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Lesson 3 Reading Guide

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Lesson 7-3 What are Viruses? Lesson 3 Reading Guide Lesson 3 A virus is a strand of DNA surrounded by a layer of protein that can infect and replicate in a host cell. – PowerPoint PPT presentation

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Title: Lesson 3 Reading Guide


1
Lesson 3 Reading Guide
Lesson 7-3 What are Viruses?
2
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.

3
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..

4
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.

5
Lesson 3
Characteristics of Viruses (cont.)
  • Viruses can have different shapes, such as
    crystal, cylinder, sphere, and bacteriophage
    shapes.

6
Bacteriophage virus
Characteristics of Viruses (cont.)
  • Bacteriophage viruses only infect bacteria

Protein coat
7
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.

8
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.

9
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

10
Lytic Cycle
Step 2 - injection
Step 1- attachment
Step 3- Replication
Step 4 - Escape
11
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

12
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.

13
Lesson 3
14
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.

15
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.

16
Lesson 3
Treating and Preventing Viral Diseases(cont.)
  • Natural immunity develops when a mother passes
    antibodies on to her unborn baby.

17
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.

18
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.
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