Viruses (SAQs)

Botany-2 | 8. Viruses – SAQs:
Welcome to “SAQs” in “Chapter 8: Viruses”. This page includes the most important FAQs from previous exams. Each answer is provided in simple English, followed by a Telugu explanation, and then presented in the exam format. This approach helps you prepare effectively and aim for great results in your final exams.

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SAQ-1 : What is ICTV? How are viruses named?

Introduction

In the field of virology, understanding how viruses are named and classified is essential. The International Committee on Taxonomy of Viruses (ICTV) plays a central role in this process, providing a structured system that helps scientists around the world identify and categorize viruses. Just like how every place has a name and an address to identify it, viruses also need a systematic way to be recognized, especially when studying diseases that impact human health.

Role of ICTV in Virus Classification and Naming

1. ICTV’s Hierarchical System: The ICTV is responsible for overseeing the classification and naming of viruses. It uses a hierarchical system that includes different levels such as family, genus, and species. This system is like a family tree that helps in understanding the relationships between different viruses. For example, the family name of a virus ends with the suffix “-Viridae,” which tells us it belongs to a larger group of related viruses. The genus name ends with “-virus,” indicating a more specific category within the family.
2. Species Naming Conventions: When it comes to species names, these are often common terms in English that describe the virus’s characteristics. For instance, the virus that causes Acquired Immunodeficiency Syndrome (AIDS) in humans is classified under the family Retroviridae and the genus Lentivirus. Its species name is the Human Immunodeficiency Virus (HIV). This naming system helps scientists and healthcare professionals communicate more effectively, ensuring everyone understands exactly which virus is being discussed.
3. Naming Based on Disease: Sometimes, viruses are named based on the diseases they cause. A well-known example is the Poliovirus, which is named after the disease Polio. This method of naming makes it easier for people to associate the virus with the illness it causes, aiding in public awareness and understanding.

Summary

In conclusion, the International Committee on Taxonomy of Viruses (ICTV) plays a crucial role in the naming and classification of viruses. By using a systematic approach, ICTV ensures that viruses are identified in a consistent and structured manner, which is essential for scientific research, global health communication, and disease control. Whether it’s understanding the family and genus of a virus or recognizing a virus by the disease it causes, this naming system is vital for everyone involved in virology, from students to researchers.

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SAQ-2 : Explain the chemical structure of viruses.

Introduction

Viruses, though tiny and invisible to the naked eye, are fascinating in their complexity. They may vary in shape and size, but their basic structure remains consistent. Each virus is made up of two primary components: a core and a capsid. To understand how viruses function and how they cause diseases, it’s essential to grasp the basic chemical structure that makes them what they are.

The Core and Capsid: The Building Blocks of Viruses

1. The Core and Genome: At the heart of every virus lies its core, which contains the virus’s genetic material or genome. This genetic material is what allows the virus to replicate and spread. Depending on the type of virus, the core may contain different forms of nucleic acids. These can include single-stranded DNA (ssDNA), double-stranded DNA (dsDNA), single-stranded RNA (ssRNA), or double-stranded RNA (dsRNA). For example, some plant viruses have ssRNA, while many viruses that infect animals, including humans, have dsDNA.
2. The Capsid and Its Structure: Surrounding the core is a protective shell known as the capsid. This capsid is made up of proteins and gives the virus its shape, while also protecting the genetic material inside. The capsid itself is composed of smaller protein units called capsomeres. These capsomeres fit together like pieces of a puzzle, forming the overall structure of the virus. The number and arrangement of these capsomeres can vary from one virus to another, which is why different viruses can look so distinct under a microscope.
3. The Nature of Viral Nucleic Acids: The nucleic acid inside a virus can be either circular or linear. This structural variation helps determine how the virus interacts with the cells it infects. Some viruses contain just one piece of nucleic acid, while others, like the Human Immunodeficiency Virus (HIV), have more than one. For instance, HIV carries two identical RNA molecules, making its structure a bit more complex.

Summary

To sum up, the chemical structure of viruses is a fundamental concept in virology. Each virus consists of a core that contains its genetic material and a capsid that protects and shapes it. The type of nucleic acid and the structure of the capsid are key elements that determine how a virus behaves and how it can be studied. By understanding these basic components, we can better comprehend how viruses function and how they can be controlled, especially in the context of diseases that affect plants, animals, and humans.

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SAQ-3 : Explain the structure of TMV.

Introduction

The Tobacco Mosaic Virus (TMV) is a well-known virus that primarily infects tobacco plants. It gets its name from the mosaic-like pattern it creates on infected leaves, which is one of its most recognizable symptoms. Beyond its impact on plants, TMV is also famous for its unique and complex structure, making it a key subject of study in virology.

The Structure of TMV: A Closer Look

1. TMV: A Single-Stranded RNA Virus: One of the defining features of TMV is its genetic material, which consists of single-stranded RNA (ssRNA). This RNA is tightly coiled within the virus and contains about 6,500 nucleotides—the building blocks of RNA. This genetic material is what the virus uses to replicate itself once it infects a plant cell, spreading the infection.
2. Size and Shape of TMV: TMV has a distinct rod-like shape that sets it apart from other viruses. It measures approximately 300 nanometers (nm) in length and 18 nm in diameter. To put this in perspective, a nanometer is one-billionth of a meter, making TMV incredibly small yet complex. The virus’s overall molecular weight is about 39 million Daltons, a unit of measurement used in molecular biology to express the size of molecules.
3. The Capsid and Capsomeres: Surrounding the RNA core of TMV is a protein coat known as the capsid. This capsid is essential for protecting the RNA and giving the virus its structure. The capsid is made up of 2,130 protein subunits called capsomeres. These capsomeres are arranged in a helical pattern, forming a spiral that wraps around the RNA core. Inside this helical structure is a central hollow core that measures about 4 nm in diameter, adding to the virus’s distinctive appearance.
4. Amino Acids in Capsomeres: Each of the capsomeres in TMV is made up of 158 amino acids. Amino acids are the fundamental building blocks of proteins, and in the case of TMV, they are crucial for constructing the protective capsid. This complex arrangement of proteins not only protects the virus but also helps it attach to and infect plant cells.

