Transcript Chapter 24 Viruses Table of Contents Section 1 Viral Structure and Replication Section 2 Viral Diseases.

Chapter 24
Viruses
Table of Contents
Section 1 Viral Structure and Replication
Section 2 Viral Diseases
Chapter 24
Section 1 Viral Structure and
Replication
Objectives
• Summarize the discovery of viruses.
• Describe why viruses are not considered living
organisms.
• Describe the basic structure of viruses.
• Compare the lytic and lysogenic cycles of virus
replication.
• Summarize the origin of viruses.
Chapter 24
Section 1 Viral Structure and
Replication
Discovery of Viruses
• Researchers in the late 1800s discovered that
something smaller than bacteria could cause
disease.
• In 1935, Wendell Stanley demonstrated that viruses
were not cells when he crystallized TMV, the virus
that causes tobacco mosaic disease in tobacco and
tomato plants.
Chapter 24
Section 1 Viral Structure and
Replication
Virus
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Visual Concept
Chapter 24
Section 1 Viral Structure and
Replication
Characteristics of Viruses
• Viruses do not have all of the characteristics of life
and are therefore not considered to be living.
Chapter 24
Section 1 Viral Structure and
Replication
Characteristics of Viruses, continued
• Viral Size and Structure
– Viruses are nonliving particles containing DNA or
RNA and are surrounded by a protein coat called
a capsid.
– Some viruses also have an envelope that is
derived from a host cell’s nuclear membrane or
cell membrane.
Chapter 24
Section 1 Viral Structure and
Replication
Parts of a Virus
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Visual Concept
Chapter 24
Section 1 Viral Structure and
Replication
Characteristics of Viruses, continued
• Classification of Viruses
– Viruses can be classified based on whether they
have RNA or DNA, whether the RNA or DNA is
single or double stranded and circular or linear, by
capsid shape, and whether or not they have an
envelope.
Chapter 24
Section 1 Viral Structure and
Replication
Viral Replication, continued
• Replication in DNA Viruses
– DNA viruses can enter host cells and directly
produce RNA, or they can insert into a host’s
chromosome, where they are transcribed to RNA
along with the host’s DNA.
Chapter 24
Section 1 Viral Structure and
Replication
Viral Replication, continued
• Replication in RNA Viruses
– The RNA genome of some RNA viruses can be
directly translated to make viral proteins.
– Retroviruses use reverse transcriptase and
RNA as a template to make DNA, which is then
used to produce viral RNA and proteins.
Chapter 24
Section 1 Viral Structure and
Replication
Viral Replication, continued
• Replication in Viruses That Infect Prokaryotes
– Bacteriophages are viruses that infect bacteria.
Chapter 24
Section 1 Viral Structure and
Replication
Viral Replication, continued
• Lytic Cycle
– Viruses can follow a lytic cycle, making new viral
particles immediately.
Chapter 24
Section 1 Viral Structure and
Replication
Lytic Cycle
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Visual Concept
Chapter 24
Section 1 Viral Structure and
Replication
Viral Replication, continued
• Lysogenic Cycle
– Viruses can follow a lysogenic cycle, becoming
part of the host genome and making new particles
later.
Section 1 Viral Structure and
Replication
Chapter 24
Lysogenic Cycle
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Visual Concept
Chapter 24
The Lytic and
Lysogenic
Cycles
Section 1 Viral Structure and
Replication
Chapter 24
Section 1 Viral Structure and
Replication
Viral Replication, continued
• Viruses: Tools for Biotechnology
– Viruses are important tools for biotechnology.
Chapter 24
Section 1 Viral Structure and
Replication
The Origin of Viruses
• Most scientists think viruses originated from
fragments of host-cell nucleic-acid material.
Chapter 24
Section 2 Viral Diseases
Objectives
• Name several vectors of viral diseases.
• Identify four viral diseases that result in serious human
illnesses.
• Discuss the relationship between viruses and cancer.
• Name three examples of emerging viral diseases.
• Compare the effectiveness of vaccination, vector control, and
drug therapy in fighting viruses.
• Contrast viroids, prions, and viruses.
Chapter 24
Section 2 Viral Diseases
Vectors of Viral Diseases
• Vectors, or hosts, of viral diseases include humans,
animals, and insects.
Chapter 24
Section 2 Viral Diseases
Human Viral Diseases
• Viruses cause many human diseases, including the
common cold, flu, hepatitis, rabies, chickenpox,
certain types of cancer, and AIDS.
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Section 2 Viral Diseases
Human Viral Diseases, continued
• Chickenpox and Shingles
– Chickenpox and shingles are caused by the same
varicella-zoster herpesvirus.
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Section 2 Viral Diseases
Human Viral Diseases, continued
• Viral Hepatitis
– Hepatitis, or inflammation of the liver, can be
caused by at least five viruses.
– Hepatitis A and hepatitis E can be spread by
fecally contaminated food and water.
– Hepatitis B, C, and D are spread by sexual
contact, by contact with infected blood and
serum,and by the use of contaminated needles.
Chapter 24
Section 2 Viral Diseases
Human Viral Diseases, continued
• Acquired Immune Deficiency Syndrome (AIDS)
– The human immunodeficiency virus (HIV) is an
RNA virus spread by sexual contact, by contact
with infected body fluids, and from mother to fetus.
– HIV targets macrophages and thus damages the
body’s immune system. The disease called
acquired immune deficiency syndrome (AIDS)
results.
Chapter 24
Section 2 Viral Diseases
AIDS (Acquired Immunodeficiency Syndrome)
Chapter 24
Section 2 Viral Diseases
Human Viral Diseases, continued
• Viruses and Cancer
– Some viruses contain oncogenes that can cause
cancer, while other viruses convert protooncogenes, which usually control cell growth, to
oncogenes.
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Section 2 Viral Diseases
Emerging Viral Diseases
• Emerging viruses usually infect animals isolated in
nature but can jump to humans when contact occurs
in the environment.
Chapter 24
Section 2 Viral Diseases
Prevention and Treatment
• Vaccinations
– A vaccine contains a harmless version of a virus,
bacterium, or a toxin that causes an immune
response when introduced to the body.
– Vaccines have helped to greatly reduce certain
viral diseases.
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Section 2 Viral Diseases
Prevention and Treatment, continued
• Vector Control
– Control efforts, including killing mosquitoes and
other vectors and quarantining ill patients, have
helped reduce the spread of certain viral diseases.
Chapter 24
Section 2 Viral Diseases
Prevention and Treatment, continued
• Drug Therapy
– Antibiotics are ineffective against viral diseases.
– Viral drugs, such as acyclovir, block specific steps
in viral replication.
Chapter 24
Section 2 Viral Diseases
Virods and Prions
• Viroids are short, circular, single strands of RNA
lacking a capsid that infect plant cells.
• Prions are infectious particles containing protein but
no nucleic acids.
– Prions cause mad cow disease and similar
degenerative brain diseases.
Chapter 24
Important
Viral
Diseases
Section 2 Viral Diseases