Lesson 3 Reading Guide

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Lesson 3 Reading Guide
Lesson 7-3 What are Viruses?
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Lesson 3
Characteristics of Viruses

• A virus is a strand of DNA surrounded by a layer
  of protein that can infect and replicate in a
  host cell.

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Lesson 3
Characteristics of Viruses (cont.)

• A virus
• is smaller than the smallest bacteria!
• http//learn.genetics.utah.edu/content/begin/cells
  /scale/
• Viruses contain proteins, nucleic acids can
  reproduce
• But..

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Virus characteristics
Characteristics of Viruses (cont.)

• Viruses
• Dont eat, grow or breathe
• Do not have any organelles, or a cell membrane.
• They are NOT cells!
• Based on this info, do you think viruses are
  living organisms????
• No!
• A virus is not a living thing because it does not
  have all the characteristics of a living organism.

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Lesson 3
Characteristics of Viruses (cont.)

• Viruses can have different shapes, such as
  crystal, cylinder, sphere, and bacteriophage
  shapes.

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Bacteriophage virus
Characteristics of Viruses (cont.)

• Bacteriophage viruses only infect bacteria

Protein coat
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Lesson 3
Characteristics of Viruses (cont.)

• Viruses must use organisms to carry on the
  processes that we usually associate with a living
  cell.
• Viruses must be inside a cell, called a host
  cell, to replicate.

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Lesson 3
Characteristics of Viruses (cont.)

• When a virus enters a cell, it can either be
  active or latent.
• Latent viruses go through an inactive stage and
  their genetic material becomes part of the host
  cells genetic material.
• Once it becomes active, a virus takes control of
  the host cell and replicates.

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Viral reproduction
Lytic Cycle

• Even though viruses are not truly a living
  organism, they can reproduce.
• How?
• The Lytic Cycle
• A 4-step process
• http//www.youtube.com/watch?vwVkCyU5aeeU

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Lytic Cycle
Step 2 - injection
Step 1- attachment
Step 3- Replication
Step 4 - Escape
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Lytic Cycle
Lytic Cycle

1. Virus attaches to a host cell
2. Virus injects DNA into the host cell
3. Host cell is then directed to make more viral
   DNA, and new protein coats (replication)
4. The host cell is often destroyed and the viruses
   escape and move on to infect other cells

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Lesson 3
Characteristics of Viruses (cont.)

• As viruses replicate, their DNA or RNA frequently
  mutates, enabling them to adjust to changes in
  their host cell.
• Viruses cause many human diseases, such as
  chicken pox, influenza, HIV, and the common cold.
  Viruses can also affect other animals and plants.

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Lesson 3
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Lesson 3
Treating and Preventing Viral Diseases

• Since viruses are constantly changing, viral
  diseases can be difficult to treat.
• Antibiotics work only against bacteria, not
  viruses.
• One of the best ways to prevent a viral infection
  is to limit contact with an infected human or
  animal.

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Lesson 3
Treating and Preventing Viral Diseases(cont.)

• When a virus infects a person, their body begins
  to make antibodies.
• An antibody is a protein that prevents an
  infection in your body.
• Antibodies bind to viruses and other pathogens
  and prevent them from attaching to a host cell.

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Lesson 3
Treating and Preventing Viral Diseases(cont.)

• Natural immunity develops when a mother passes
  antibodies on to her unborn baby.

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Lesson 3
Treating and Preventing Viral Diseases(cont.)

• A vaccine is a mixture containing material from
  one or more deactivated pathogens, such as
  viruses.
• When an organism is given a vaccine for a viral
  disease, the vaccine triggers the production of
  antibodies.
• After being vaccinated against a particular
  pathogen, the organism will not get as sick if
  exposed to the same pathogen again.

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Lesson 3
Research with Viruses

• Scientists are researching new ways to treat and
  prevent viral diseases in humans, animals, and
  plants.
• Viruses have been used by some scientists to
  treat genetic disorders and cancer using gene
  transfer.