Download Characteristics of Viruses-Parts 1_2_3

Student Name _________________________
Date _______________________________
Characteristics of Viruses--Part I
Level High School - Science
Prompt: This passage is called Characteristics
of Viruses. It is about viruses.
Similarities and Differences
Between Viruses and Cells
If you ever had a cold or the flu, you
probably hosted viruses. A virus is an
infectious agent made up of a core of nucleic
acid and a protein coat. Viruses are not cells.
Unlike plant and animal cells, a virus package
does not have a nucleus, a membrane, or
cellular organelles such as ribosomes,
mitochondria, or chloroplasts. Although
viruses are not cells, they do have organized
structural parts.
Compared to even the smallest cell, a
virus is tiny. The virus that causes polio, for
example, measures only 20 nanometers in
diameter. One nanometer is one billionth of a
meter. At that size, 3000 polioviruses could
line up across the period at the end of this
sentence.
All viruses have at least two parts: a
protective protein coat and a core of nucleic
acid. The protein coat around the core of the
nucleic acid is called a capsid. Depending on
the virus, the capsid may consist of one or
several kinds of protein. The capsid protects
the viral nucleic acid core from its
In cells, DNA is the hereditary material. Some
viruses also contain DNA, while other viruses
contain only RNA. In viruses containing
RNA, the RNA functions as the hereditary
material.
Compared to a cell, a virus has a
relatively simple existence. Viruses do not
eat, respire, or respond to environmental
changes as cells do. It should not surprise you,
therefore, to learn that viruses have fewer
genes than cells have. While a human cell
may contain about 100,000 genes and a
bacterial cell about 1000, a virus may contain
only 5 genes.
In the figure on the previous page, you
can see parts of an influenza virus: a core of
RNA, a surrounding capsid, and an outer
covering called an envelope. An envelope is
an additional protective coating usually made
up of lipids, proteins, and carbohydrates.
Envelopes are found only in viruses that infect
animal cells. An envelope has spike-like
projections that recognize and bind to
complementary sites on the membrane of the
cell being infected. Think about how a prickly
burr sticks to objects.
environment.
Division of Learning Services
Fall 2007
COMPREHENSION:
Characteristics of Viruses--Part I - Level High School - Science
1.
What is this section mainly about?
Implicit: it describes what a virus is and how it is different from a cell.
2.
What are the two parts of a virus?
Explicit: a core of acid (nucleic not required) and a protein (or protective) coat.
3.
What is the function of the protein coat of the virus?
Explicit: it protects the core of acid.
4.
Why isn't a virus a cell?
Implicit: it doesn't have a nucleus or a membrane or organelles. (Ribosomes, mitochondria,
and chloroplasts are not required.)
5.
If a virus contains both DNA and RNA, which functions as the hereditary material?
Explicit: RNA
6.
What determines the proteins in a capsid?
Explicit from figure: genes in the virus.
7.
How is the envelope of the influenza virus different from the capsid?
Implicit: it is an additional protective coating outside of the virus.
8.
What types of viruses have envelopes?
Explicit: viruses that infect animal cells.
9.
How does the envelope of the virus help the virus infect a cell?
Implicit: its projections bind to complementary sites on the cell membrane.
10.
How does the text suggest that the existence of a virus is less complex than that of a cell?
Implicit: viruses have fewer genes or their genetic makeup is less complex or they don't do as
many things as cells do. (That they don't respire or eat is correct but not required.)
Number Correct Explicit: ______
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Number Correct Implicit: ______
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Independent: 9-10 correct
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Instructional: 7-8 correct
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Frustration: 6 or less correct
Fall 2007
Student Name _________________________
Characteristics of Viruses--Part II
Level High School - Science
Date ________________________________
Prompt: This passage is called Characteristics
of Viruses. It is about viruses.
I am going to demonstrate a process
called think-aloud. When you are reading and
come to the word STOP in the text, I will ask
materials that viruses need to copy themselves.
STOP. So the viruses feed off the host sort of
like a parasite. (Making new meaning)
you to tell me what you are thinking about.
Then I will tell you what I am thinking about.
The purpose for this is to show you many
different kinds of thinking that can go on
during reading. At the end of the section, I
will ask you to retell what you remember, and
then I will ask you questions. When you read
the final section of text, I will ask you to do a
think-aloud alone while reading.
When it enters a host cell, a virus may
immediately begin to replicate, or it may
remain relatively inactive.
STOP.
probably have a lot of those inactive viruses in
our body and don't know about them. (Making
new meaning) The viral replication process
that rapidly kills a host cell is called the lytic
cycle. You can follow the lytic cycle in the
figure below. STOP. I am getting confused.
I hope the figure helps me.
Viral Replication:
Ticking Time Bobs
Viruses
do
not
reproduce,
(Questioning)
they
Reproduction,
which is characteristic of living things,
involves cell division. Replication does not
involve cell division.
answered
my
STOP.
question.
