A virus consists of a nucleic acid surrounded by a protein coat. [2]

Transcription

1 GUIDED READING - Ch VIRUSES NAME: Please print out these pages and HANDWRITE the answers directly on the printouts. Typed work or answers on separate sheets of paper will not be accepted. Importantly, guided readings are NOT GROUP PROJECTS!!! You, and you alone, are to answer the questions as you read. You are not to share them with another students or work together on filling it out. Please report any dishonest behavior to your instructor to be dealt with accordingly. Get in the habit of writing legibly, neatly, and in a NORMAL, MEDIUM-SIZED FONT. AP essay readers and I will skip grading anything that cannot be easily and quickly read so start perfect your handwriting. Please SCAN documents properly and upload them to Archie. Avoid taking photographs of or uploading dark, washed out, side ways, or upside down homework. Please use the scanner in the school s media lab if one is not at your disposal and keep completed guides organized in your binder to use as study and review tools. READ FOR UNDERSTANDING and not merely to complete an assignment. Though all the answers are in your textbook, you should try to put answers in your own words, maintaining accuracy and the proper use of terminology, rather than blindly copying the textbook whenever possible. Experimental work with viruses has provided important evidence that genes are made of nucleic acids. Viruses were also important in working out the molecular mechanisms of DNA replication, transcription, and translation. Viruses have even been important in the development of techniques of manipulating and transferring genes. [2] A virus consists of a nucleic acid surrounded by a protein coat. [2] What did Dr. Mayer discover in 1883? [3] a. What procedure did Dimitri Ivanowsky perform to isolate the causal agent of Tobacco Mosaic Disease? b. What were his conclusions?

2 3. What was the logic behind Beijerinck s investigation that led to his concept of the virus? Be specific about how he rationalized that it must be a reproducing pathogen and not toxins derived from the pathogen that caused Tobacco Mosaic Disease. 4. How was the existence of a virus finally confirmed and by whom? [2] 5. How small are viruses? [3] 6. Describe is the make-up and organization of the four forms of viral genomes? [2] 7. What two macromolecules are most viruses composed of? 8. a. What is a capsid? [2] b. What are capsomers? [2] c. Describe some of the different shapes capsids may have? [2]

3 9. a. As you see, all viruses consist of a nucleic acid (DNA or RNA) enclosed in a protein coat. Some viruses also have a membranous envelope. [2] What are animal virus viral envelopes and what are their functions/roles? [3] b. What are the components of a viral envelope? Which component is derived from the host cell and which is of viral origin? [2] 10. Describe the structure of the Influenza virus, a virus with an envelope. Include a drawing as part of your explanation. 1 Of all viruses, which have the most complex capsids? 1 For the phage virus shown below, label the protein capsid, tail fibers, head, tail sheath, and genome. Viruses reproduce only in host cells. [2] 13. Why are viruses referred to as obligate intracellular parasites? 14. a. What is meant by a virus s host range?

4 b. What property of a virus determines its attachment to a host cell membrane? [2] c. What is the difference between a virus with a broad host range and one with an extremely limited host range. Give an example of each as well. [2] 15. Compare the host range for the rabies virus to that of the human cold virus. Be species as to the species and/or the cell types within the species that can be infected. [2] 16. What components of the host cell does a virus use to reproduce itself? 17. How does a DNA virus reproduce its genome? [2] 18. How do most RNA viruses replicate their genome? [2]

5 19. Name & describe the generic steps of viral reproductive cycles a. What are bacteriophages? [2] b. What portion of a phage enters the host cell? [2] 2 a. What is a phage called that reproduces by a lytic cycle only? [2] b. What is a phage called that reproduces by a lytic or lysogenic cycle? 2 a. Elaborate on the defense mechanisms used by bacteria to defend themselves against phages.

6 b. How does the bacteria producing these restriction enzymes ensure that its own genome does no get destroyed in this process of defending against viral infections. 23. What are three ways bacteria may win the battle against the phages? [2] Elaborate on the five steps of the phage lytic cycle? What is prophage? 26. Since cells that have incorporated phage DNA into their genome may continue to divide and propagate the viral genome, this might be considered somewhat like the Trojan horse. What might trigger the switchover from lysogenic to lytic mode. [2]

7 27. Detail the reproductive cycle of a lysogenic phage by labeling the illustration below. 28. There are some general differences between bacteriophages and animal viruses. What are two elements that many animal viruses have? [2] 29. In contrast to most bacteriophages, many animal viruses have an outer membrane called a viral envelope. a. What do these viruses use an envelope for? b. In a bit more detail this time, from where and how do viral envelopes originate? c. What is the role of the envelope glycoproteins and from where do these originate?

8 30. Enveloped viruses enter the host cell through fusion with the host s plasma membrane or through endocytosis. Does the reproductive cycle of enveloped viruses kill the host cell like that of lytic bacteriophages does? Explain. 3 Some viruses remain in the cytoplasm while others invade the nucleus as part of their reproductive cycle. Why is it the case that a person is infected with herpes virus continues to have flare-ups of cold sores or genital sores throughout their lives? 3 Under the Baltimore Classification System of viruses, all viruses are classified into one of seven classes (I-VII). (Class I and II viruses contain double-stranded and single-stranded DNA, respectively. Class III viruses are the double-stranded RNA viruses. Class IV and V viruses contain single-stranded positive or negative sense RNA. Class VI viruses contain positive sense singlestranded RNA viruses that replicate through a DNA intermediate. Finally, Class VII viruses contain double-stranded DNA, but replicate through a single-stranded RNA intermediate.) What is the difference between class IV, class V, and class VI singlestranded RNA viruses as mentioned in your text. (Be sure to define reverse transcriptase as part of your explanation). 33. Explain the process depicted below through which an RNA virus is able to reproduce without possessing or ever even synthesizing DNA. [1]

9 34. a. What is a retrovirus? b. How do retroviruses, such as HIV replicate their genome? [2] 35. a. What does HIV stand for? b. What is the syndrome called caused by HIV once the virus has destroyed key cells in the human s immune system? c. Here is a sketch of HIV. Label these parts: envelope, reverse transcriptase, RNA, and capsid. [2] 36. a. Describe the difference between a prophage and a provirus? b. Which one are you likely to carry? [2]

10 37. Label the illustration below detailing the reproductive cycle of HIV, the retrovirus that causes AIDS.

11 38. a. Is it believed that viruses evolved before or after the first cells appeared? b. Describe the two possible sources of viral genomes. You will see each of these important mobile genetic elements again. [2] Viruses, viroids, and prions are formidable pathogens in animals and plants. [2] 39. a. What are three ways that viruses make us ill? [2] 3. b. Why do we recover completely from a cold but not from polio? [2] 40. What are vaccines? 4 Emerging viruses such as HIV, Ebola, and SARS seem to burst upon the human scene. [2] What three processes contribute to the emergence of viral diseases?

12 3. 4 What is the difference between an epidemic and a pandemic? 43. List and describe the two main routes of viral transmission in plants? 44. How do viruses spread throughout plant bodies? 45. a. What are viroids? [2] b. What important lesson do they teach? [2]

13 c. Name one viroid disease. [2] 46. a. What are prions? b. What characteristics of prions make them especially dangerous? c. How are prions transmitted? [2] d. How do prions cause pathology? e. Name four diseases caused by prions. [2] 47. Please answer the Self-Quiz at the end of your chapter. Do your best to try it from memory first in order to test how well you grasped the material References Campbell et al. (2008). AP* Edition Biology. 8th Ed. San Francisco: Pearson Benjamin Cummings. Adapted from Fred and Theresa Holtzclaw 3. Adapted from L. Miriello