Ch 18 Viruses and Bacteria by ert554898


									 Ch 18 Viruses and Bacteria
 04 Biology 2008

 From Mrs. C. Phillips, DHS

Ch 18.1 Viruses
•   What kinds of diseases are caused by viruses?
•   Measles
•   Mumps
•   Rubella
•   Chicken pox
•   Polio
•   Cold sores
•   Herpes
•   Rabies
•   Flu
•   Cold
•   HIV
•   Viral pneumonia
•   Hepatitis
•   Mono (if caused by Epstein-Barr virus)
What kingdom do viruses belong
• None- they are not alive!!
• They are nonliving particles that
  cause disease
• pathogens: agents that cause disease
• Characteristics:
   – 1/2 -1/100 the size of the smallest
   – Do not grow, respire, metabolize,
     develop, respire, maintain
   – Do not have scientific names (named
     for the disease or tissue they infect)
       • Ex: adenovirus (cold virus) infects
         adenoid tissue
                                                 Viral Structure 1

      Viral Structure            • A virus has an inner
                                   core of nucleic
                                   acid, either RNA or
                                   DNA, and an outer
                       Nucleic     protein coat called
                                   a capsid.


• Some relatively large viruses may have an
  additional layer, called an envelope,
  surrounding their capsids.
                        • The arrangement of
Capsid                    proteins in the capsid
         Nucleic acid
                          of a virus determines
                          the virus’s shape.
                        • Polyhedral viruses
                          resemble small
Nucleic acid   • The tobacco mosaic virus
                 has a long, narrow helical

Replication of Viruses
• There are two ways in
  which a virus can
  1. Lytic Cycle and
  2. Lysogenic Cycle

Each cycle first involves
  attachment to the host
• A virus recognizes and
  attaches to a host cell
  when one of its proteins
  interlocks with a molecular
  shape that is the receptor
  site on the host cell’s
  plasma membrane.
• Viruses are specific to only
  certain types of cells.
Host specificity

                    • The T4 bacteriophage
      Nucleic         can only infect E. Coli
      acid            cells.
                    • HIV can only infect
      Tail            certain white blood
       Tail fiber
                    • Polio can only infect
                      intestinal and nerve
Lytic Cycle
                  Bacteriophage           Bacterial DNA

    host cell
                                                   B. Entry
                         A. Attachment
                                                   The bacteriophage
                                                   injects its nucleic acid
                                                   into the bacterial cell.

                              E. Lysis and Release
                              The host cell breaks open and
                              releases new virus particles.

                                                                       C. Replication
        D. Assembly
                                                                        The host’s metabolic
        New virus particles                                             machinery makes viral
        are assembled.                                                  nucleic acid and proteins.

                                                                                        Lytic Cycle
Lysogenic Cycle
                              B. Provirus Formation
     A. Attachment and Entry
                                                                                            the provirus
                                                                                            is inactive,
                 Bacterial host
                                                                C. Cell Division            it replicates
                                                                                            along with
                                                                                            the host cell’s
   A lysogenic virus
                                  The viral nucleic acid is called
   injects its nucleic            a provirus when it becomes
   acid into a bacterium.         part of the host’s chromosome.

                            LYSOGENIC CYCLE
                                    LYTIC CYCLE                       The provirus leaves
                                                                      the chromosome.
                       The cell breaks
                       open releasing
                       viruses.              Viral nucleic acid and
                                             proteins are made.

                                                                                                 Lysogenic Cycle
    Release of Viruses
• Either lysis, the bursting of a cell, or exocytosis,
  the active transport process by which materials
  are expelled from a cell, release new viruses
  from the host cell.
• Have RNA as their nucleic
• Once inside cell, the RNA is
  turned into DNA by a
  process called reverse

               HIV virus
Reverse Transciption
• This requires the enzyme
  reverse transcriptase which
  is carried along in the virus.
• Then the viral DNA
  becomes part of the host’s
  DNA as a provirus.
 Retrovirus Cycle
    Retrovirus                    RNA          DNA is made from
                        RNA                    the viral RNA.

transcriptase      Entering

                                        Provirus in
                                        host chromosome


Retrovirus Cycle

                                                       New virus parts

                        Exiting    New virus
                        cell       forming
Question 1
Which of the following is NOT a reason that
viruses are considered to be nonliving?