Well, they
(Noting
understanding). Viruses cannot replicate on
virus invades a host cell and begins to replicate
immediately, producing many new viruses.
STOP. The virus gets into a cell and begins to
replicate.
a host. STOP. I remember learning about a
host in science. (Reporting prior knowledge)
A host is an organism that shelters and
Living cells host
viruses. These host cells provide all the
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(Summarizing or paraphrasing)
Eventually, the host cell lyses, or breaks apart,
releasing the newly made viruses. The new
viruses may then enter other cells and repeat
the cycle.
As a child you may have had chicken
their own. In order to replicate, viruses require
nourishes something.
(Noting
understanding) The lytic cycle begins when a
replicate. STOP. I'm wondering what is the
difference?
We
pox, which is caused by a virus. while you
were ill, most of the viruses were in the lytic
cycle.
Because your cells were being
destroyed by the chicken pox virus, you
showed symptoms of the disease.
Fall 2007
(page 2: Characteristics of Viruses--Part II)
A host cell carrying a prophage may divide
STOP. I remember when I had the chicken
many times. The prophage is replicated every
pox. I was miserable (Identifying personally).
time the host cell's chromosome replicates.
Sometimes a virus does not start the
lytic cycle immediately.
Instead the virus
enters the lysogenic cycle.
STOP. I get the idea of the prophage (Noting
understanding)
The lysogenic
Some
prophages
remain
in
the
cycle is a type of replication in which a virus
lysogenic
does not immediately kill a host cell.
The
however, some type of environmental stimulus
lysogenic cycle in a bacteria cell is shown on
eventually results in the separation of a
the right side of the figure on the next page.
prophage from the chromosome of its host
STOP. The figure shows both kinds of cycles.
cell. The viral DNA then enters the lytic
The lytic cycle has five steps and the lysogenic
cycle.
has three. (Summarizing or paraphrasing).
humans can go through the lysogenic cycle,
During the lysogenic cycle, viral DNA
cycle
indefinitely.
Usually,
The virus that causes cold sores in
for example.
Cold sores erupt when these
inserts itself into a host cell's chromosome. A
viruses enter the lytic cycle. STOP. I heard
viral DNA segment that is inserted in a
this on television that cold sores were caused
bacterial chromosome is called a prophage.
by a virus. (Reporting prior knowledge)
Division of Learning Services
Fall 2007
COMPREHENSION:
Characteristics of Viruses--Part II - Level High School - Science
1.
What is the passage mostly about?
Implicit: the two cycles of viral replication.
2.
How does a virus increase in number?
Explicit: it replicates.
3.
What does a virus need to replicate?
Explicit: a host.
4.
How is replication different from reproduction?
Explicit: reproduction requires cell division, and replication does not.
5.
What is the major difference between the lytic cycle and the lysogenic cycle?
Implicit: in the lytic cycle, the virus immediately begins to replicate and kill the host cell,
whereas in the lysogenic cycle, it doesn't kill the host cell.
6.
If a virus enters your body but you show no symptoms of a disease, what cycle is the virus in?
Implicit: the lysogenic cycle.
7.
In the lytic cycle, what role does DNA play in replication?
Implicit: it tells the cell to replicate or make new viruses or it carries the information
necessary for replication.
8.
If a cell's viral DNA separates from the cell's chromosome, what can we conclude?
Implicit: a stimulus has prompted it or the lytic cycle will begin soon.
9.
When a cold sore erupts, what cycle is the virus in?
Explicit: the lytic cycle.
10.
What happens to a prophage when the host cell divides?
Explicit: the prophage is replicated each time.
Number Correct Explicit: ______
Total Reading
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Number Correct Implicit: ______
Total
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Independent: 9-10 correct
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Instructional: 7-8 correct
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Frustration: 6 or less correct
Fall 2007
Student Name _________________________
Date ______________________________
Characteristics of Viruses--Part III
Level High School - Science
Prompt: This passage is called Characteristics
of Viruses. It is about viruses.
Now I want you to read the next
section, and when you come to the word
STOP in the text, I want you to tell me what
Viruses that infect only bacterial cells are
referred to as bacteriophages.
Many but not all viruses invade only a
When you have finished
specific type of organism. For example, the
reading, I will ask you to tell me what you
virus that causes polio replicates only inside
remember, and then I will ask you questions.
human host cells. The virus that causes rabies
you are thinking.
infects only the cells of a particular animal
Diversity of Viruses:
An Unending Supply
Classifying viruses is difficult because
they are so diverse. As a result, biologists
have developed several different ways of
organizing viruses. Sometimes they are
organized by shape, sometimes by the host
they infect. Viruses may also be classified
according to the way they function inside a
cell. STOP.
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Shape. The arrangement of proteins
in capsids determines the shape of the viruses.
species, such as dogs and humans. STOP.
