Student Name Characteristics of Viruses--Part I Level High School - Science Date _ 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 environment. 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.
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.) Total Reading Word Accuracy Comprehension Reading Level Independent + Independent = Independent Independent + Instructional = Instructional Independent + Frustration = Frustration Instructional + Independent = Instructional Instructional + Instructional = Instructional Instructional + Frustration = Frustration Frustration + Independent = Frustration Frustration + Instructional = Frustration Number Correct Explicit: _ Number Correct Implicit: _ Total Independent: 9-10 correct Instructional: 7-8 correct Frustration: 6 or less correct
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 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. Viral Replication: Ticking Time Bobs Viruses do not reproduce, they replicate. STOP. I'm wondering what is the difference? (Questioning) Reproduction, which is characteristic of living things, involves cell division. Replication does not involve cell division. STOP. Well, they answered my question. (Noting understanding). Viruses cannot replicate on their own. In order to replicate, viruses require a host. STOP. I remember learning about a host in science. (Reporting prior knowledge) A host is an organism that shelters and nourishes something. Living cells host viruses. These host cells provide all the materials that viruses need to copy themselves. STOP. So the viruses feed off the host sort of like a parasite. (Making new meaning) When it enters a host cell, a virus may immediately begin to replicate, or it may remain relatively inactive. STOP. We 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. (Noting understanding) The lytic cycle begins when a 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. (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 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.
(page 2: Characteristics of Viruses--Part II) STOP. I remember when I had the chicken pox. I was miserable (Identifying personally). Sometimes a virus does not start the lytic cycle immediately. Instead the virus enters the lysogenic cycle. The lysogenic cycle is a type of replication in which a virus does not immediately kill a host cell. The lysogenic cycle in a bacteria cell is shown on the right side of the figure on the next page. STOP. The figure shows both kinds of cycles. The lytic cycle has five steps and the lysogenic has three. (Summarizing or paraphrasing). During the lysogenic cycle, viral DNA inserts itself into a host cell's chromosome. A viral DNA segment that is inserted in a bacterial chromosome is called a prophage. A host cell carrying a prophage may divide many times. The prophage is replicated every time the host cell's chromosome replicates. STOP. I get the idea of the prophage (Noting understanding) Some prophages remain in the lysogenic cycle indefinitely. Usually, however, some type of environmental stimulus eventually results in the separation of a prophage from the chromosome of its host cell. The viral DNA then enters the lytic cycle. The virus that causes cold sores in humans can go through the lysogenic cycle, for example. Cold sores erupt when these viruses enter the lytic cycle. STOP. I heard this on television that cold sores were caused by a virus. (Reporting prior knowledge)
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. Total Reading Word Accuracy Comprehension Reading Level Independent + Independent = Independent Independent + Instructional = Instructional Independent + Frustration = Frustration Instructional + Independent = Instructional Instructional + Instructional = Instructional Instructional + Frustration = Frustration Frustration + Independent = Frustration Frustration + Instructional = Frustration Number Correct Explicit: _ Number Correct Implicit: _ Total Independent: 9-10 correct Instructional: 7-8 correct Frustration: 6 or less correct
Student Name Characteristics of Viruses--Part III Level High School - Science Date 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 you are thinking. When you have finished reading, I will ask you to tell me what you remember, and then I will ask you questions. 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. Shape. The arrangement of proteins in capsids determines the shape of the viruses. Host. Viruses can be organized according to the type of host they infect. There are animal viruses, plant viruses, and bacterial viruses. Viruses that infect only bacterial cells are referred to as bacteriophages. Many but not all viruses invade only a specific type of organism. For example, the virus that causes polio replicates only inside human host cells. The virus that causes rabies infects only the cells of a particular animal species, such as dogs and humans. STOP. 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.
(page 2: Characteristics of Viruses--Part III) Function. Some viruses, such as retroviruses, can also be classified based on how they function in a host. A retrovirus is a virus that contains an RNA code that replicates by first transcribing its RNA into DNA. The prefix "retro" means "reverse." What do you think might work in reverse in this group of viruses? STOP. Most viruses and all organisms make RNA from DNA in the process of transcription. Retroviruses are able to make nucleic acids in reverse order from the usual process. In retroviruses DNA is made from RNA. As you can see in the figure on the next page, retroviruses have an enzyme called reverse transcriptase, which transcribes viral RNA into viral DNA inside the host cell. You can study the figure to better understand the replication of a human immunodeficiency virus (HIV) The retrovirus causes acquired immunodeficiency syndrome (AIDS). STOP. Retroviruses include tumor-producing viruses as well as HIV. Tumor-producing retroviruses and HIV follow a similar invasion pattern. Many tumor-producing viruses, however, enter the lysogenic cycle after Step 3 in the figure. Tumors do not immediately appear, but the viral DNA replicates along with the host cell DNA. Eventually many host cells will contain tumor-producing viral DNA. Using what you have learned about the lysogenic cycle, you can probably predict what will happen eventually. STOP. Nonviral particles. Scientists have discovered two infectious agents that have simpler structures than viruses: viroids and prions. A viroid is a single strand of pure RNA. Viroids cause plant disease. For example, viroids have killed many coconut palm trees in the Philippines. Other viroids affect the health of crops such as potatoes and tomatoes. Unlike viruses, viroids do not have capsids protecting their nucleic acids. STOP.
(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. 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
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 Comprehension Reading Level Independent + Independent = Independent Independent + Instructional = Instructional Independent + Frustration = Frustration Instructional + Independent = Instructional Instructional + Instructional = Instructional Instructional + Frustration = Frustration Frustration + Independent = Frustration Frustration + Instructional = Frustration Number Correct Implicit: _ Total Independent: 9-10 correct Instructional: 7-8 correct Frustration: 6 or less correct