Nucleic Acids Are The Organic Compounds

Nucleic Acids Are The Organic Compounds Nucleic acids were discovered by Friedrich Miescher, a Swiss biochemist, in 1869. He called them nucleic because he believed that they occurred only in the nucleus of the cell [1]. Nucleic Acids are the organic compounds found in the chromosomes of living cells and in viruses. The structure of the nucleic acids in a cell determines the structure of the proteins produced in that cell. Since proteins are the building blocks of life, nucleic acids can be considered the blueprints of life. But chemically we can define nucleic acids as molecules that are comprised of monomers known as nucleotides.[2,3] The two main types of nucleic acids are:- Deoxyribonucleic acid ( DNA) :-It ordinarily occurs only in the cell nucleus. Ribonucleic acid ( RNA):-It is found both in the nucleus and in the cytoplasm (the main part of the cell exclusive of the nucleus). Both DNA and RNA combine with protein materials to carry out cell division and cell repair processes. [4] Deoxyribonucleic acid ( DNA) A type of nucleic acid that constitutes the molecular basis of heredity. It is found principally in the nucleus of all cells where it forms part of the chromosome, or in the cytoplasm of cells lacking a nucleus, such as bacteria. It acts as the carrier of genetic information containing the instructions (code) to make proteins. It consists of two single chains of nucleotides, which are twisted round each other to form a double helix or spiral. The nucleotides contain sugar (deoxyribose), phosphate and the bases (adenine, cytosine, guanine and thymine). The two strands of DNA are held together by hydrogen bonds located between specific pairs of bases (adenine to thymine and cytosine to guanine). The sequence of bases and consequently gene sequence is sometimes altered, causing mutation. DNA includes the sugar deoxyribose, which has one less oxygen atom than ribose the sugar found in RNA, hence the name is deoxy-ribose nucleic acid.[6,7] Each DNA molecule is a long two-stranded chain. The strands are made up of subunits called nucleotides, each containing a sugar (deoxyribose), a phosphate group, and one of four nitrogenous bases, adenine, guanine, thymine, and cytosine, denoted A, G, T, and C, respectively. A given strand contains nucleotides bearing each of these four. The information carried by a given gene is coded in the sequence in which the nucleotides bearing different bases a soccur along the strand. The chemical and physical properties of DNA suit it for both replication and transfer of information . Fig 1.A 3D rendered computer model of the DNA double helix. [16] Structure Of DNA Its structure, with two strands wound around each other in a double helix to resemble a twisted ladder, was first described (1953) by Francis Crick and James D. Watson and they named it as Watson and Crick model of DNA which states that: Fig 2. Double helix structure of DNA[ It is a double helix with two right handed helical polydeoxy ribonucleotide strands twisted around the same central axis. The two strands are anti parallel. The phosphodiester linkages of one of these strands run in 5 to 3 direction while the other strand runs in 3 to 5 direction. The bases are stacked inside the helix in planes perpendicular to the helical axis. These two strands are held together by hydrogen bonds. In addition to hydrogen bonds, other forces e.g., hydrophobic interactions between stacked bases are also responsible for stability and maintenance of double helix. Adenine always pairs with thymine while guanine always pairs with cytosine. A-T pair has 2 hydrogen bonds while G-C pair has 3 hydrogen bonds. Hence, G C is more stronger than A=T. The content of adenine is equal to the content of thymine and the content of guanine is equal to the content of cytosine. This is Chargaffs rule, which is proved by the complementary base pairing in DNA structure. The genetic information is present only on one strand known as template strand. The double helix structure contains major and minor grooves in which proteins interact with DNA. The diameter of double helix is 2nm. The double helical structure repeats at intervals of 3.4 nm (one completer turn) which corresponds to 10 base pairs.[7,8,9] Different forms of DNA Double helical structure exists in six different forms. They are A-DNA, B-DNA, C-DNA, D-DNA, E-DNA and Z-DNA. Among these only 3 forms of DNA are important. They are B-DNA, A-DNA and Z-DNA. 5.1 B-DNA:-This is nothing but the double helical structure described by Watson and Crick. It has 10 base pairs in each turn. 5.2 A-DNA:-This is also a right handed helix. It has 11 base pairs per turn. 5.3 Z-DNA:-This is a left handed helix. It has 12 base pairs per turn. The strands in this form move in a zig-zag manner and hence it is called as Z-DNA.[12,13] Properties of DNA The properties shown by DNA that allows for transmission of genetic information to new cells are as follows:- Replication Transcription Translation 6.1 Replication An important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell. Fig3. Replication Process in DNA [30] 6.2 Transcription Transcription is the process in which DNA nucleic acids transfer the cells genetic information into RNA materials. In essence, each DNA strand manufactures a corresponding RNA strand. Three types of RNA are manufactured within this process. [13]Messenger RNAs (mRNA) are designed to carry the genetic information received from the DNA strands. Ribosomal RNAs (rRNA) reside in the cells cytoplasm, and are responsible for decoding, or translating the genetic instructions into cell processes. Transfer RNAs (tRNA) are responsible for gathering whatever amino acids are needed for protein synthesis.