Viruses

What are viruses?

* Tiny (only seen on an electron microscope)
* Obligate parasites (need a host to reproduce)
* Classified by their shape
* Are considered to be living and non-living

Describe the structure of a virus

1. Capsid (protein coat): protects the virus
2. Nucleic Acid: DNA or RNA
* no organelles
* no metabolic machinery

What are the arguments for viruses being both __living__ and __non-living__?

__Living:__

* A virus contains genetic material
* Contains a protein coat
* Can replicate (though requires a host)

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__Non-Living:__

* Non-cellular
* Cannot reproduce by themselves
* No cell organelles
* Only have one type of nucleic acid

Why is a virus described as an “obligate parasite”?

* They need a host to reproduce

How are viruses classified?

Viruses are classified according to their shape:


1. Round (ex. influenza)
2. Rod-shaped (ex. Tobacco Mosaic)
3. Complex (ex. bacteriophage)

Why are antibiotics ineffective against viruses?

1. antibiotics target bacteria
2. antibiotics target cell organelles, a virus doesn’t have any

Viral Replication. How do viruses replicate?

* Viruses are obligate parasites- need a host to reproduce ex. bacteriophage is a virus that infects bacteria to replicate.
* There are 5 stages of replication

List the 5 stages in Virus Replication

1. Attachement
2. Entry
3. Synthesis
4. Assembly
5. Release

List and explain the stages of Viral Replication

1. __Attachement:__ Virus attaches to host (bacteria)
2. __Entry:__ Virus makes a hole in bacteria cell wall and injects nucleic acid (DNA or RNA)
3. __Synthesis:__ Host DNA is made inactive, viral DNA uses bacteria organelles to produce new viral nucleic acid and proteins
4. __Assembly:__ New viruses are made inside the infected cell.
5. __Release:__ Bursting of cell (lysis) occurs releasing thousands of viruses.

What is lysis?

__Bursting of a cell__, which causes the release of thousands of viruses. Occurs during the release stage of viral replication.

Attachement stage of viral replication

1. __Attachement:__ Virus attaches to host (bacteria)

Entry stage of viral replication

2. __Entry:__ Virus makes a hole in bacteria cell wall and injects nucleic acid (DNA or RNA)

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Synthesis stage of viral replication

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3. __Synthesis:__ Host DNA is made inactive, viral DNA uses bacteria organelles to produce new viral nucleic acid and proteins

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Assembly stage of viral replication

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4. __Assembly:__ New viruses are made inside the infected cell.

Release stage of viral replication

5. __Release:__ Bursting of cell (lysis) occurs releasing thousands of viruses.

Acronym for stages in viral replication

RASEA- reversed


1. __Attachement:__ Virus attaches to host (bacteria)
2. __Entry:__ Virus makes a hole in bacteria cell wall and injects nucleic acid (DNA or RNA)
3. __Synthesis:__ Host DNA is made inactive, viral DNA uses bacteria organelles to produce new viral nucleic acid and proteins
4. __Assembly:__ New viruses are made inside the infected cell.
5. __Release:__ Bursting of cell (lysis) occurs releasing thousands of viruses.

What are virus disadvantages?

disease…duh.

3 examples of human diseases caused by viruses

1. Influenza
2. AIDs
3. Mumps

2 examples of plant diseases caused by viruses

1. Potato mosaic disease
2. Tobacco mosaic disease

2 examples of animal diseases caused by viruses

1. Foot and mouth
2. Rabies

Give an example of 2 virus benefits

1. Genetic Engineering
2. Infection Control

How is Infection Control beneficial?

bacteriophages can be used to control bacterial infections which may reduce the number of antibiotic-resistant bacteria

How is Genetic Engineering beneficial?

Transfer of genes using viruses e.g vectors

Explain why viruses are described as obligate parasites

They require a host to reproduce

Explain in detail the term vaccination

Vaccination is a non disease causing dose of a disease. It is a form of artificial active immunity and it is long lasting since the body is learning how to produce the antibodies itself.

Name a harmful virus, other than Cov-2

mumps, aids, influenza

From which biochemical component are viral coats made?

protein

Name the main chemical component of a virus

nucleic acid

Immunity is the ability to resist infection. Name two types of induced immunity

1. Passive Immunity
2. Active immunity

Which type of immunity occurs after a vaccination?

active

Give one difference between the types of induced immunity

1. Active immunity- long lasting
2. Passive immunity- short term

Discuss the statement: “Viruses are not considered to be living organisms”

* They are obligate parasites-cannot reproduce independently
* They contain no organelles and no metabolic mechanisms
* They are made of only one type of nucleic acid

What is the main constituent of a capsid coat?

protein

What virus causes disease in plants?

Tobacco mosaic virus

How to distinguish between viruses?

shape

Give one way in which viruses are metabolically important.

Biotechnology and genetic engineering- transfer of genes using viruses

DISCUSS THE STATEMENT “VIRUSES ARE NOT CONSIDERED TO BE LIVING”

* Viruses have __**some features**__ of living things, e.g. containing RNA or DNA, being able to replicate and having a protein coat.


* However, other characteristics of living things are missing, e.g. viruses are non-cellular and **cannot reproduce** on their own. Viruses do not have cell organelle and **only contain one kind** of nucleic acid while most living things have both RNA and DNA. 

**DESCRIBE HOW THE VIRUS REPLICATES** 

1. Virus attaches to a host cell and inserts its nucleic acid into the cell cytoplasm. 
2. The viral enzyme __destroys the host cell’s nucleus__
3. The virus uses host cell’s machinery to make more viral dna and protein coats 
4. New viruses are assembled and burst out of the host to infect other cells

**GIVE ONE EXAMPLE OF A BENEFICIAL VIRUS**

Bacteriophages can be used to control bacterial infections

**WHY ARE VIRUSES DIFFICULT TO CLASSIFY INTO A KINGDOM?**

Because they are not made up of cells and are unable to carry out metabolic reactions on their own.

**HOW DO SCIENTISTS DISTINGUISH BETWEEN DIFFERENT VIRUSES**

According to their shape, round, rod or complex