Mutation of DNA Essay Example | Topics and Well Written Essays - 1250 words

Mutation of DNA - Essay Example Transversion mutation involves the substitution of purine by pyrimidine and pyrimidine by purine. This type of mutation is rare due to steric problems of pairing purines with purines, and pyrimidine with pyrimidines. This type of mutation takes place due to chemical modification in a base. The chemical modification is caused due to two reactions one is deamination and second is depurination. In deamination Cytosine occasionally loose an amino group and then it is converted to Uracil. This resulted in pairing of Uracil-Guanin instead of Cytosine-Guanin. It is well known that Uracil pairs with Adenin. After Uracil-Adenin pair in first round of replication, thymine takes the place of Uracil in second round of replication. And finally Cytosine - Guanin pair is converted to Adenin - thymine Pair. In depurination loss of purine group (Adenine or Guanin) takes place. Due to deletion and insertion of one or a few nucleotides in DNA molecule, the shifting of reading frame of nucleotide takes place either in backward or in forward position, this results into a mutation. This is known as frameshift mutation. Generally this mutation occurs where there is a short repeated nucleotide sequence. Any agent that directly cause damage to the DNA alters the base sequence or interferes with repairing system is known as mutagens. Mutagens may be some chemical or radiation. Here we are discussing how the mutagen can act: 1) Base Analogues: A base analogue is a chemical compound similar to the one or four bases of DNA. During normal replication process this base analogue can be incorporated into growing polynucleotide chain. For Example 5-Bromouracil (5-BU) is an analogue of thymine. It can pair with adenine in polynucleotide chain by replacing thymine. During the replication keto-form of 5-BU Substitutes for thymine and the replication of an initial Adenin:Thymine (A:T) pair becomes an A:BU pair. The rare enol form of 5-BU that pairs with Guanin is the first mutagenic round of replication. In the next round of replication Guanin pairs with cytosine. So that transition is completed from A:T to G:C pair. 2) Chemical Changing the Specificity of Hydrogen Bonding. There are many chemicals that after incorporation in DNA change the specificity of hydrogen bonding. For example Nitrous Oxide (HNO2) converts the amino group of the bases into keto group through oxidative deamination. Deamination of adenine results in formation of hypoxanthine, the pairing behavior of which is like guanine. Hence it pairs with cytosin

Accounting and taxation Essay Example | Topics and Well Written Essays - 1000 words

Accounting and taxation - Essay Example The employment status of an employee has been categorized as employed or self-employed.This categorization is based upon the terms and conditions of the relevant association.It is important to mention that such classification is important as separate rules have been promulgated which are applicable to specific conditions of employment in special circumstances. It is important for an employee to realise that he/she should be aware of her job description along with lists of the designated authorities to whom he/she is responsible. It is significant to evaluate the capacity of your designation, which shall be verified against the standard classification of employed or self-employed, "it is important to know whether you are working for that person in an employed capacity or in a self-employed capacity as an independent contractor". This classification is significant in terms of imposition of tax bracket, the employment status is crucial to determine "the charge to tax on income from that employment or self-employment, and determines the class of NICs, which are to be paid" (Helen, 2000).The differentiation between the self-employed and employed is possible after evaluation of "contract of service or under a contract for services". It is important with reference to tax and NIC that "there is no statutory definition of a contract of service or of a contract for services", it is indeed the relationship towards the institution which is significant in assessment. The application of common law principles is critical for the determination of the nature of a contact. The courts have developed specific factors and assessment, the affirmative response towards series of factors helps in the classification of employed personnel. The questions includes, "do they have to do the work themselves; can someone tell them at any time what to do, where to carry out the work or when and how to do it; can they work a set amount of hours; can someone move them from task to task; are they paid by the hour, week, or month; can they get overtime pay or bonus payment". The affirmative response towards following suggest the strong possibility of self-employed personnel, "can they hire someone to do the work or engage helpers at their own expense; do they risk their own money; do they provide the main items of equipment they need to do their job, not just the small tools that many employees provide for themselves; do they agree to do a job for a fixed price regardless of how long the job may take; can they decide what work to do, how and when to do the work and where to provide the services; do they regularly work for a number of different people; do they have to correct unsatisfactory work in their own time and at their own expense" (Helen, 2000). As per legal regulations, contract has been regarded as oral and/or implied agreement between minimum two parties. The common elements of valid contract service and contract for services include, "the intention to enter into le gal relations; an offer (usually of work) and its acceptance (an agreement); consideration (for example, in return for performing work the worker receives payment)". The establishment of contact is essential, it is also important to settle the terms and conditions of the contract against "case law laid down by the courts over the years" (Greg, 2006). Issues The legal requirement envisaged by the courts include "basic approach to identify the factors present; weigh those that point to self-employment against those that point the other way; and then stand back and consider the picture that emerges" (Helen, 2000). The contract shall include the discussed features, which shall essentially reflect the nature of employment and will assist in differentiation of employment status. The understanding and interpretation of relationship between the parties is not of significant interest, "it is the reality of the relationship that matters, the intention of the parties has to be taken into account and can be decisive where the relationship is ambiguous