viruses section 19–2 section 19–2 this section describes the structure of a virus. it also...

Viruses Viruses

Section 19–2Section 19–2 This section describes the This section describes the

structure of a virus. It also structure of a virus. It also explains how viruses cause explains how viruses cause infection. infection.

What Is a Virus? What Is a Virus?

What are Viruses?What are Viruses?

They are particles of nucleic acid, They are particles of nucleic acid, protein, and in some cases lipids that protein, and in some cases lipids that can reproduce only by infecting living can reproduce only by infecting living cells. cells.

What do all viruses have in What do all viruses have in common?common?

They enter living cells and, once inside, They enter living cells and, once inside, use the machinery of the infected cell to use the machinery of the infected cell to produce more viruses. produce more viruses.

Is the following sentence true Is the following sentence true or false? or false?

Most viruses are so small that they Most viruses are so small that they can be seen only with the aid of a can be seen only with the aid of a powerful electron microscope.powerful electron microscope.

TrueTrue

What Is a Virus?What Is a Virus?

What is the structure of a typical What is the structure of a typical virus?virus?

A typical virus is composed of a core A typical virus is composed of a core of either DNA or RNA surrounded by of either DNA or RNA surrounded by a protein coat. a protein coat.


Circle the letter of what a Circle the letter of what a virus’s protein coat is called.virus’s protein coat is called.

capsidcapsid


How does a typical virus get inside a How does a typical virus get inside a cell?cell?

The capsid proteins bind to receptors The capsid proteins bind to receptors on the surface of a cell and “trick” on the surface of a cell and “trick” the cell into allowing it inside. the cell into allowing it inside.


What occurs when viruses get inside What occurs when viruses get inside of cells? of cells?

Once inside, the viral genes are Once inside, the viral genes are expressed. The cell transcribes and expressed. The cell transcribes and translates the viral genetic information translates the viral genetic information into viral capsid proteins. Sometimes the into viral capsid proteins. Sometimes the program may cause the cell to make program may cause the cell to make copies of the virus, and in the process the copies of the virus, and in the process the host cell host cell is destroyed.is destroyed.


Why are most viruses highly Why are most viruses highly specific to the cells they infect? specific to the cells they infect?


Viruses must bind precisely to Viruses must bind precisely to proteins on the cell surface and proteins on the cell surface and then use a host’s genetic then use a host’s genetic system.system.


What are bacteriophages?What are bacteriophages?

They are viruses that infect They are viruses that infect bacteria. bacteria. Viral Infection Viral Infection


Why is a lytic infection given Why is a lytic infection given that name? that name?

The host cell is lysed and The host cell is lysed and destroyed.destroyed.


Circle the letter of each sentence Circle the letter of each sentence that is true about a lysogenic that is true about a lysogenic infection. infection.

The virus embeds its DNA into The virus embeds its DNA into the host’s DNA. the host’s DNA.


The virus’s DNA is replicated The virus’s DNA is replicated along with the host cell’s DNA. along with the host cell’s DNA.

A host cell makes copies of the A host cell makes copies of the virus indefinitely. virus indefinitely.

Complete the flowchart Complete the flowchart about a lytic infection. about a lytic infection.


What is prophage?What is prophage?

It is the viral DNA that is embedded It is the viral DNA that is embedded in the host’s DNA. in the host’s DNA.


RetrovirusesRetroviruses What are retroviruses?What are retroviruses?

They are viruses that contain RNA as They are viruses that contain RNA as their genetic information. their genetic information.


What happens when retroviruses What happens when retroviruses infect a cell? infect a cell?

They produce DNA copy of their RNA. This DNA is They produce DNA copy of their RNA. This DNA is inserted into the DNA of the host cell. inserted into the DNA of the host cell.


Viruses and Living Cells Viruses and Living Cells Circle the letter of each reason Circle the letter of each reason

why some biologists do not why some biologists do not consider viruses to be alive. consider viruses to be alive.

They can’t reproduce They can’t reproduce independently. independently.

viruses section 19–2 section 19–2 this section describes the structure of a virus. it also...

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