[14] Fig4. Transcription In DNA [20] 6.3 Translation Translation is the process in which RNA molecules create the proteins needed to sustain necessary cell functions. This is accomplished by converting the genetic code contained in the messenger RNAs into amino acid strings, which is what make protein molecules. This conversion process takes place within the ribosomes, which are located in the cells cytoplasm. [14] Functions of DNA (deoxyribonucleic acid): DNA is a permanent storage place for genetic information. DNA controls the synthesis of RNA (ribonucleic acid). The sequence of nitrogenous bases in DNA determines the protein development in new cells. The function of the double helix formation of DNA is to ensure that no disorders occur. This is because the second identical strand of DNA that runs anti-parallel to the first is a backup in case of lost or destroyed genetic information. Ex. Downs Syndrome or Sickle Cell Anemia.[16,17] RNA( ribonucleic acid) It is another type of nucleic acid which functions in cellular protein synthesis in all living cells. They play an essential role in the synthesis of proteins. On hydrolysis they yield the pentose sugar ribose, the purine bases adenine and guanine, the pyrimidine bases cytosine and uracil, and phosphoric acid.RNA occurs mostly in the cytoplasm in the eukaryotic cells. A small amount occurs in the nucleus of the cell, as a constituent of nucleolus. RNA is a single polynucleotide chain composed of nucleotides of adenine, guanine, cytosine and uracil. Thymine nucleotides are absent. Structure of RNA RiboNucleic Acids consist of: Ribose (a pentose = sugar with 5 carbons) Phosphoric Acid Organic (nitrogenous) bases: Purines (Adenine and Guanine) and Pyrimidines (Cytosine and Uracil) An RNA molecule is a linear polymer in which the monomers (nucleotides) are linked together by means of phosphodiester bridges, or bonds. These bonds link the 3 carbon in the ribose of one nucleotide to the 5 carbon in the ribose of the adjacent nucleotide. Fig 5. Chemical Structure of RNA [19] Purines: Adenine A Guanine G Pyrimidines: Uracil U Cytosine C Fig 6. Organic Bases Structure of RNA [21] Structural Difference between RNA and DNA RNA differs, however, from DNA because it does not form an analogous double helical structure. The pyrimidine base thymine is modified in that it lacks a methyl group and the resulting uracil takes its place in base pairing. Together, the presence of uracil in place of thymine, and the 2-OH in the ribose constitute the two chemical differences between RNA and DNA which is shown in Fig 7. Fig7. Structural difference between RNA and DNA [19] Types Of RNA 11.1 Messenger RNA (mRNA) It represents about 5 to 10% of the total RNA. It is synthesised from DNA as and when necessary. It carries the genetic information in the form of a specific sequence of nitrogen bases arranged in triplet codons, which are copies from the code in DNA. 11.2 Transfer RNA (tRNA) It represents about 10 to 15% of the total RNA in the cell. It has the shortest molecule having only about 80 to 100 nucleotides. The polynucleotide chain is folded on itself to have the shape of a cloverleaf. The molecule has three lateral loops, a DHU loop, a t loop and an anticodon loop. The anticodon loop bears a triplet combination of nitrogen bases, called anticodon. It is complementary to a codon of mRNA. The tRNA molecule is meant for recognising and carrying particular types of amino acids to the sites of protein synthesis. 11.3 Ribosomal RNA (rRNA) It represents nearly 80% of the total RNA in the cell. It always occurs bound to basic proteins in ribosomes. It takes part in assembling the amino acids brought by tRNA, into a polypeptide chain, based on the sequence of codons in mRNA. [19,20] Functions of RNA RNA serves the following functions: mRNA has a significant role in genetic code. tRNA is responsible for transferring amino acids to the site of protein synthesis (ribosomes). rRNA assembles the amino acids into a polypeptide chain. It also serves as a primer for replication of DNA. RNA serves as the genetic material in some plant viruses. [21] Applications of Nucleic Acid Nucleic acids find a number of exciting applications in various fields. . 13.1 Microarrays and biosensors PNA(peptide nucleic acid) can be used on microarrays and other biosensors. PNA microarray combined with PCR could detect genetically modified organisms (GMOs) in food 13.2 Imaging probes and FISH PNA is especially good for FISH because it can bind to DNA or RNA quickly even under low salt or other unfavorable conditions for DNA.PNA s specificity was utilized to discriminate 16S rRNA of bacteria species in drinking water. PNA probes also have been used for in vivo imaging of mRNA for cancer research. [23] 13.3 Catalysts and receptors Nucleic acids can also be employed as enzymes (for catalysis) and receptors (for ligand binding). Increasingly, researchers are making interesting use of these molecules, now collectively called functional nucleic acids. 13.4 Body functions Essential bodily functions such as growth, repair and reproduction all rely on nucleic acid for direction and support. Nucleic acid is in nearly every cell of the body. [24] 13.5 Medicinal Uses Gen-Probe Inc. (San Diego, California) introduced nucleic acid probe-based diagnostic products for gonorrhea and chlamydia. It is a direct test based on DNA ribosomal RNA hybridization, with demonstrated sensitivity of 89.9% to 97.1%, and specificity of 93% to 98%. [23, 26] FUTURE PROSPECTS OF NUCLEIC ACID Nucleic-acid-amplification test (NAAT) is used for the diagnosis of TB(tuberculosis) by the new method instead of conventional smear/culture method. So NAAT will simply take us to a new era of advanced, effective, and rapid TB diagnosis. Attempts are done to employ nucleic acids in effective gene therapy which is believe to become commonplace in recent years. At the same time, however, the study of nucleic acids has revealed remarkable properties of DNA and RNA molecules that could make them attractive therapeutic agents, independent of their well-known ability to encode biologically active proteins. In future we will find alternative uses of nucleic acids that do not rely on virus-based vectors or even on gene transfer. Tuberculosis (TB) is an important target for clinical testing due to the increase in incidence of the disease in this decade. Both Roche and Gen-Probe,great are developing kits for rapid TB testing. The Roche kit is based on PCR technology, while Gen-Probes kit uses transcription mediated amplification. [27, 28, 29]

