CHAPTER 19 NOTES

VIRUSES

CHARACTERISTICS OF VIRUSES

Prokaryotic or Eukaryotic: Neither (no organelles or membranes)

Unicellular or Multicellular: Neither (nucleic acid covered by a protein)

Autotroph or Heterotroph: Neither (food is not metabolized for energy)

Which Kingdom do they belong to? None

CHARACTERISTICS OF VIRUSES

2 MAIN PARTS OF A VIRUS:

1. PROTEIN COAT (CAPSID): PROTECTS THE NUCLEIC ACID CORE

2. CORE OF NUCLEIC ACID (CAN BE DNA OR RNA)

An envelope is found in some viruses (usually those that infect animal cells). It is an additional protective coating.

Many viruses have projections on their surface that allow it to enter a host cell.

EXAMPLE OF A BACTERIOPHAGE

VIRAL DNA

SHEATH

TAIL FIBERS

PROTEIN COAT (CAPSID)

HOW DO VIRUSES MULTIPLY?

Viruses perform replication in other cells called hosts.

The two replication cycles that viruses go through are the lytic and the lysogenic cycles.

The two cycles differ because in the lytic cycle a virus immediately replicates after entering the cell and in the lysogenic cycle the viral DNA replicates itself in a way that doesn’t kill the host cell immediately.

See next page for drawings of the cycles.

LYTIC CYCLE

LYSOGENIC CYCLE

HOW ARE VIRUSES CLASSIFIED?

VIRUSES CAN BE CLASSIFIED BY:

– A. SHAPE

– B. HOST

– C. FUNCTION

Examples of Different Types of Human Viruses

Influenza (Flu)

Examples of Different Types of Human Viruses

HIV

Examples of Different Types of Human Viruses

Smallpox & Hanta virus

Examples of Different Types of Human Viruses

Marburg & Lassa

Examples of Different Types of Human Viruses

Ebola

THREE TYPES OF HOSTS

A. PLANTEx. Tobacco Mosaic Virus

B. ANIMALEx. Rabies, Foot & Mouth Disease

C. HUMANEx. Common cold, measles, chicken pox,

mumps, HIV

TREATMENT OF VIRAL DISEASES

Viral diseases cannot be cured by antibiotics.

Generally with viral infections you are limited to relieving symptoms while your immune system battles the virus.

HUMAN USES FOR VIRUSES

1. VACCINES When you inject a person with a harmless –

weakened or dead form of a virus This stimulates the immune system to produce

cells and proteins that will destroy that type of virus, if it enters the body again

This helped to end epidemics of smallpox, polio and measles

HUMAN USES FOR VIRUSES

2. GENETIC ENGINEERING Viruses can help correct genetic defects by

carrying desirable genes from one cell to another

3. AGRICULTURE Help control pests that destroy human food

crops They eliminate harmful insects without creating

pollution

Virus Video Clips

http://ed.ted.com/lessons/how-pandemics-spread

http://www.youtube.com/watch?v=Rpj0emEGShQ

http://www.youtube.com/watch?v=gf2bObJGFkg