliques tend to identify the formation of a gang as a result of threats or conflicts, police pressure and media coverage. According to studies, gang behavior is â€Å"situational in nature,† and the attribution of hostile behavior to one gang may further contribute to the formation and identity of a gang. In addition, it may be further solidified once â€Å"neighbors, police, school authorities, and others identify unsupervised groups of young people as gangs† (Short, 1996, p. 3). Preventing young people from being associated with violent gangs have been one of the priorities of communities. Past studies showed that gang violence continue to plague communities as gang-related crimes increased over time. For instance, in 1995, it showed that gang-related homicides increased. From 1979 to 1994 alone, a record of 7,288 gang-related homicides was documented in Los Angeles Police Department (LAPD). The proportion of gang-related homicides increased from 18 to 43 percent (Maceo, 1995). These figures alone would tell how worse gang violence has become. Gang violence brings young people to jails. In fact, many adolescents have been charged for being involved in criminal activities. Just this year, a 15-year-old student was killed by a young man who was an alleged member of a violent street gang. The 18-year-old suspect, who pleaded guilty, was charged with 30 years in prison (Castaneda, 2009). This scenario should not be the kind of life that young people must have. Families should be the first ones involved as they are the primary influencing factors in the lives of adolescents. In the case mentioned above, the parents of the victim were completely unaware that their son was a member of a gang. They learned about it when it was too late to save their son. Parents should know the things that their children are being involved in, and must find ways to talk to their children about the consequences of joining gangs that tend to be violent. Parents should encourage their children to be involved in more worthwhile activities, such as sports, that would further develop their skills and improve their talents and make them better individuals. The community also has responsibilities in preventing the existence of violent gangs. There should be constant patrols especially in dark and derelict areas. It would be also beneficial if there are programs designed to lure young people away from the streets, such as volunteer works or business ventures that would teach adolescents the importance of working and being properly compensated for a good work done. Moreover, a center for young people can help those who are trying to get out of gangs and trying to change. Attention must be focused to those who want a way out because they might be harmed due to their willingness to have a better life. These young people should really have a good, fruitful life that a violent gang can never give them. How to cite Gang Violence among Adolescents, Papers