Bacteriophage Lambda Lysogenic Cycle Biology Essay
Bacteriophage Lambda Lysogenic Cycle Biology Essay. Viruses are tiny agents that cause infections in a wide range of hosts including animals, plants, bacteria and other viruses. In particular, viruses that infect bacteria are called bacteriophages, bacterio meaning “bacteria” in Greek and phage meaning “to eat”. Bacteriophages are able to undergo lytic and lysogenic cycle to replicate; however, most undergo one or the other cycle to replicate. An example of a bacteriophage that is able to undergo both cycles is bacteriophage lambda (phage lambda). Bacteriophage lambda infects only the bacterium Escherichia coli strain k-12. Phage lambda is unique in its ability to turn replication genes on or off depending on the host’s condition. When E. coli is infected with phage lambda and the cell dies due to an environmental factor, the phage will switch from the lysogenic to the lytic replication cycle. Bacteriophage lambda was discovered by Esther Lederberg in 1950 while she was working in a laboratory with E. coli strain k-12. Lederberg is considered a pioneer of bacterial genetics; she was also an immunologist and microbiologist. She flourished academically, receiving a doctorate from the University of Wisconsin where she worked with many other pioneers of microbiology, genetics and immunology, including: Andre Lwoff, Edward Lawrie Tatum, George Wells Beadle, Frances Crick and James Watson. While at the University of Wisconsin, Lederberg was using ultraviolet light on E. coli strain k-12 to mutagenize that specific strain of the bacteria. After prolonged exposure to the ultraviolet light, the bacteria stopped growing and its condition slowly began to deteriorate. An hour and a half after the exposure to the ultraviolet light ceased, the bacteria began to lyse (burst). This led Lederberg to the discovery of bacteriophage lambda. The E. coli sample that Lederberg was using was infected with bacteriophage lambda. The phage was not detected because it was in the lysogenic cycle, which meant that the phage was a prophage, and thus that the phage genome was integrated within the bacterial genome. Bacteriophage lambda sensed that the bacteria was about to die, so it switched its replication genes on and converted to lytic replication, therefore causing the cell to lyse and release the phage into the environment. Lederberg is also accredited with the discovery of induction; the process of when the lysogenic cycle is terminated and the lytic cycle is activated due to adverse conditions caused by ultraviolet light. Lederberg, along with her team of researchers, was awarded the Pasteur award in 1956. Viruses have many different anatomical structures depending on what kind of cells they infect. The anatomical feature that is similar throughout all bacteriophage is the capsid. The capsid or head is a shell made out of protein that contains DNA or RNA, depending on the virus. The capsid also contains some internal proteins. The capsid can have many different configurations, from a polygon-shaped sphere, like an icosahedral, or a rod-shaped helix. The main functions of the capsid are that it allows the virion to attach to its host via special sites on the surface, contains the internal proteins that allows the virus to penetrate the host cell membrane, which enables it to inject the infectious DNA or RNA into the host cell’s cytoplasm, and that it provides protection for the nucleic acid from the environment and digestion by enzymes. The capsid has structural subunits called capsomers that may contain one or many polypeptide chains. Some viruses have a secondary structure that protects the capsid itself, this is called an envelope. Not all viruses have an envelope; the envelope is made up of glyco-proteins and surrounds the entire capsid for optimum protection. The envelope has two lipid layers intermingled with protein molecules, a lipoprotein bi-layer, and also has a mixture of material that consist of the viral origin and some material from the membrane of the host cell. Besides a capsid, some viruses also contain a tail that is attached to the capsid which helps the virus penetrate the host cell’s outer membrane and allows the virus to inject the DNA or RNA into the host cell. The tail consists of two main structures: the tail fibers and a tail sheath. The tail fibers are tiny leg like formations that help the phage attach on to the bacterial cell by clinging on to the surface receptors. The tail sheath is a tube like structure that runs from the capsid to the tail fibers; the tail sheath digs into the cell membrane of the host and the DNA or RNA travels down the sheath and into the cytoplasm of the host and the infectious cycle begins. For viruses without tails, specialized spikes are protruding directly from the capsid that play a similar role to that of tails; the spikes are made up of proteins and help the virus invade the host cell. Bacteriophage lambda has a capsid with an icosahedral configuration