Odysseus,the Hero, Homer :: essays research papers

Odysseus, The Hero   Ã‚  Ã‚  Ã‚  Ã‚  In today*s eclectic society, everybody*s heroes are different. However, during the era Homer*s The Odyssey was created all heroes had same characteristics. Heroes were the people who saved people, they were courageous wise and had fighting spirit. Odysseus, the main character in Homer*s epic poem was clever brave and a great strategist.Ê Although he has these strengths, he has some negative qualities, but most of his heroic qualities still hold true today.   Ã‚  Ã‚  Ã‚  Ã‚  Odysseus possesses heroic qualities, such as bravery, wisdom, a strategic thinking and honorable. Most of the story in The Odyssey is told by Odysseus, so we can say from his narration that he is eloquent. Book 9 shows Odysseus* positive and?@negative qualities.Ê When he escapes from Cyclops* cave he showed that he was brave and a great strategist.Ê When he poked Cyclops* eye with pike of olive, he decided not to kill him because if he killed Cyclops, he would not be able to get out of the cave.Ê This also shows he was wise and able to think about the situation before doing anything.Ê Another example that shows that he is brave that he went to the Hades, which was a feared by many.Ê By his eloquence and cleverness Odysseus could get Nausicaa to assist him, and his devotion to his wife makes him so honorable.Ê He showed sensitivity when he met his mother and when he heard the song of the Trojan War.   Ã‚  Ã‚  Ã‚  Ã‚  However, Odysseus* qualities are not considered heroic today are his impulsiveness, arrogance, and curiosity.Ê He struggle?@with these points. Odysseus went to Cyclops* cave because he was curious but didn*t think what may happen next. When Odysseus was able to escape from Cyclops* cave, he yelled to Cyclops identifying himself because of his pride. That made Cyclops so angry that he prayed to his father Poseidon to destroy Odysseus. The result of that is Odysseus* companions all died before Odysseus could return home. If he didn*t reveal his name to Cyclops, maybe his companions wouldn*t died. Even though he has negative characteristics it shows Odysseus is just a human. He is not a god or a perfect man. His negative points aren*t favorable, but they make his positive points look stronger. If he were a god or a perfect man, his positive points wouldn*t be special or great. When his weak points get him into trouble, his strong points rescue him. For example, his impulsiveness with Cyclops almost destroyed him and his companions but his bravery and clever strategy

“the Catcher in the Rye Expository Essay”

