Viruses and Prokaryotes What Viruses Mean To You If you have ever had a cold, you are probably...

Viruses and Prokaryotes

What Viruses Mean To You

• If you have ever had a cold, you are probably familiar with the word virus. It is a word that makes most people frown.

Section 19-3

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1. What do you think of when you hear the word virus? Make a list of all the words you can think of that relate to viruses.

2. What are two things that you would like to find out about viruses?


VirusesA. What Is a Virus?

B. Viral Infection

1. Lytic Infection

2. Lysogenic Infection

C. Viruses and Disease

1. Viruses and Cancer

2. Retroviruses

3. Prions

D. Are Viruses Alive?

Section 19-3

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KEY CONCEPT Infections can be caused in several ways.


Section 19-3Common Diseases Caused by Viruses

Oncogenic viruses

Retroviruses

Adenoviruses

Herpesviruses

Poxviruses

DNA

RNA

DNA

DNA

DNA

cancer

cancer, AIDS

respiratory infections

chickenpox

smallpox

Type of Virus Nucleic Acid Disease

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Viruses, bacteria, viroids, and prions can all cause infection.

• Any disease-causing agent is called a pathogen.

viruses50-200 nm

prokaryotics cells200-10,000 nm

prion2-10 nm

viroids5-150 nm

eukaryotics cells10,000-100,000 nm

100 nm

1 nanometer (nm) = one billionth of a meter


What are Viruses

A virus is a non-cellular particle made up of genetic material and protein that can invade

living cells.


The Structure Of a Virus (Draw the shown diagram)

• Viruses are composed of a core of nucleic acid

• The Nucleic acid core is surrounded by a protein coat called a capsid

• The Nucleic core is either made up of DNA or RNA but never both


• A virus is made of DNA or RNA and a protein coat.

– non-living pathogen – can infect many

organisms • A viroid is made only

of single-stranded RNA. – causes disease in

plants– passed through

seeds or pollen


• A prion is made only of proteins.

– causes misfolding of other proteins – results in diseases of the brain


KEY CONCEPT Viruses exist in a variety of shapes and sizes.


Viruses differ in shape and in ways of entering host cells. • Viruses have a simple structure.

– genetic material – capsid, a protein shell – maybe a lipid envelope, a protective outer coat

capsid nucleic acid

lipidenvelope

surfaceproteins

capsid

nucleic acid

lipid envelope

Surface proteins capsidsurfaceproteins

nucleic acid

helical(rabies)

polyhedral(foot-and-mouth

disease)

enveloped(influenza)


T4 BacteriophageTobacco Mosaic

Virus Influenza Virus

Head

Tail sheath

DNA

Tail fiber

RNACapsid

Surfaceproteins Membrane

envelope

RNA

Capsidproteins

Section 19-3Figure 19-13 Virus Structures

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• Viruses enter cells in various ways.

colored SEM; magnifications:large photo 25,000; inset 38,000x

– bacteriophages pierce host cells


T4 Bacteriophage


Herpes Virus

13.1 Ecologists Study RelationshipsEscherichia Coli Bacterium

E. coli is a bacterium. That is a crude cell, it is not a virus because viruses are protein containers with DNA cores or

RNA cores.

13.1 Ecologists Study Relationships

E. Coli and the Bacteriophage

What it looks like in real life


– viruses of eukaryotes enter by endocytosis



– viruses of eukaryotes also fuse with membrane



host bacterium

The bacterophage attachesand injects it DNA into a host bacterium.

The host bacterium breaks apart, or lyses. Bacteriophages are ableto infect new host cells.

The viral DNA directs the hostcell to produce new viral parts.The parts assemble into newbacteriophages.

The viral DNA forms a circle.

Viruses cause two types of infections.

• A lytic infection causes the host cell to burst.

The virus may enter thelysogenic cycle, in which thehost cell is not destroyed.


• A lysogenic infection does no immediate harm.

The viral DNA is called a prophagewhen it combines withthe host cell’s DNA.

Although the prophage is notactive, it replicates along withthe host cell’s DNA.

Many cell divisions produce acolony of bacteria infectedwith prophage.

The prophage may leave thehost’s DNA and enter thelytic cycle.


KEY CONCEPT Some viral diseases can be prevented with vaccines.


Viruses cause many infectious diseases

• There are many examples of viral infections.– common cold


– influenza




– influenza



– SARS


– HIV

HIV-infected whiteblood cell


• There are many examples of viral infections.

• The body has natural defenses against viruses.


Retrovirus

• Change DNA into RNA.

• Example of a Retrovirus is HIV

Viruses and ProkaryotesA typical, "minimal" retrovirus consists of: •an outer envelope which was derived from the plasma membrane of its host •many copies of an envelope protein embedded in the lipid bilayer of its envelope •a capsid; a protein shell containing •two molecules of RNA and •molecules of the enzyme reverse transcriptase


Vaccines

• Viruses grown on chicken embryos are attenuated vaccines

• Another type of vaccine is made by heat killing the virus


Vaccines are made from weakened pathogens.

• A vaccine stimulates the body’s own immune response. • Vaccines prepare the immune system for a future attack.

• Vaccines are the only way to control the spread of viral disease.

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