that is 55 nanometers in diameter that contains 350-575 capsomers or subunits of 37,000 Daltons; the capsomers are positioned in groups of 5 and 6 subunits or pentamers and hexamers. The tail is 180 micrometers long and contains a single tail fiber that is 25 nanometers long. Bacteriophage lambda does not possess an enveloped capsid. Although viruses are not considered living organisms, they do have genetic material that allows them to replicate with the aid of a host. Viruses can have a genome that is made up of either DNA or RNA and the nucleic acid can be single stranded or double stranded. Viruses can either have DNA as their nucleic acid or RNA, they cannot contain both. DNA viruses are commonly double stranded, but they can be single stranded, have a lower rate of mutation, are more stable and the DNA replication takes place in the nucleus of the host. In contrast, RNA viruses are usually single stranded, although some are double stranded, are very susceptible to mutation, and are less stable and the RNA replication takes place in the cytoplasm of the host cell instead of the nucleus. RNA viruses can come in two different varieties, they can either be positive sensed or negative sensed. Positive-sensed RNA viruses are infectious without any need for transcription; negative sensed RNA viruses are not infectious until they undergo transcription which will turn them into infectious positive sensed RNA viruses. The following are examples of viruses with double stranded DNA genome: adenoviruses, herpes simplex viruses, varicella-zoster viruses and bacteriophages T2, T4 and lambda. Bacteriophage Ï†X174 and adeno-associated viruses (AAV) are examples of single stranded DNA viruses. Some positive sensed RNA viruses are: polioviruses, rhinoviruses, corona viruses and tobacco mosaic virus. Negative sensed RNA viruses include: human metapneumovirus, parainfluenza viruses and respiratory syncytial viruses. Viruses also have a great deal of variability when is comes to the number of base pairs a genome contains. A virus can have as little as a couple thousand base pairs to over a million base pairs, as found in Acanthamoeba polyphaga mimivirus. Bacteriophage lambda has a linear, single stranded DNA composition that is housed within the icosahedral capsid. The genome of the phage contains 48,490 base pairs that make up the two strands of the cos site. The mode of infection of bacteriophage lambda is very similar to other viruses but there are some differences as to which receptor the phage attaches to the host cell. The journey of the phages genome, from the phage itself to the genes being integrated within the host cells’ chromosome, can be characterized in the following steps: The tail fiber of bacteriophage lambda attaches to the E. coli receptor that is specifically meant for the sugar, maltose. E. coli has a gene product, called lam B, which is a maltose operon protein molecule. A protein, J protein, on bacteriophage lambda’s tail fiber is able to intermingle with the lam B gene of the host which enables the phage to safely attach on to the host cell membrane. Since the phage attaches to a maltose receptor, the host does not see the phage as a threat but believes that the phage is just another sugar entering the membrane. After the phage has attached to the host, the phage genome is injected into the outer membrane of E. coli; the phage genome then travels within sugar transport pathway, which that allow it to enter the inner membrane of the host cell. Once the phage genome has entered the cytoplasm of the host cell, the phage genome converts from a linear configuration to a circular configuration by connecting the sticky ends of its genome, which are guanine and cytosine rich. The circular configuration protects the phage genome from being degraded or destroyed by nuclease enzymes from the host cell. After the circular chromosome of the phage reaches the nucleus, the genome is unwound using helicase, where negative super-coils are integrated and the phage chromosome begins to unravel. The host gyrase relieves any strain that is caused by the unraveling of the phage chromosome. The unwound, linear phage chromosome is integrated within the host genome and phage replication begins. After the phage genetic material has been injected into the cell, the viral genome travels to the nucleus to be replicated via lytic or lysogenic cycles. In they lysogenic cycle, bacteriophage lambda genome is integrated into the host cell’s genome by an attachment site called attÎ». . AttP is a gene sequence that is found on the phage genome. And the sequence on the host is attB. Using Holliday junction, the two sequences are swapped with the help of host cell’s IHF protein and the phage Int protein. The two proteins form an intasome when they bind to attP; intasome is a recombination of the two genomes. The phage has now successfully incorporated its genome into the host’s genome, allowing the phage genetic material to be replicated along with they host’s