Viruses and Bacteria

Viruses and Bacteria

High School

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Learning Objectives

• Describe the characteristics, shapes, and habitats of bacteria.

• Describe virus structure and why they are considered non-living.

• Compare bacteria and viruses based on size, structure, and reproduction.

• Explain the lytic and lysogenic cycles of viral replication.

Key Vocabulary

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Bacteria

Tiny, single-celled living microorganisms found everywhere, including in soil, water, and even inside our bodies.

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Virus

A non-living infectious agent, smaller than bacteria, that can only replicate inside a host cell.

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Host Cell

A living cell that a virus invades and uses as a machine to replicate itself.

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Capsid

The protective outer protein shell of a virus that encloses its genetic material, like DNA or RNA.

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Lytic Cycle

A viral replication process that creates new viruses and results in the destruction of the host cell.

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Lysogenic Cycle

A viral replication process where the virus's DNA integrates into the host cell's DNA, remaining dormant.

The Three Main Shapes of Bacteria

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Cocci (Spheres)

• ​Cocci bacteria are characterized by their spherical or round shape.

• ​​They can be found in pairs, chains, or bunched in clusters.

• ​*Staphylococcus* is an example of a common cocci bacterium species.

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Bacilli (Rods)

• ​Bacilli bacteria can be identified by their distinctive rod-like shape.

• ​​These bacteria can appear as single rods or be joined in chains.

• ​*Escherichia coli* (*E. coli*) is a well-known example of bacilli.

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Spirilla (Spirals)

• ​Spirilla are a type of bacteria that have a spiral shape.

• ​​Their unique corkscrew-like form helps them move around very effectively.

• ​An example is *Spirillum volutans*, which is found in fresh water.

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Solved Example 1
If a single bacterium measures 2 micrometers and a virus measures 100 nanometers, how many times larger is the bacterium than the virus? (1 micrometer = 1000 nanometers)

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Step 1: Analyze and Sketch the Problem

• Goal: Find how many times larger a bacterium is than a virus.

• Knowns: Bacterium length = 2 micrometers, Virus length = 100 nanometers.

• Unknown: The ratio of the bacterium's size to the virus's size.

• Conversion: 1 micrometer = 1000 nanometers.

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Solved Example 1
If a single bacterium measures 2 micrometers and a virus measures 100 nanometers, how many times larger is the bacterium than the virus? (1 micrometer = 1000 nanometers)

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Step 2: Solve for the Unknown

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Solved Example 1
If a single bacterium measures 2 micrometers and a virus measures 100 nanometers, how many times larger is the bacterium than the virus? (1 micrometer = 1000 nanometers)

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Step 3: Evaluate the Answer

• The bacterium is 2000 nm long and the virus is 100 nm long.

• Since 2000 is 20 times 100, the conclusion that the bacterium is 20 times larger than the virus is reasonable.

Multiple Choice

Which of the following are the three main shapes used to classify bacteria?

• Circles, squares, and ovals

• Cocci, bacilli, and spirilla

• Rods, spirals, and triangles

• Spheres, cubes, and pyramids

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The Vital Role of Bacteria

• Most bacteria are harmless; some help us digest food and fight infections.

• ​They act as decomposers, breaking down dead material into essential nutrients.

• Bacteria are also used to produce many foods like yogurt and cheese.

• Washing hands and consuming clean food helps prevent harmful bacterial infections.

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Multiple Choice

According to the slide, which of the following is a beneficial role of bacteria?

• Turning clean water into contaminated water

• Only living in extreme environments

• Causing all infections in humans

• Helping to make foods like yogurt and cheese

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What are Viruses?

• A virus is a small infectious agent with DNA or RNA in a protein coat.

• Considered non-living, they are not cells and are much smaller than bacteria.

• They must infect a living host cell to reproduce and make more copies.

• This process often causes diseases as viruses can change to evade the immune system.

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Solved Example 2
A single drop of blood has a volume of 0.05 mL and can hold five billion viruses. How many viruses could fit in a 1-liter bottle of blood?

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Step 1: Analyze and Sketch the Problem

• Goal: Find the total number of viruses in 1 liter of blood.

• Knowns: Viruses per drop = 5,000,000,000; Volume of a drop = 0.05 mL; Total volume = 1 L.

• Unknown: Total number of viruses.

• Formula: Total Viruses = (Viruses per drop / Volume of a drop) × Total Volume.

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Solved Example 2
A single drop of blood has a volume of 0.05 mL and can hold five billion viruses. How many viruses could fit in a 1-liter bottle of blood?

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Step 2: Solve for the Unknown

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Solved Example 2
A single drop of blood has a volume of 0.05 mL and can hold five billion viruses. How many viruses could fit in a 1-liter bottle of blood?

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Step 3: Evaluate the Answer

Multiple Choice

Why is a virus considered non-living?

• It is larger than a bacterium.

• It cannot reproduce or metabolize energy on its own.