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You may wonder how viruses can be
so specific. Earlier you learned that capsids
and envelopes contain specific proteins.
Receptor sites on host cells also contain
specific proteins. If the outer proteins in a
virus do not fit with the outer proteins of a
cell, the virus will not attach to the cell.
Without attachment, the viral nucleic acid
cannot enter the host cell to replicate. STOP.
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Host. Viruses can be organized
according to the type of host they infect.
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There are animal viruses, plant viruses, and
bacterial viruses.
Division of Learning Services
Fall 2007
(page 2: Characteristics of Viruses--Part III)
Retroviruses include tumor-producing
viruses as well as HIV. Tumor-producing
Function. Some viruses, such as
retroviruses and HIV follow a similar invasion
retroviruses, can also be classified based on
pattern. Many tumor-producing viruses,
how they function in a host. A retrovirus is a
however, enter the lysogenic cycle after Step 3
virus that contains an RNA code that replicates
in the figure. Tumors do not immediately
by first transcribing its RNA into DNA.
appear, but the viral DNA replicates along
The prefix "retro" means "reverse." What do
with the host cell DNA. Eventually many host
you think might work in reverse in this group
cells will contain tumor-producing viral DNA.
of viruses? STOP.
Using what you have learned about the
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lysogenic cycle, you can probably predict what
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will happen eventually. STOP.
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Most viruses and all organisms make
RNA from DNA in the process of
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transcription. Retroviruses are able to make
nucleic acids in reverse order from the usual
Nonviral particles. Scientists have
process. In retroviruses DNA is made from
discovered two infectious agents that have
RNA. As you can see in the figure on the next
simpler structures than viruses: viroids and
page, retroviruses have an enzyme called
prions. A viroid is a single strand of pure
reverse transcriptase, which transcribes viral
RNA. Viroids cause plant disease. For
RNA into viral DNA inside the host cell. You
example, viroids have killed many coconut
can study the figure to better understand the
palm trees in the Philippines. Other viroids
replication of a human immunodeficiency
affect the health of crops such as potatoes and
virus (HIV) The retrovirus causes acquired
tomatoes. Unlike viruses, viroids do not have
immunodeficiency syndrome (AIDS). STOP.
capsids protecting their nucleic acids. STOP.
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Division of Learning Services
Fall 2007
(page 3: Characteristics of Viruses--Part III)
A prion is a protein molecule that can
cause disease in animals. Prions are the only
known infectious agents that do not contain
DNA or RNA but can, nonetheless, spread
throughout an organism. A prion causes a
fatal disease called scrapie in sheep. Prions
have also been found in the brains of cows that
died from the so-called mad cow disease.
Other prions are found in humans who suffer
from kuru or Creutzfeldt-Jakob disease. Both
of these diseases affect the central nervous
system. A cure has not yet been found for
diseases caused by viroids or prions. STOP.
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Think-Aloud Summary
Think-Aloud Statements That Indicate
Understanding
Paraphrasing/Summarizing
_____
Making New Meaning
_____
Questioning That Indicates Understanding
_____
Noting Understanding
_____
Reporting Prior Knowledge
_____
Identifying Personally
_____
Think-Aloud Statements That Indicate Lack of
Understanding
Division of Learning Services
Fall 2007
COMPREHENSION:
Characteristics of Viruses--Part III - Level High School - Science
1.
What are the major topics included in this section?
Implicit: any two of the following: how viruses are classified, retroviruses, and nonviral
particles.
2.
Name three ways in which viruses are classified.
Explicit: by shape, host, and the way they function.
3.
What is necessary for the virus to attach to a host?
Explicit: the outer proteins must match.
4.
What is a retrovirus?
Explicit: a virus that replicates by first transcribing its RNA into DNA.
5.
How do retroviruses and other viruses differ?
Implicit: regular viruses make RNA from DNA.
6.
What enzyme is necessary for HIV to replicate?
Explicit in figure: reverse transcriptase.
7.
What are the two types of illnesses caused by a retrovirus?
Explicit: AIDS and tumors (Cancer is acceptable.)
8.
What happens when tumor-producing viral DNA goes into the lytic cycle?
Implicit: tumors are produced.
9.
If a person is found to be HIV positive but shows no symptoms of AIDS, what cycle is the
HIV virus in?
Implicit: the lysogenic cycle.
10.
How are viroids and prions alike, and how are they different?
Implicit: they are both infectious agents, and no cure has been found for the diseases they
produce but viroids cause plant diseases and prions cause animal diseases. (Answer should
include one likeness and one difference.)
Number Correct Explicit: ______
Total Reading
Word Accuracy
Independent
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Comprehension
Independent
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Independent
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Independent
Instructional
Division of Learning Services
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Independent
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Number Correct Implicit: ______
Total
______
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Independent: 9-10 correct
____________
Instructional: 7-8 correct
____________
Frustration: 6 or less correct
Fall 2007