genome, without the host realizing that it has been infected. The integrated phage is now referred to as a prophage; prophage is now in a mutual relationship with the host, the phage is being replicated without spending any of its only energy and the host is not immune to another infection from a similar bacteriophage. The phage will continue to replicate until induction causes it to convert to the lytic cycle. In the lytic cycle, the phage genome replaces the host genome, so only the phage genome is being replicated. Replication of genes in the lytic cycle is accomplished in two stages. In the first stage or early gene replication, transcription and translation of the phage DNA occurs and key enzymes, like helicase, primase and polymerase, are replicated. In the second stage or late replication, genes for the capsid and tail are replicated. After gene replication has been completed, taking about 60 minutes to complete, the early genes are taken up by the new capsid and the host cell beings to burst and release the progeny. Most viruses will either enter the lysogenic cycle and then the lytic cycle or they will enter the lytic cycle directly. What makes bacteriophage lambda so unique is its ability to decide whether the lytic cycle or lysogenic cycle is more energy efficient depending on the host’s condition. If the host is nutritionally sound and has high protease activity, the phage will opt to select the lytic cycle, as it requires more energy from the host and yields progeny faster. On the other hand, if the host has lowered protease activity as well as depleted nutrition, the phage will go into the lysogenic cycle and replicate until the host is no longer able to support the phage. Bacteriophage lambda is detected in a similar manner as other phages, and that is by the formation of plagues on a lawn of bacterial growth. The plagues will only form on a lawn of E. coli strain k-12, as that is the only strain that bacteriophage lambda is able to infect. Because of its ability to select which replication cycle will yield the most progeny, they phage makes an excellent cloning vector, this ability allows the phage to be grown in a test tube. Another reason that lambda phage makes a good cloning vector is that it has a large DNA sequence, which allows larger foreign DNA to be inserted into the phage genome. Bacteriophage lambda was discovered unintentional by Esther Lederberg. The phage has a single tail fiber and has an icosahedral capsid. It infects E. coli strain k-12 by binding on to its maltose receptor. Once the phage has entered the nucleus of the host, it will determine whether the lytic or lysogenic replication cycle should be used depending on the nutrition value of the host. This ability makes bacteriophage lambda very dissimilar to other phages and it also makes the phage a superior model as a cloning vector. Bacteriophage Lambda Lysogenic Cycle Biology Essay
Strayer University Week 4 Social Forces and Issues Shaping Curriculum Planning Paper
best assignment help Strayer University Week 4 Social Forces and Issues Shaping Curriculum Planning Paper.
I’m working on a writing case study and need an explanation to help me study.
Using your answers to the discussion questions throughout this course and the information you researched from the Week 4 assignment Social Forces and Issues Shaping Curriculum Planning, you will create a proposal to update the curriculum you used. Remember to relate your answers to the student population, neighborhood demographics, alignment to state and national standards, and other issues that affect the curriculum. InstructionsWrite a 6–8 page paper where you address the following points: Identify the immediate issues with the curriculum.Address the following:Test scores.Age of the current curriculum. Need to implement technology.Social forces.Revision of state or national standards. Discuss who will be on your curriculum team.How will you ensure that you have a diverse team? Explain the role of key positions and who you expect to fill those positions. Describe how you will conduct a needs assessment. Use a variety of resources and methods, not just test results. Explore at least three current trends that include technology integration in the classroom and current methodology in your grade or subject area.These issues can be ideas such as:Flipped classroom.Online instruction.Differentiated learning.The latest teaching methods. Expanded use of technology for students such as iPads for everyone. Discuss practical considerations with these issues such as cost, teacher training, logistics, et cetera.This course requires the use of Strayer Writing Standards. For assistance and information, please refer to the Strayer Writing Standards link in the left-hand menu of your course. Check with your professor for any additional instructions.The specific course learning outcome associated with this assignment is:Create a proposal for curriculum planning that addresses the immediate issues.UnacceptableBelow 