Virus - An Introduction
We are all aware of the pandemic caused by the coronavirus. It is not easy to kill viruses. Have you ever thought about why it is very difficult to destroy viruses? Viruses keep on changing their genetic material. That's why it is very difficult to make vaccines to kill viruses. To know more about plant and animal viruses and the difference between them, continue reading.
What is a Plant Virus?
Plant viruses are the viruses that infect plants and these are obligatory viruses that mean they can't replicate or reproduce without the host. As viruses do not have cellular machinery they use the machinery of plant cells to replicate and reproduce.
Structure of Plant Viruses
Viruses are made up of two components: proteins and genetic material. Protein subunits are placed around the circumference of the circle to form a disc. Then these discs are stacked around the genetic material of the virus and form a complete virus.
There are various shapes of plant viruses but most of the viruses are rod-shaped. And the length of these viruses is between 300-500nm. Isometric is the second most common shape of the plant virus. These types of viruses may have a double protein coat that is associated to form an icosahedral-shaped part. Very few plant viruses may have a lipid coat. The genetic material of plant viruses may be double or single-stranded DNA. But in most cases, single-stranded RNA is the genetic material of plant viruses.
Examples of Plant Viruses
An example of plant viruses that have double-stranded DNA as genetic material is the cauliflower mosaic virus. Bean golden mosaic virus is a plant virus that has single-strand DNA as genetic material. The tobacco mosaic virus is a plant virus that has single-stranded RNA as the material.
What is an Animal Virus?
The animal virus is a virus that infects animals and other viruses. This virus is also unable to replicate outside the animal body or animal cell. Animal viruses are also made of two components: protein and genetic material. The protein coat is known as capsid and genetic material is present inside it. Animal viruses also have an envelope made of lipids.
There are various shapes of animal viruses, such as helical and icosahedral. The shape of the Ebola virus is long like a thread. The genetic material of animal viruses is made of double-stranded DNA or RNA, single-stranded DNA or RNA. They used to cause various types of diseases in animals and humans. Herpesvirus and poxvirus are viruses made of double-stranded DNA.
Examples of Animal Virus
The genetic material of hepatitis B, herpes, and pox virus is double-stranded DNA. The genetic material of parvovirus is single-stranded DNA. Picornavirus is a single-stranded RNA virus. R reovirus is a double-stranded RNA virus.
Difference between Plant Viruses and Animal Viruses
Important Questions
Q1. What are animal virus infections called?
Ans: Infections that occur through animal viruses are called zoonotic or viral zoonoses. Examples are rabies and yellow fever.
Q2. What are the main characteristics of plant viruses?
Ans: The most common shape of a plant virus is a rod shape with a protein disc forming a tube around the viral genome.
Q3. Are viruses living or nonliving?
Ans: Viruses are not made of cells so they can't be considered living but they are not also dead because they replicate inside the host cell.
Conclusion
In conclusion, we learnt that viruses are infectious microbes that are made of protein and genetic material. Plant and animal viruses cause infection in plants and animals, respectively. We have also studied a table listing the differences between plants and animal viruses. We hope to have helped you with your queries. You can go through the important and practise questions to test your knowledge as well the following links for further readings.
FAQs on Difference Between Plant Virus and Animal Virus
1. What are the main differences between a plant virus and an animal virus?
The primary differences between plant and animal viruses relate to their structure, genetic material, and mode of transmission. Key distinctions include:
- Genetic Material: Most plant viruses contain single-stranded RNA (ssRNA), while animal viruses can have ssRNA, double-stranded RNA (dsRNA), single-stranded DNA (ssDNA), or double-stranded DNA (dsDNA).
- Structure: Plant viruses are typically simpler, often rod-shaped (helical) or icosahedral, and lack a lipid envelope. Animal viruses are more complex and can be enveloped, which they acquire from the host cell membrane.
- Mode of Entry: Plant viruses cannot penetrate the rigid plant cell wall on their own. They require a wound or are transmitted by vectors like insects. Animal viruses enter host cells through specific surface receptors via processes like endocytosis or membrane fusion.
