Viruses can only reproduce by infecting living cells. There are two main types of viral infections: lytic infections immediately use the host cell to replicate new viruses which then burst out and kill the cell, while lysogenic infections insert viral DNA into the host cell's genome where it remains inactive for many generations before replicating in a lytic cycle. Viruses either replicate immediately through lytic infection or initially persist in an inactive state through lysogenic infection within the host cell before replicating.
General Characters and Classification of Viruses. Includes ICTV classification and Baltimore classification of viruses. A brief explanation of the Viral structure and Lifecycle.
Bacteriophage is the most common and extensively studied virus. The life cycle of bacteriophages. The transfer of their genetic system via the process of transduction (Generalised and Specialised) and studying the gene mapping in phages. This theoretical explanation about viruses and their genetic system will help the learner in the fields of biotechnology, microbiology, basic science, life science, and various other fields of biology.
A comprehensive illustration about viruses and their genetic system. The life cycle of bacteriophages. The transfer of their genetic system via the process of transduction (Generalised and Specialised) and studying the gene mapping in phages.
Instructions for Submissions thorugh G- Classroom.pptxJheel Barad
This presentation provides a briefing on how to upload submissions and documents in Google Classroom. It was prepared as part of an orientation for new Sainik School in-service teacher trainees. As a training officer, my goal is to ensure that you are comfortable and proficient with this essential tool for managing assignments and fostering student engagement.
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An EFL lesson about the current events in Palestine. It is intended to be for intermediate students who wish to increase their listening skills through a short lesson in power point.
Model Attribute Check Company Auto PropertyCeline George
In Odoo, the multi-company feature allows you to manage multiple companies within a single Odoo database instance. Each company can have its own configurations while still sharing common resources such as products, customers, and suppliers.
Honest Reviews of Tim Han LMA Course Program.pptxtimhan337
Personal development courses are widely available today, with each one promising life-changing outcomes. Tim Han’s Life Mastery Achievers (LMA) Course has drawn a lot of interest. In addition to offering my frank assessment of Success Insider’s LMA Course, this piece examines the course’s effects via a variety of Tim Han LMA course reviews and Success Insider comments.
Operation “Blue Star” is the only event in the history of Independent India where the state went into war with its own people. Even after about 40 years it is not clear if it was culmination of states anger over people of the region, a political game of power or start of dictatorial chapter in the democratic setup.
The people of Punjab felt alienated from main stream due to denial of their just demands during a long democratic struggle since independence. As it happen all over the word, it led to militant struggle with great loss of lives of military, police and civilian personnel. Killing of Indira Gandhi and massacre of innocent Sikhs in Delhi and other India cities was also associated with this movement.
The Roman Empire A Historical Colossus.pdfkaushalkr1407
The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
Under Augustus, the empire experienced the Pax Romana, a 200-year period of relative peace and stability. Augustus reformed the military, established efficient administrative systems, and initiated grand construction projects. The empire's borders expanded, encompassing territories from Britain to Egypt and from Spain to the Euphrates. Roman legions, renowned for their discipline and engineering prowess, secured and maintained these vast territories, building roads, fortifications, and cities that facilitated control and integration.
The Roman Empire’s society was hierarchical, with a rigid class system. At the top were the patricians, wealthy elites who held significant political power. Below them were the plebeians, free citizens with limited political influence, and the vast numbers of slaves who formed the backbone of the economy. The family unit was central, governed by the paterfamilias, the male head who held absolute authority.
Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
3. The Discovery of Viruses
1892
Dmitri Ivanovski
1892
Dmitri Ivanovski
1897
Martinus Beijerinck
1897
Martinus Beijerinck
1935
Wendell Stanley
1935
Wendell Stanley
6. Viral Infections
Viruses use their genetic information to reproduce inside living cells.
Lysogenic
infection
Lysogenic
infection
Lytic
infection
Lytic
infection
7. Lytic Infections
The virus injects DNA into
a bacterium.
The virus injects DNA into
a bacterium.
Viral genes are transcribed
by the host cell.
Viral genes are transcribed
by the host cell.
The bacterium
makes new viral
proteins and nucleic
acid.
The bacterium
makes new viral
proteins and nucleic
acid.
The proteins and
nucleic acids assemble
into new viruses.
The proteins and
nucleic acids assemble
into new viruses.