• It is made of cells.

• It does not contain DNA or RNA.

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The Basic Structure of a Virus

• All viruses have genetic material with instructions to create more new viruses.

• ​A protein shell called a capsid protects the genetic material of the virus.

• The shape of the capsid determines the overall shape of the virus.

• Some viruses have an envelope with surface markers for attaching to host cells.

Multiple Choice

What are the two essential features found in all viruses?

• Genetic material and a capsid

• A nucleus and surface markers

• A capsid and an envelope

• DNA and an envelope

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Viral Replication Cycles

Lytic Cycle

• ​This is a fast replication process where the virus immediately creates new viruses.

• ​​The production of new viruses causes the host cell to burst, or lyse.

• ​This process kills the host cell and causes symptoms of the illness to appear quickly.

Lysogenic Cycle

• ​This is a slow process where the virus remains dormant inside the host cell.

• ​​Viral DNA integrates into the host DNA and is copied when the cell divides.

• ​The virus can remain hidden for a long time before it becomes active.

Multiple Choice

What is the key difference between the lytic and lysogenic cycles?

• The lytic cycle results in the immediate death of the host cell, while the lysogenic cycle involves a dormant period where the viral DNA hides.

• The lytic cycle is slow and dormant, while the lysogenic cycle is fast and immediately kills the host cell.

• The lysogenic cycle involves the host cell bursting, while the lytic cycle involves the viral DNA integrating into the host DNA.

• Only the lytic cycle requires a host cell for replication.

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Viruses and Your Health

Treating Viruses

• ​Antibiotics are powerful medicines for bacterial infections, but they are ineffective against viruses.

• ​​Once you are infected, you can typically only treat the symptoms of the viral illness.

• ​Your own immune system must work to fight off the virus and clear the infection.

Prevention with Vaccines

• ​Vaccines introduce a weakened or inactive part of a virus to your immune system.

• ​​This allows your body to build special proteins, called antibodies, without causing the disease.

• ​These antibodies provide long-term protection if you are exposed to the actual virus later.

Multiple Choice

How do vaccines work to protect you from viral diseases?

• They are a type of antibiotic that kills viruses directly.

• They cure the symptoms of a viral infection after you get sick.

• They train your immune system to build antibodies against a virus without causing disease.

• They use helpful bacteria to fight off invading viruses.

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Common Misconceptions about Microbes

Misconception	Correction
All bacteria are bad and cause disease.	Most bacteria are harmless or helpful, aiding digestion and nutrient cycling.
Viruses are a type of living cell.	Viruses are non-living and need a host cell to reproduce.
Antibiotics can cure the flu or a common cold.	Antibiotics only treat bacterial infections, not viral illnesses like the flu.

Multiple Choice

Which statement best distinguishes viruses from bacteria?

• Bacteria are living cells that can reproduce on their own, while viruses are non-living and require a host to replicate.

• Viruses and bacteria are both non-living infectious agents.

• Bacteria are non-living, while viruses are living cells.

• Viruses are living, single-celled organisms, while bacteria are non-living particles.

Multiple Choice

Why is a host cell critical for a virus to reproduce, but not for a bacterium?

• Because bacteria do not reproduce, while viruses do.

• Because bacteria have their own cellular machinery for metabolism and reproduction, while viruses do not.

• Because viruses live in colonies, while bacteria live inside host cells.

• Because host cells provide a protective envelope for bacteria, which viruses do not need.

Multiple Choice

A patient experiences a sudden onset of symptoms from a viral infection. Based on this, which replication cycle is the virus most likely undergoing and why?

• The lytic cycle, because the viral DNA integrates with the host cell DNA, causing immediate symptoms.

• The lytic cycle, because it involves the rapid production of new viruses and the destruction of host cells.

• The lysogenic cycle, because it quickly produces a large number of viruses.

• The lysogenic cycle, because it is a dormant phase that hides from the immune system.

Multiple Choice

Which statement best describes the relationship between vaccines, antibodies, and the prevention of a viral disease like smallpox?

• Antibodies are a type of virus used in vaccines to prevent diseases like smallpox.

• Vaccines introduce antibodies to the body, which immediately fight off any future smallpox infection.

• Vaccines directly destroy the smallpox virus, and antibodies clean up the remains.

• Vaccines trigger the immune system to produce its own antibodies against the smallpox virus, providing long-term memory and protection.

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Summary

• Bacteria are diverse, single-celled organisms found everywhere in various shapes.

• Viruses are non-living infectious agents that need a host cell to replicate.

• All viruses have genetic material and a capsid; some also have an envelope.

• Viruses replicate through the lytic (fast) or lysogenic (slow) cycles.

• Pathogens are harmful bacteria or viruses that can cause various illnesses.

• Good hygiene and vaccines help prevent bacterial and viral diseases, respectively.

Poll

On a scale of 1-4, how confident are you with the concepts of viruses and bacteria covered today?

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