- Transmission: Plant viruses spread through vectors (insects, fungi), pollen, or seeds. Animal viruses spread through direct contact, respiratory droplets, bodily fluids, or vectors.
2. What are the fundamental characteristics of any virus?
Viruses are non-cellular, infectious agents that are considered to be on the boundary of living and non-living. Their key characteristics are:
- They are obligate intracellular parasites, meaning they can only replicate inside a living host cell.
- They possess genetic material, either DNA or RNA, but never both.
- Their genetic material is enclosed in a protective protein coat called a capsid.
- They lack their own cellular machinery for metabolism or protein synthesis and hijack the host cell's machinery to multiply.
- Outside the host, they exist as inert, crystalline structures called virions.
3. Can you provide some common examples of diseases caused by plant and animal viruses?
Certainly. Viruses cause a wide range of diseases in both plants and animals.
- Examples of Plant Viral Diseases: Tobacco Mosaic Disease (caused by Tobacco Mosaic Virus), Tomato Spotted Wilt, Potato Leaf Roll, and Cauliflower Mosaic Disease.
- Examples of Animal Viral Diseases: Influenza (caused by Influenza virus), AIDS (caused by HIV), Rabies, Polio, COVID-19 (caused by SARS-CoV-2), and Hepatitis.
4. Why do plant and animal viruses need different methods to enter a host cell?
The different entry methods are dictated by the fundamental structural differences between plant and animal cells. A plant cell is protected by a rigid cell wall made of cellulose, which acts as a strong physical barrier. A virus cannot simply fuse with or be engulfed through this wall. Therefore, plant viruses rely on mechanical damage to the plant—caused by insects, pruning, or weather—to gain entry. In contrast, an animal cell is enclosed by a flexible plasma membrane. Animal viruses have evolved surface proteins that bind to specific receptors on this membrane, allowing them to enter through mechanisms like membrane fusion or endocytosis, a process where the cell actively engulfs the virus.
5. How does the structure of a plant virus like Tobacco Mosaic Virus (TMV) compare to an animal virus like Influenza?
The structural comparison highlights key adaptations to their respective hosts. Tobacco Mosaic Virus (TMV) has a simple, rigid, rod-like shape with a helical symmetry. Its genetic material (RNA) is coiled within a capsid made of repeating protein subunits. It is a 'naked' virus, meaning it lacks an outer lipid envelope. On the other hand, the Influenza virus is roughly spherical and has a more complex structure. Its genetic material is segmented RNA, and its capsid is enclosed within a lipid envelope derived from the host cell. This envelope is studded with viral proteins like hemagglutinin (HA) and neuraminidase (NA), which are crucial for attaching to and entering animal cells.
6. Can a plant virus infect an animal, or vice versa? Explain why.
No, a plant virus cannot infect an animal, and an animal virus cannot infect a plant. This is due to the principle of host specificity. Viruses have evolved to recognise and bind to very specific receptor molecules on the surface of their host cells. These receptors are unique to certain species or cell types. A plant virus's surface proteins do not match the receptors on an animal cell membrane, and vice versa. Without this precise molecular 'handshake', the virus cannot attach to and enter the cell to begin replication.
7. How are viruses generally classified?
Viruses are classified based on several criteria, most importantly:
- Type of Genetic Material: This is the primary basis, distinguishing between DNA viruses and RNA viruses. This is further broken down into single-stranded (ss) or double-stranded (ds).
- Host Organism: Viruses are grouped based on the type of host they infect, such as plant viruses, animal viruses, or bacteriophages (viruses that infect bacteria).
- Structure of Capsid: Viruses are also classified by their shape, such as helical, icosahedral (polyhedral), or complex.
- Presence or Absence of an Envelope: They are categorised as either enveloped or non-enveloped (naked) viruses.
8. What is the key difference between a virus and a viroid?
The key difference lies in their composition. A virus is composed of genetic material (DNA or RNA) enclosed within a protective protein coat (capsid). A viroid is even simpler and more minimalistic; it is an infectious agent that consists only of a short, circular, single-stranded RNA molecule with no protein coat. Viroids are known to cause diseases primarily in plants.