Viral enzymes lyse the
bacterium’s cell wall.
The new viruses
escape.
Viral enzymes lyse the
bacterium’s cell wall.
The new viruses
escape.
8. Lytic Infections Analogy
A lytic virus is similar to the Wild West of the American frontier.
The host cell’s
DNA is chopped up.
Virus uses host cell
to make viral DNA
and viral proteins.
The host cell bursts,
releasing hundreds
of virus particles.
9. Lysogenic Infections
The viral DNA inserts
itself into the bacterial
chromosome.
The viral DNA inserts
itself into the bacterial
chromosome.
Prophage
The prophage may replicate
with the bacterium for many
generations.
The prophage may replicate
with the bacterium for many
generations.
The prophage can exit the
bacterial chromosome and
enter a lytic cycle.
The prophage can exit the
bacterial chromosome and
enter a lytic cycle.
The virus injects DNA
into the bacterium.
The virus injects DNA
into the bacterium.
10. An RNA Virus: The Common Cold
Once the cold virus has penetrated the host’s cells, it uses the
host’s cellular machinery to replicate itself.
Cytoplasm
The virus makes many
copies of its RNA.
The copies are
translated by the host
into new viral parts.
The parts assemble
into new viruses and
burst from the host cell.
11. An RNA Virus: HIV
HIV makes a DNA copy of itself that inserts into the host’s DNA.
There, it may remain inactive for many cell cycles.
Cytoplasm
A DNA copy of the
viral RNA is made.
The copy is
inserted into the
host’s genome.
It is later transcribed
and translated into new
viral parts.
The parts assemble into
new viruses and burst from
the host cell.
DNA
13. Summary of Viruses
• Viruses reproduce by infecting living cells.
• Some viruses replicate immediately;
others initially persist in an inactive state
within the host.
Lysogenic infection
Lytic infection
Editor's Notes
Read the lesson title aloud to students.
Click to show each of the learning objectives.
Ask students if they have ever missed out on some important event, such as a football game, because they had a cold.
Explain that a cold is an example of an illness caused by a virus.
Tell students: This lesson describes the structure of viruses and explains what happens when a virus infects a cell.
Distribute the worksheet for this lesson to students and tell them to use it to record the similarities and differences between viruses and cells as they are discussed in the lesson.
Make sure that students understand that at the end of the presentation, they should be able to explain how viruses reproduce and what happens after a virus infects a cell.
Discuss the events that led to the discovery of viruses.
Click to reveal the first scientist involved in the discovery.
Tell students: In 1892, Dmitri Ivanovski demonstrated that the cause of tobacco mosaic disease was found in the liquid extracted from infected plants.
Click to reveal the next scientist involved in the discovery.
Tell students: In 1897, Martinus Beijerinck suggested that tiny particles in the juice caused the disease; he named these particles viruses, after the Latin word for “poison.”
Click to reveal the next scientist involved in the discovery.
Tell students: In 1935, Wendell Stanley isolated crystals of tobacco mosaic virus.
Explain that American biochemist Wendell Stanley is the scientist who isolated crystals of tobacco mosaic virus. He knew that living organisms do not crystallize, so he inferred that viruses were not truly alive.
This is still recognized as a valid conclusion today.
Tell students: A virus is a nonliving particle made of proteins, nucleic acids, and sometimes lipids.
Ask: How do viruses reproduce?
Answer: Viruses can reproduce only by infecting living cells.
Click to reveal the answer.
Explain to students that viruses can differ widely in size and structure. The simplest viruses contain only a few genes. The most complex may have hundreds of genes.
Click to focus on the T4 bacteriophage.
Point out the head, the tail sheath, and the tail fiber.
Ask: What is the magnification necessary to see a T4 bacteriophage with a transmission electron microscope (TEM)?
Answer: 60,000x
Click to focus on the tobacco mosaic virus.
Point out that this virus looks similar to the tail sheath of the T4 bacteriophage, but that it does not have the head and the tail fiber of the bacteriophage. Also, emphasize the difference in size.
Ask: What is the magnification necessary to see a tobacco mosaic virus with a transmission electron microscope?
Answer: 400,000x
Make sure that students are aware of the order of magnitude difference between this and the T4 bacteriophage.
Click to focus on the influenza virus.
