Ch 18 Viruses and Bacteria
04 Biology 2008
From Mrs. C. Phillips, DHS
black
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
to?
• 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
bacteria
– Do not grow, respire, metabolize,
develop, respire, maintain
homeostasis
– 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
Capsid
Nucleic
acid
• A virus has an inner
core of nucleic
acid, either RNA or
DNA, and an outer
protein coat called
a capsid.
Envelope
• Some relatively large viruses may have an
additional layer, called an envelope,
surrounding their capsids.
Capsid
Nucleic acid
• The arrangement of
proteins in the capsid
of a virus determines
the virus’s shape.
• Polyhedral viruses
resemble small
crystals.
Nucleic acid
• The tobacco mosaic virus
has a long, narrow helical
shape.
Capsid
Replication of Viruses
• There are two ways in
which a virus can
repilcate:
1. Lytic Cycle and
2. Lysogenic Cycle
Each cycle first involves
attachment to the host
cell.
Attachment
• 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
Capsid
Nucleic
acid
Tail
Tail fiber
• The T4 bacteriophage
can only infect E. Coli
cells.
• HIV can only infect
certain white blood
cells.
• Polio can only infect
intestinal and nerve
cells.
Lytic Cycle
Bacteriophage
Bacterial DNA
Nucleic
acid
Bacterial
host cell
A. Attachment
B. Entry
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
New virus particles
are assembled.
The host’s metabolic
machinery makes viral
nucleic acid and proteins.
Lytic Cycle
Lysogenic Cycle
B. Provirus Formation
A. Attachment and Entry
Provirus
C. Cell Division
Bacterial host
chromosome
A lysogenic virus
injects its nucleic
acid into a bacterium.
Although
the provirus
is inactive,
it replicates
along with
the host cell’s
chromosome.
The viral nucleic acid is called
a provirus when it becomes
part of the host’s chromosome.
LYSOGENIC CYCLE
LYTIC CYCLE
The cell breaks
open releasing
viruses.
The provirus leaves
the chromosome.
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.
Retroviruses
• Have RNA as their nucleic
acid
• Once inside cell, the RNA is
turned into DNA by a
process called reverse
transcription
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
RNA
Retrovirus
DNA is made from
the viral RNA.
RNA
DNA
Reverse
transcriptase
Entering
cell
Provirus in
host chromosome
mRNA
Retrovirus Cycle
New virus parts
Exiting
cell
New virus
forming
Question 1
Which of the following is NOT a reason that
viruses are considered to be nonliving?
A.
B.
C.
D.
Viruses don’t replicate.
Viruses don’t respire.
Viruses don’t grow.
Viruses don’t develop.
The answer is A.
Question 2
Which is NOT a component of a virus?
A. RNA
B. capsid
C. DNA
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
cells?
Answer
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
cell.
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?
Answer
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
Chromosome
Plasma
membrane
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.
Answer
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?
Answer
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?
Answer
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.
B.
C.
D.
proviruses
prions
viroids
retroviruses
The answer is B.
Question 14
During ______, a bacterium transfers all or part
of its chromosome to another bacterium.
A.
B.
C.
D.
binary fission
attachment
conjugation
chemosynthesis
The answer is C.
Question 15
What causes botulism?
Answer
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
botulism.
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
system.
Question 17
Describe the process in which bacteria make
nitrogen in the air accessible for use by plants.
Answer
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?
Answer
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.