70% FFair70-79% CProficient80-89% BExemplary90-100% A1. Identify immediate issues with the curriculum.Points Range:0 (0.00%) – 41.4 (13.80%)Did not submit or incompletely identified immediate issues with the curriculum.Points Range:42 (14.00%) – 47.4 (15.80%)Partially identified immediate issues with the curriculum.Points Range:48 (16.00%) – 53.4 (17.80%)Satisfactorily identified immediate issues with the curriculum.Points Range:54 (18.00%) – 60 (20.00%)Thoroughly identified immediate issues with the curriculum.2. Discuss who will be on the curriculum team.Points Range:0 (0.00%) – 41.4 (13.80%)Did not submit or incompletely discussed who will be on the curriculum team.Points Range:42 (14.00%) – 47.4 (15.80%)Partially discussed who will be on the curriculum team.Points Range:48 (16.00%) – 53.4 (17.80%)Satisfactorily discussed who will be on the curriculum team.Points Range:54 (18.00%) – 60 (20.00%)Thoroughly discussed who will be on the curriculum team.3. Describe how to conduct a needs assessment.Points Range:0 (0.00%) – 41.4 (13.80%)Did not submit or incompletely described how to conduct a needs assessment.Points Range:42 (14.00%) – 47.4 (15.80%)Partially described how to conduct a needs assessment.Points Range:48 (16.00%) – 53.4 (17.80%)Satisfactorily described how to conduct a needs assessment.Points Range:54 (18.00%) – 60 (20.00%)Thoroughly described how to conduct a needs assessment.4. Explore 3 current trends.Points Range:0 (0.00%) – 41.4 (13.80%)Did not submit or incompletely explored 3 current trends.Points Range:42 (14.00%) – 47.4 (15.80%)Partially explored 3 current trends.Points Range:48 (16.00%) – 53.4 (17.80%)Satisfactorily explored 3 current trends.Points Range:54 (18.00%) – 60 (20.00%)Thoroughly explored 3 current trends.5. Clarity and writing mechanics.Points Range:0 (0.00%) – 20.7 (6.90%)More than 6 errors presentPoints Range:21 (7.00%) – 23.7 (7.90%)5-6 errors presentPoints Range:24 (8.00%) – 26.7 (8.90%)3-4 errors presentPoints Range:27 (9.00%) – 30 (10.00%)Thoroughly described the three key issues for each social force. 0-2 errors present6. Use references to support your claims, including quotes, facts, and illustrations from the articles in the text and three (3) other outside scholarly sources published in the last two years.Points Range:0 (0.00%) – 20.7 (6.90%)No references provided.Points Range:21 (7.00%) – 23.7 (7.90%)Does not meet the required number of references; some or all references poor quality choices.Points Range:24 (8.00%) – 26.7 (8.90%)Meets number of required references; all references high quality choices.Points Range:27 (9.00%) – 30 (10.00%)Exceeds number of required references; all references high quality choices.Name:Rubric for Assignment 2: Curriculum Planning: A FoundationDescription:EDU564 Assignment 2: Curriculum Planning: A Foundation
Strayer University Week 4 Social Forces and Issues Shaping Curriculum Planning Paper
Impact of Boeing 707, the Bell X-1 and the NASA Mercury Capsule on Modern Aviation Essay
Table of Contents Introduction Boeing 707 The Bell X-1 The NASA Mercury Capsule Conclusions Works Cited Introduction Just like any other industry or field, space travel and exploration has overtime undergone a revolution with major names making the revolution history of this particular history. Such names like Boeing 707, the Bell X-1 and the NASA Mercury capsule remain in history as the triggers of the revolution and as a result, these innovations are of great importance in the study of the Aviation history. As regarding these names, it is conventional knowledge in the history of aviation that these names are in the heart of the historical transformation of the industry. This paper focuses on these historical names with the view of identifying and explaining the role played by each of these players in the revolution and development of the aircrafts present today. Boeing 707 This was an innovation by Boeing between 1958 and 1979. The major characteristic feature that identifies this innovation was a narrow size, and its swept-wing design. The capacity of this plane ranged from 120 to 140 people and could cruise range of between 3,680 and 3,735 nautical miles (Bradley 36). Though it was not the first of its kind, this jet obtained its fame from the fact that it was the first one to achieve commercial success. In the development of the Boeing 707, the design of the wing was a major concern. This pushed for the study of the wing design of preceding models including the B-47 and C-97. One thing that the designers agreed is that no matter the outcome, the result of the designed must serve both military and civil purposes (Bradley 46). This realization finally realized the adoption of the 367-80, commonly referred to as “dash 80”. This was powered by turbojet engine, more precisely the Pratt
Infidelity as a Cause of Divorce and Stress Disorder Research Paper