Point out to students that this virus looks nothing like the other two.
Review the parts shown and labeled and tell students to notice the magnification necessary for this virus to be visible is only 21,000x.
Ask: What kind of nucleic acid does each virus type have?
Answer: The T4 bacteriophage has DNA; the tobacco mosaic virus and influenza virus have RNA.
Ask: What happens after a virus infects a cell?
Answer: Inside living cells, viruses use their genetic information to reproduce.
Click to reveal this answer.
Explain that some viruses replicate immediately. This is called a lytic infection.
Click to reveal the lytic infection label.
Other viruses initially persist in an inactive state within the host. This is called a lysogenic infection.
Click to reveal the lysogenic infection label.
Tell students: A virus enters a bacterial cell, makes copies of itself, and causes the cell to burst, or lyse.
Step students through the typical process of a lytic infection.
Click to highlight the first step.
Tell students: The DNA core inside a protein capsid binds to the surface of a host cell. The virus injects its DNA into the cell, and the cell then begins to make messenger RNA (mRNA) from the viral genes.
Click to highlight the second step.
Tell students: The viral mRNA is translated into viral proteins that act like a molecular wrecking crew, chopping up the cell’s DNA.
Click to highlight the third step.
Tell students: Under the control of viral genes, the host cell now makes thousands of copies of viral nucleic acid and capsid proteins, enabling the virus to reproduce.
Click to highlight the fourth step.
Tell students: The viral DNA is assembled into new virus particles.
Click to highlight the final step.
Tell students: Before long, the infected cell lyses, releasing hundreds of virus particles that may go on to infect other cells.
Ask: In a lytic infection, how does the virus make copies of itself?
Answer: by inserting its genetic information into a cell, which directs the cell to make and assemble new viral parts
Ask: Why can a lytic virus remain in a particular host cell only for a limited time?
Answer: It eventually destroys the host cell by causing it to burst.
Use the analogy of a lytic virus being like an outlaw in the Wild West. The virus makes certain demands on the host.
Tell students: First, the outlaw eliminates the town’s existing authority.
Click to reveal the first step.
Explain that this is like the host cell’s DNA being chopped up.
Tell students: Next, the outlaw demands to be outfitted with new equipment from the local townspeople.
Click to reveal the second step.
Explain that this is like the virus using the host cell to make viral DNA and viral proteins.
Tell students: Finally, the outlaw forms a gang and leaves the town to attack new communities.
Click to highlight the third step.
Explain that this is like when the host cell bursts and releases hundreds of virus particles.
To make sure that students grasp both the analogy and the way in which a lytic virus works, ask the following questions.
Ask: In this analogy, what represents the host cell?
Answer: the town
Ask: Think about how viruses enter host cells. Extend the analogy to describe the outlaw’s entrance into town.
Answer: Answers should describe the outlaw being sneaky or using trickery to gain entrance to the town.
Ask: Think about how viruses exit host cells. Extend the analogy to describe the condition of the town after the outlaw leaves.
Answer: Answers will vary, but should describe the outlaw destroying the town or leaving it in disarray as he leaves.
Step students through the typical process of a lysogenic infection.
Click to highlight the first step.
Tell students: Viral nucleic acid is inserted into the host cell’s DNA, where it is replicated along with the host DNA without damaging the host.
Explain to students that the virus’ DNA becomes embedded in the host’s DNA and is called a prophage.
Click to highlight this step and to point out the prophage.
Tell students: The prophage may remain part of the DNA of the host cell for many generations. It is replicated along with the host DNA without damaging the host. Viral DNA multiplies as the host cells reproduce. In this way, each generation of daughter cells derived from the original host cell is infected.
Click to highlight this step.
Explain that influences from the environment—including radiation, heat, and certain chemicals—trigger the prophage to become active. It then removes itself from the host cell DNA and reproduces by forming new virus particles. The lysogenic infection, at this point, becomes an active lytic infection.
Click to highlight this step.
Work with students to extend the analogy of the outlaw in the Wild West to a lysogenic infection.
Ask: How would you modify the story of the outlaw in the Wild West to make it analogous to a lysogenic cycle?
Answer: A correct response will include an analogy for the prophage being a part of the bacterium for an extended period of time.
Sample answer: The outlaw pretends to be looking for work, takes a job at a nearby ranch, and hides out there for a time.