Summary

In summary, the Tobacco Mosaic Virus is a fascinating example of viral structure, characterized by its rod-like shape, single-stranded RNA core, and the intricate arrangement of protein capsomeres that form its protective coat. Understanding the structure of TMV is essential for studying how it infects plants and for developing strategies to combat its effects on agriculture. This knowledge also provides insight into the broader field of virology, where the study of virus structures like TMV continues to be a critical area of research.

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SAQ-4 : Explain the structure of T-even bacteriophages.

Introduction

Bacteriophages, especially the T-even bacteriophages, are fascinating viruses that specifically infect bacteria. Their unique structure has made them an important topic of study in science, helping us understand how viruses interact with their bacterial hosts.

The Structure of T-even Bacteriophages

1. What are Bacteriophages?
   Bacteriophages, often referred to as ‘phages’, are viruses that target and infect bacteria. These viruses have a tadpole-like shape, which makes them easily recognizable. The structure of a T-even bacteriophage is complex, with each part playing a crucial role in its ability to infect bacterial cells.
2. The Head of T-even Bacteriophages: One of the most noticeable features of T-even bacteriophages is their hexagonal head. This head is not just a simple shape; it is capped with a smaller hexagonal pyramid on top, which adds to its unique appearance. Inside this head lies the virus’s genetic material, which is responsible for taking over the host bacterium’s functions once the virus injects its DNA.
3. The Tail Structure: Extending from the head is the tail structure, which is a vital component of the bacteriophage. This tail acts as a syringe, injecting the viral DNA into the bacterial cell. The tail itself is made up of several parts, including the tail sheath, base plate, pins, and tail fibers. These components work together to ensure that the virus can effectively attach to the bacterium and deliver its genetic material.
4. The Collar: Connecting the head to the tail is a collar. This collar acts as a bridge between these two major parts of the bacteriophage, ensuring that they work together seamlessly during the infection process.
5. Tail Plate and Tail Fibers: At the end of the tail is a hexagonal tail plate, which is equipped with six tail pins and tail fibers. The tail fibers are particularly important because they allow the virus to attach securely to the bacterial cell. Once attached, the tail pins help the virus penetrate the bacterial cell wall, beginning the infection process.

Summary

In conclusion, T-even bacteriophages are remarkable viruses with a highly specialized structure. They feature a hexagonal head that houses their genetic material, a complex tail structure that delivers this material into the host, and a collar that connects these parts. The tail plate and tail fibers play crucial roles in attaching the virus to the bacterial cell and initiating the infection. Understanding the intricate structure of these bacteriophages is essential for comprehending how they operate and their significance in the study of bacterial infections.

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SAQ-5 : Explain the lytic cycle with reference to certain viruses.

Introduction

The lytic cycle is an essential process through which certain viruses reproduce, leading to the destruction of the host cell and the release of new viruses. This cycle is particularly common in virulent phages, a type of virus that aggressively targets and destroys bacterial cells. Understanding the lytic cycle helps us grasp how viruses spread and cause infections.

The Lytic Cycle Explained

What is the Lytic Cycle?

The lytic cycle is a key method of viral reproduction where a virus takes over a host cell’s machinery to produce new virus particles, ultimately leading to the rupture (lysis) of the host cell and the release of new viruses. This cycle involves several stages, each playing a crucial role in the viral life cycle.

1. Attachment Stage: The lytic cycle begins when the virus attaches itself to a specific host cell. Imagine this stage as a virus finding and locking onto a door handle of the host cell. The virus uses its tail fibers to grip onto specific receptor sites on the surface of the host cell. This attachment is crucial because it sets the stage for the virus to inject its genetic material into the cell.
2. Penetration Stage: After successfully attaching to the host cell, the virus injects its genetic material—either DNA or RNA—into the cell. You can think of this as the virus acting like a syringe, piercing through the host cell’s outer wall and injecting its contents inside. Once the genetic material is inside, the outer shell of the virus, known as a ‘ghost’, remains outside the host cell.
3. Biosynthesis Stage: Once inside, the viral genetic material hijacks the host cell’s machinery to start producing viral components. This stage is like a factory being taken over to produce parts needed to build new viruses. The host cell begins to create viral DNA, enzymes, and protein shells (capsids) that will eventually form new viruses. However, at this stage, these components are not yet fully assembled into complete viruses.
4. Maturation Stage: In the maturation stage, all the newly synthesized viral components come together to form complete virus particles, known as virions. This is like assembling a product on a factory line, where all the parts come together to create the final product. During this time, known as the ‘eclipse period’, the host cell is full of these incomplete viral particles, which gradually mature into infectious viruses.
5. Release Stage: The final stage of the lytic cycle involves the destruction of the host cell. The virus produces an enzyme called lysozyme, which breaks down the host cell’s wall, causing it to burst open. Imagine this as a balloon popping and releasing all the air inside—in this case, the host cell bursts, releasing all the newly formed viruses into the surrounding environment, where they can go on to infect other cells.

Summary

In summary, the lytic cycle is a vital process for the reproduction of virulent phages and other viruses. It involves a series of stages: attachment, penetration, biosynthesis, maturation, and release. Each stage is critical in the life cycle of the virus, leading to the destruction of the host cell and the spread of new viruses. Understanding this cycle not only provides insights into how viruses multiply but also informs the development of antiviral treatments aimed at disrupting this process.