A.   Viruses don’t replicate.
B.   Viruses don’t respire.
C.   Viruses don’t grow.
D.   Viruses don’t develop.
The answer is A.
Question 2
Which is NOT a component of a virus?

B. capsid
D. phage
The answer is D.
Question 3
Which of the following is NOT determined by the
arrangement of proteins in the capsid of a virus?

A. shape
B. what cell can be infected by the virus
C. whether or not the virus will have an
   envelope around it
D. how the virus infects a cell
     The answer is C.
Question 4
What two ways do viruses have of getting into host

The virus can inject its nucleic acid into the host
cell, or attach to the host cell’s membrane and
become surrounded by the membrane and
placed in a vacuole. The virus then bursts out of
the vacuole and releases its nucleic acid into the
Question 5
In the lytic cycle, after the host’s metabolic
machinery makes viral nucleic acid and proteins
the next phase is _______.

A. lysis and release
B. replication
C. assembly
D. attachment
The answer is C. In the assembly phase, the new virus
particles are assembled.
Ch 18.2 Bacteria
•   Bacteria
•   Bacteria Importance
•   Bacteria Diseases
•   Bacterial Reproduction
Question 6
Which of the following is not a way to
identify bacteria?

 A. the way in which their cell walls
    reflect Gram stain
 B. shape
 C. characteristic growth patterns
 D. lack of a plasma membrane
 The answer is D.
Question 7
Given their rapid reproductive rates, why aren’t there
more bacteria than there actually are?

Bacteria don’t always have ideal growing
conditions. They run out of nutrients and water,
they poison themselves with their own wastes,
and predators eat them.
Question 8
What is a pilus used for in a bacterium?
A pilus helps a bacterium stick to a surface.
It is also a bridge through or on which two
bacteria can exchange DNA.
         Capsule     Cell Wall

         Plasma                        Flagellum
                    Pilus        Plasmid
Question 9
With lysogenic viruses, what two phases of the
lytic cycle are replaced by the lysogenic cycle?

A. entry and replication
B. replication and assemble
C. assembly and lysis and release
D. attachment and entry
The answer is D.
         A. Attachment and Entry

                           LYSOGENIC CYCLE

                               LYTIC CYCLE
Question 10
Explain why you can be infected with a virus
but may have no symptoms of disease for
years after the initial infection.
The virus enters a lysogenic phase remaining
inactive but replicating along with the host
cell’s chromosomes. Eventually, the virus
enters a lytic phase where it destroys its host
cells and causes symptoms of disease.
Question 11
What is the difference between lysis and
exocytosis with respect to host cells that
contain viruses?
Lysis, the bursting of the host cell, is caused
when viruses break out of it. In exocytosis, the
virus is enclosed in a vacuole that then fuses
with the host cell’s plasma membrane. The
virus is then released to the outside.
Question 12
What is the importance of reverse
transcriptase to a retrovirus?

The enzyme reverse transcriptase allows the
retrovirus to make DNA from its RNA so the
DNA may attach to the chromosomes of the
host cell and divide with the host cell.
Question 13
Particles that are composed of proteins but have
no nucleic acid to carry genetic information are
A.   proviruses
B.   prions
C.   viroids
D.   retroviruses
 The answer is B.
Question 14
During ______, a bacterium transfers all or part
of its chromosome to another bacterium.
A.   binary fission
B.   attachment
C.   conjugation
D.   chemosynthesis

The answer is C.
Question 15
What causes botulism?

Endospores of C. botulinum bacteria get into
an anaerobic environment like improperly
canned food, germinate, and produce a toxin
as they grow. This toxin is then ingested by
humans and causes poisoning called
Question 16
What causes anthrax?
Endospores of B. anthracis bacteria produce
endospores that can become airborne, and if
inhaled in large amounts, can germinate in a
person’s lungs causing a deadly infection that
damages lung tissue and the circulatory
Question 17
Describe the process in which bacteria make
nitrogen in the air accessible for use by plants.
Several species of bacteria have enzymes that
convert nitrogen gas into ammonia. Other
bacteria then convert the ammonia into nitrite
and nitrate that plants can use.
Question 18
What are the two ways in which bacterial
diseases harm people?

The growth of the bacteria can interfere with
the normal function of body tissue, or the
bacteria can release a toxin that directly
attacks the host.

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