Infidelity as a Cause of Divorce and Stress Disorder Research Paper. Introduction Nowadays, it is not an easy task to create a good marriage and keep it for a long period of time. Men, as well as women, get an access to a number of temptations. Sometimes, people are just not able to resist the possibilities they have and become the main begetters of their own mistakes and frustrations. Among the existing variety of mistakes and wrong decisions, infidelity is the main cause of a family disruption, divorce, and stress disorders. Infidelity is a serious issue for consideration due to the myths existing around and the inabilities to comprehend how to cope with the cases of infidelity and overcome possible stress disorders. Divorces, as well as stress disorders, may be caused by different reasons, still, the idea of infidelity is rather provocative as people themselves have a right to choose whether to cheat and break the vow like “till death do us part” or not; and the current paper discusses the aspects of infidelity, its myths, reasons, and outcomes, analyzes the impact of infidelity on the development of stress disorders, and explains how people can avoid infidelity and save their families. Definitions of Infidelity One of the strangest things about infidelity is that people may understand its essence in many different ways because of their own attitudes infidelity or because of the myths people create from time to time to try to justify their actions. For example, the Oxford Dictionaries (2015) explain infidelity as an action of being unfaithful to a spouse. In fact, this explanation seems to be too general as it provides a person with a chance to interpret the idea of faith in a family differently. Many researchers and philosophers have made the attempt to introduce their own identification of infidelity and offer their explanations. Brown (2013) indicates that infidelity is the act in which more than 55% of men and about 45% of women are involved. Stosny (2013) introduces infidelity as the act that presupposes lies, manipulations, stealing, or cheating separately or together and leads to divorce. In fact, the act of infidelity is everything that contradicts the principles of a successful marriage. Two people make a decision to spend the rest of their lives together, create their own vows, and swear to support each other under different circumstances. However, there are not many people, who can truly predict their future and be sure of the loyalty of the chosen spouse. This is why, unfortunately, the cases of infidelity are usual and understandable. Anyway, infidelity should be defined as an act of betrayal, either emotional or sexual, by one or both spouses that can or cannot be forgiven. People, who make a decision to break the vows given at the beginning of their marriages, should realize that their infidelities usually touch upon several people (parents, fellows, and even the lives and families of those, whom they betray with). Myths about Infidelity An affair that causes the act of infidelity can happen to anyone. Nowadays, people are eager to defend their rights and promote the abilities to choose what they want and when they want. It is hard to prove their incorrectness unless some legal perspectives are considered. Nowadays, the law is the only thing that can stop people from making mistakes or take responsibility for something already done. However, the law usually has nothing in common with infidelity unless some points are discussed in a special prenuptial agreement. Why is it so difficult to survive infidelity and just not to cheat staying a loyal to the chosen spouse? Many people think that infidelity leads to divorce because those, who begin affairs, usually look for someone younger and more attractive. The current examples of the celebrities (Jude Law, Arnold Schwarzenegger, or Woody Allan) prove that marriage infidelity may be not based on beauty or age. People can break their promises because of different reasons. Sometimes, they do not even need the reasons. People also believe that infidelity happens because something goes wrong with their marriages and a person, who cheats once, can cheat again. All these facts are false indeed. Everything depends on people and their abilities, and the nature of each person is unique indeed. Some people cannot even realize why they actually cheat and let infidelity in their family. There are also many men and women, who like to cheat because they can do it or because someone else is doing it. These myths about infidelity help to realize why it is so difficult to understand how infidelity may become the first reason for divorce. Infidelity in a Marriage as the First Cause of Divorce Infidelity may be of two types: sexual and emotional. The former takes place when one of the spouses begins sexual affairs with another person. The latter may have nothing in common with a real cheat; the spouse may betray talking to another person with something too personal, refusing doing something with another spouse, or being unable to understand what happens around (SubotnikInfidelity as a Cause of Divorce and Stress Disorder Research Paper