Tell students: About 70 percent of viruses contain RNA rather than DNA. In humans, RNA viruses cause a wide range of infections, from relatively mild colds to influenza and AIDS. Certain kinds of cancer also begin with an infection by viral RNA.
Ask: What happens when you get a cold?
Answer: Cold viruses attack with a very simple, fast-acting infection.
Explain to students that a capsid settles on a cell, typically in the host’s nose, and is brought inside, where a viral protein makes many new copies of the viral RNA.
Click to reveal this step.
Tell students: The host cell’s ribosomes mistake the viral RNA for the host’s own mRNA and translate it into capsids and other viral proteins.
Click to reveal this step.
Explain that the new capsids assemble around the viral RNA copies, and within eight hours, the host cell releases hundreds of new virus particles to infect other cells.
Click to reveal this step.
Explain to students that the deadly disease called acquired immune deficiency syndrome (AIDS) is caused by an RNA virus called human immunodeficiency virus (HIV). HIV belongs to a group of RNA viruses that are called retroviruses. The genetic information of a retrovirus is copied from RNA to DNA instead of from DNA to RNA.
Step students through the process of an HIV infection.
Tell students: When a retrovirus infects a cell, it makes a DNA copy of its RNA.
Click to reveal this step.
Tell students: Then, the viral DNA is inserted into the host cell.
Click to reveal this step.
Explain that retroviral infections are similar to lysogenic infections of bacteria. Much like a prophage in a bacterial host, the viral DNA may remain inactive for many cell cycles before making new virus particles and damaging the cells of the host’s immune system. Eventually, the DNA is transcribed and new viral parts are made.
Click to highlight this step.
Tell students: Once activated, the viruses leave the cell and begin to destroy the very system of the body that would normally fight infection.
Click to highlight this step.
Tell students: The word retro means “backward.”
Ask: Why is the word retrovirus used to describe HIV?
Answer: The genetic information of a retrovirus like HIV is copied from RNA to DNA instead of from DNA to RNA.
Ask: If the virus that causes the common cold is also an RNA virus, why is it not called a retrovirus?
Answer: In a cell infected with the common cold virus, RNA is not copied to make DNA. Instead, the viral RNA is translated by the cell’s ribosomes to produce viral proteins.
Remind students that viruses must infect living cells to grow and reproduce, taking advantage of the nutrients and cellular machinery of their hosts. This means that all viruses are parasites.
Explain that, despite the fact that they are not alive, viruses have many of the characteristics of living things. After infecting living cells, viruses can reproduce, regulate gene expression, and even evolve.
Direct students to compare the principal differences between cells and viruses that are shown in the table.
Ask: Based on this information, would you classify viruses as living or nonliving? Explain.
Sample answer: I would classify viruses as nonliving, because they cannot grow, develop, or obtain energy, and because they cannot reproduce independently.
Lead students in a short discussion of viruses. Review with students the key points of this lesson.
Remind them that viruses can reproduce only by infecting living cells.
Click to reveal this bullet point.
Tell students: Inside living cells, viruses use their genetic information to reproduce. Some replicate immediately. Others remain inactive for a period of time within the host.
Click to reveal this bullet point and the image of lysogenic and lytic infection cycles.
Ask for a volunteer to properly label the virus infection cycles.
Click to reveal the correct answers.
Remind students that they should have been using the worksheet to record the similarities and differences between viruses and cells throughout the lesson.
Give students time to work individually or in small groups to review their notes and add to them as necessary. Return to Slide 12 if students need to see a summary of the key points.
Worksheet Answers:
In the center of the Venn diagram should be two key points:
The genetic code of both can contain DNA and both have the ability to change over time.
In the Virus side of the Venn diagram should be the following:
Structure: DNA or RNA in capsid, some with envelope
Reproduction: Only within a host cell
Genetic Code: DNA or RNA
Growth and Development: No
Obtain and Use Energy: No
Response to Environment: No
In the Cell side of the Venn diagram should be the following:
Structure: Cell membrane, cytoplasm; eukaryotes also contain nucleus and many organelles
Reproduction: Independent cell division, either asexually or sexually
Growth and Development: Yes; in multicellular organisms, cells increase in number and differentiate
Obtain and Use Energy: Yes
Response to Environment: Yes