Viruses and Prokaryotes - PC\|MAC

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Viruses and Prokaryotes

Cellular Basis of Life Q: Are all microbes that make us sick made of living cells?

Chapter Summary

The diagram below shows what you will read about in this chapter and how the chapter is organized. Study the diagram. Then answer the questions that follow.

20.1 Viruses

The discovery of viruses Viral infections

20.2 Prokaryotes

Classifying prokaryotes Structure and function The importance of prokaryotes

20.3 Diseases Caused by Bacteria and Viruses

Bacterial diseases Viral diseases

Emerging diseases

1. What do you think you will learn about in this chapter? viruses, prokaryotes, and the

diseases they cause

2. In which lesson do you expect to learn more about how viruses cause disease? Lesson 3

3. What do you think is meant by "emerging diseases"? Sample answer: diseases that are new

4. Predict two things you will learn about in Lesson 3. Sample answer: bacterial diseases

and viral diseases

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20.1 Viruses

Lesson Objectives

Explain how viruses reproduce. Explain how viruses cause infection.

BUILD Vocabulary

A. The chart below shows key terms from the lesson with their definitions. Complete the chart by writing a strategy to help you remember the meaning of each term. One has been done for you.

Term Bacteriophage Capsid Lysogenic infection

Lytic infection

Prophage

Retrovirus

Virus

Definition

How I'm Going to Remember the Meaning

A virus that infects bacteria

Phage sounds like "fight"; bacteriophages fight bacteria.

The protein coat surrounding a virus

A capsid is like a cap that covers your head.

Infection in which a virus inserts its nucleic acid into the DNA of the host cell and is duplicated with the cell's DNA

Think lyso = lie-so. The virus lies to the cell so it can regenerate itself for generations.

An infection in which a virus enters a bacterial cell, makes copies of itself, and causes the cell to burst, or lyse

A lytic infection is like a ticking time bomb that causes the cell to "blow up."

Bacteriophage DNA that is inserted into the bacterial host's DNA

The prophage virus is a real pro ; it gets into the cell and takes over everything.

A virus that contains RNA as its genetic material and that copies its genetic material from RNA to DNA

Retrovirus starts with R. A retrovirus copies its genetic material from RNA to DNA.

A nonliving particle made of proteins, nucleic acids, and sometimes lipids, that can only reproduce by infecting cells

Computer viruses can infect your computer.

Note: Students should highlight terms and definitions used throughout the chapter.

B. As you work through this lesson, you may find these terms in the activities. When you need to write a key term or a definition, highlight the term or the definition.

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The Discovery of Viruses

Viruses are particles made up of protein, genetic material, and sometimes lipids. The genetic material in a virus can be RNA or DNA. The protein coat that surrounds the genetic material is called the capsid.

Follow the directions.

1. Circle the genetic material in each virus.

2. Color the protein parts of each virus red.

T4 Bacteriophage

TToobbaacccocoMMosaoiscaViicruVs irus

Head

DNA

Influenza Virus (red)

Capsid

(red)

Capsid

(red)

(red)

Answer the questions. 1. Where is the genetic material in a T4 bacteriophage located? The genetic material is

located in the head.

2. In general, is the genetic material in a virus inside or outside the protein parts? inside

3. Why do you think the word virus, based on the Latin word for poison, was used for these

structures?

Sample answer: because many viruses cause disease

BUILD Understanding

Venn Diagram A Venn diagram is made up of overlapping circles. It is a useful tool for

comparing two or even three topics.

As you read Lesson 1, complete the Venn diagram below with information about viruses and cells.

Viruses

Cells

? nonliving

? cannot grow

Both

? does not obtain

? can reproduce

energy

? change over

? can only reproduce

time

in host cell

? have genetic

code

? living ? can grow ? can obtain energy ? can reproduce

independently

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Viral Infections

A bacteriophage is a virus that can infect bacteria. A lytic infection is one kind of viral infection. It results in lysis, or bursting of the host cell.

A lysogenic infection is another kind of viral infection. It occurs when viral DNA inserts itself into the DNA of the host cell. The viral DNA is replicated along with the host cell DNA. Eventually, the viral DNA separates from the host DNA. It then directs the construction of new virus particles.

The diagram below compares lytic and lysogenic infections.

Use the sentences to complete the diagram.

The proteins and nucleic acids assemble into new viruses. Viral genes are transcribed by the host cell. The virus injects DNA into a bacterium. The prophage may replicate with the bacterium for many generations.

The virus injects DNA into a bacterium.

Prophage

The viral DNA inserts itself into the bacterial chromosome, where it is called a prophage.

LYTIC INFECTION

LYSOGENIC INFECTION

The prophage may replicate with the bacterium for many generations.

Viral enzymes lyse the bacterium's cell wall. The new viruses escape and infect other bacterial cells.

Viral genes are transcribed by the host cell.

The proteins and nucleic acids assemble into new viruses.

The prophage can exit the bacterial chromosome and enter a lytic cycle.

The bacterium makes new viral proteins and nucleic acids.

Answer the questions. 1. Which type of viral infection includes the formation of a prophage? a lysogenic infection

2. What happens after viral enzymes lyse the bacterium's cell wall? The new viruses can

infect other bacterial cells.

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Viral Infections

Lytic Infections In a lytic infection, a virus enters a cell. It then copies itself and causes the

cell to burst. Lysing is another word for this type of cellular destruction. The flowchart below summarizes what happens in a lytic infection.

Follow the directions. 1. Use the following terms to complete the flowchart.

bacterium

viral proteins

virus

A virus enters or injects its DNA into a bacterium.

The bacterium then makes

viral proteins

and DNA.

New viruses are assembled and burst out of the

bacterium .

Answer the questions.

2. What is one result of a lytic infection? Circle the correct answer.

destruction of the virus

destruction of the host

3. What happens to the viruses after they lyse the cell wall?They infect other cells.

BUILD Connections

How a Lytic Virus Is Like an Outlaw An analogy compares two things that are

different and shows how they can be similar. 1. How does the analogy of the lytic virus to an outlaw help you understand lytic viruses?

Sample answer: It helps me understand that a lytic virus

breaks in and takes over the host cell's DNA. The virus then

uses the host cell to make viral DNA and viral proteins. The

host cell bursts, releasing hundreds of virus particles.

2. Find a partner. Using the analogy, explain how a lysogenic infection is also like an outlaw.

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