â€Å"The catcher in the rye expository essay† The catcher in the rye is a book I have read and really enjoyed because of the plot and the characters in the novel. â€Å"I always call it the catcher of the rye of the new generation. † (www. Thinkexist. comJessica sharzer) the novel takes place in New York. This narrativeis really enjoyable and fun to read. This novel deals with a lot of issues and this is the reason I enjoyed this innovative story. The story takes place in New York City and this is one of the many reasons why I like this novel. The story was also written in a narrative format because of the way the main character: Holden Coldenfield. Holden narrates throughout the entire narrative because he is the narrator. He has been kicked out of eight different schools due to the way he acts in class and towards his peers. He also smokes to keep his stress down because of the way he acts. Every single person who knows of Holden would not like or even care for him. The only person who cared for him is his little sister. The family does not know he was kicked out of his new school Yancy academy. Holden cares for his little sister Phoebe Caulfield. Holden also stays at a hotel for a couple of nights after being kicked of his poised school Yancy academy. He tries to act like an adult to show he is not afraid even though he is sixteen. When Holden couldn’t afford to stay at the hotel anymore he decided to stay with a teacher who tries to molest him while he sleeps and Holden then decides to leave the teachers house without calling the police. While he is walking he happens upon a bar and decides to walk in even though he is sixteen but he has a fake driver’s license and he sees a girl dancing by herself and so he decides to ask her out and it does not end well for him. Holden decides to leave New York for another city because he knows that his family will send him to another prep school. His family might start to miss him since he was their only son and they took him for granted. Before leaving he finds his sister while she is on a field trip in central park and takes her to a merry go round before leaving. Since Holden really cares for Phoebe he explains to her that he is leaving and won’t be coming back and he tells her that he loves her. He also tells Phoebe the dream he had explaining him being a catcher in the rye and how he was catching little kids as they ran off a cliff. After he is done telling her this she asks him if she could go with him when he leaves New York. Finally, the catcher in the rye is a novel that I have read and enjoyed because of the characters and the plot in the novel. â€Å"I will always call it the catcher in the rye of the new generation. †(Jessica sharzer)

What Is a Sampling Distribution

Statistical sampling is used quite often in statistics. In this process, we aim to determine something about a population. Since populations are typically large in size, we form a statistical sample by selecting a subset of the population that is of a predetermined size. By studying the sample we can use inferential statistics to determine something about the population. A statistical sample of size n involves a single group of n individuals or subjects that have been randomly chosen from the population. Closely related to the concept of a statistical sample is a sampling distribution. Origin of Sampling Distributions A sampling distribution occurs when we form more than one simple random sample of the same size from a given population. These samples are considered to be independent of one another. So if an individual is in one sample, then it has the same likelihood of being in the next sample that is taken. We calculate a particular statistic for each sample. This could be a sample mean, a sample variance or a sample proportion. Since a statistic depends upon the sample that we have, each sample will typically produce a different value for the statistic of interest. The range of the values that have been produced is what gives us our sampling distribution. Sampling Distribution for Means For an example, we will consider the sampling distribution for the mean. The mean of a population is a parameter that is typically unknown. If we select a sample of size 100, then the mean of this sample is easily computed by adding all values together and then dividing by the total number of data points, in this case, 100. One sample of size 100 may give us a mean of 50. Another such sample may have a mean of 49. Another 51 and another sample could have mean of 50.5. The distribution of these sample means gives us a sampling distribution. We would want to consider more than just four sample means as we have done above. With several more sample means we would have a good idea of the shape of the sampling distribution. Why Do We Care? Sampling Distributions may seem fairly abstract and theoretical. However, there are some very important consequences from using these. One of the main advantages is that we eliminate the variability that is present in statistics. For instance, suppose we start with a population with a mean of ÃŽ ¼ and standard deviation of ÏÆ'. The standard deviation gives us a measurement of how spread out the distribution is. We will compare this to a sampling distribution obtained by forming simple random samples of size n. The sampling distribution of the mean will still have a mean of ÃŽ ¼, but the standard deviation is different. The standard deviation for a sampling distribution becomes ÏÆ'/√ n. Thus we have the following A sample size of 4 allows us to have a sampling distribution with a standard deviation of ÏÆ'/2.A sample size of 9 allows us to have a sampling distribution with a standard deviation of ÏÆ'/3.A sample size of 25 allows us to have a sampling distribution with a standard deviation of ÏÆ'/5.A sample size of 100 allows us to have a sampling distribution with a standard deviation of ÏÆ'/10. In Practice In the practice of statistics, we rarely form sampling distributions. Instead, we treat statistics derived from a simple random sample of size n as if they are one point along a corresponding sampling distribution. This emphasizes again why we desire to have relatively large sample sizes. The larger the sample size, the less variation that we will obtain in our statistic. Note that, other than the center and spread, we are unable to say anything about the shape of our sampling distribution. It turns out that under some fairly broad conditions, the Central Limit Theorem can be applied to tell us something quite amazing about the shape of a sampling distribution.